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Networking Guide

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Red Hat Enterprise Linux 7

Configuring and managing networks, network interfaces, and network services in RHEL 7

Marc Muehlfeld

Red Hat Customer Content Services

Ioanna Gkioka

Red Hat Customer Content Services

Mirek Jahoda

Red Hat Customer Content Services

Jana Heves

Red Hat Customer Content Services

Stephen Wadeley

Red Hat Customer Content Services

Christian Huffman

Red Hat Customer Content Services

Abstract

The Red Hat Enterprise Linux 7 Networking Guide documents relevant information regarding the configuration and administration of network interfaces, networks and network services in Red Hat Enterprise Linux. It is oriented towards system administrators with a basic understanding of Linux and networking.

Note

To expand your expertise, you might also be interested in the Red Hat System Administration I (RH124) training course.

Part I. Before You Begin

This documentation part provides an overview of basic concepts of the network services in Red Hat Enterprise Linux.

Chapter 1. Overview of Networking Topics

1.1. Comparing IP to non-IP Networks

Network is a system of interconnected devices that can communicate sharing information and resources, such as files, printers, applications, and Internet connection. Each of these devices has a unique Internet Protocol (IP) address to send and receive messages between two or more devices using a set of rules called protocol.

Categories of Network Communication

IP Networks
Networks that communicate through Internet Protocol addresses. An IP network is implemented in the Internet and most internal networks. Ethernet, Cable Modems, DSL Modems, dial up modems, wireless networks, and VPN connections are typical examples.
non-IP Networks
Networks that are used to communicate through a lower layer rather than the transport layer. Note that these networks are rarely used. InfiniBand is a non-IP network, described in Chapter 13, Configure InfiniBand and RDMA Networks.

1.2. Comparing Static to Dynamic IP Addressing

Static IP addressing
When a device is assigned a static IP address, the address does not change over time unless changed manually. It is recommended to use static IP addressing if you want:
  • To ensure network address consistency for servers such as DNS, and authentication servers.
  • To use out-of-band management devices that work independently of other network infrastructure.
All the configuration tools listed in Section 3.1, “Selecting Network Configuration Methods” allow assigning static IP addresses manually. The nmcli tool is also suitable, described in Section 3.3.8, “Adding and Configuring a Static Ethernet Connection with nmcli” .
For more information on automated configuration and management, see the OpenLMI chapter in the Red Hat Enterprise Linux 7 System Administrators Guide. The Red Hat Enterprise Linux 7 Installation Guide documents the use of a Kickstart file which can also be used for automating the assignment of network settings.
Dynamic IP addressing
When a device is assigned a dynamic IP address, the address changes over time. For this reason, it is recommended for devices that connect to the network occasionally because IP address might be changed after rebooting the machine.
Dynamic IP addresses are more flexible, easier to set up and administer. The dynamic host control protocol (DHCP) is a traditional method of dynamically assigning network configurations to hosts. See Section 14.1, “Why Use DHCP?” for more information. You can also use the nmcli tool, described in Section 3.3.7, “Adding and Configuring a Dynamic Ethernet Connection with nmcli” .

Note

There is no strict rule defining when to use static or dynamic IP address. It depends on user's needs, preferences and the network environment.
By default, NetworkManager calls the DHCP client, dhclient.

1.3. Configuring the DHCP Client Behavior

A Dynamic Host Configuration Protocol (DHCP) client requests the dynamic IP address and corresponding configuration information from a DHCP server each time a client connects to the network.
Note that NetworkManager calls the DHCP client, dhclient by default.

Requesting an IP Address

When a DHCP connection is started, a dhcp client requests an IP address from a DHCP server. The time that a dhcp client waits for this request to be completed is 60 seconds by default. You can configure the ipv4.dhcp-timeout property using the nmcli tool or the IPV4_DHCP_TIMEOUT option in the /etc/sysconfig/network-scripts/ifcfg-ifname file. For example, using nmcli: 
~]# nmcli connection modify enp1s0 ipv4.dhcp-timeout 10
If an address cannot be obtained during this interval, the IPv4 configuration fails. The whole connection may fail, too, and this depends on the ipv4.may-fail property:
  • If ipv4.may-fail is set to yes (default), the state of the connection depends on IPv6 configuration:
    1. If the IPv6 configuration is enabled and successful, the connection is activated, but the IPv4 configuration can never be retried again.
    2. If the IPv6 configuration is disabled or does not get configured, the connection fails.
  • If ipv4.may-fail is set to no the connection is deactivated. In this case:
    1. If the autoconnect property of the connection is enabled, NetworkManager retries to activate the connection as many times as set in the autoconnect-retries property. The default is 4.
    2. If the connection still cannot acquire the dhcp address, auto-activation fails.
      Note that after 5 minutes, the auto-connection process starts again and the dhcp client retries to acquire an address from the dhcp server.

Requesting a Lease Renewal

When a dhcp address is acquired and the IP address lease cannot be renewed, the dhcp client is restarted for three times every 2 minutes to try to get a lease from the dhcp server. Each time, it is configured by setting the ipv4.dhcp-timeout property in seconds (default is 60) to get the lease. If you get a reply during your attempts, the process stops and you get your lease renewed.
After three attempts failed:
  • If ipv4.may-fail is set to yes (default) and IPv6 is successfully configured, the connection is activated and the dhcp client is restarted again every 2 minutes.
  • If ipv4.may-fail is set to no, the connection is deactivated. In this case, if the connection has the autoconnect property enabled, the connection is activated from scratch.

1.3.1. Making DHCPv4 Persistent

To make DHCPv4 persistent both at startup and during the lease renewal processes, set the ipv4.dhcp-timeout property either to the maximum for a 32-bit integer (MAXINT32), which is 2147483647, or to the infinity value: 
~]$ nmcli connection modify enps1s0 ipv4.dhcp-timeout infinity
As a result, NetworkManager never stops trying to get or renew a lease from a DHCP server until it is successful.
To ensure a DHCP persistent behavior only during the lease renewal process, you can manually add a static IP to the IPADDR property in the /etc/sysconfig/network-scripts/ifcfg-enp1s0 configuration file or by using nmcli: 
~]$ nmcli connection modify enp1s0 ipv4.address 192.168.122.88/24
When an IP address lease expires, the static IP preserves the IP state as configured or partially configured (you can have an IP address, but you are not connected to the Internet), making sure that the dhcp client is restarted every 2 minutes.

1.4. Setting the Wireless Regulatory Domain

In Red Hat Enterprise Linux, the crda package contains the Central Regulatory Domain Agent that provides the kernel with the wireless regulatory rules for a given jurisdiction. It is used by certain udev scripts and should not be run manually unless debugging udev scripts. The kernel runs crda by sending a udev event upon a new regulatory domain change. Regulatory domain changes are triggered by the Linux wireless subsystem (IEEE-802.11). This subsystem uses the regulatory.bin file to keep its regulatory database information.
The setregdomain utility sets the regulatory domain for your system. Setregdomain takes no arguments and is usually called through system script such as udev rather than manually by the administrator. If a country code look-up fails, the system administrator can define the COUNTRY environment variable in the /etc/sysconfig/regdomain file.
See the following man pages for more information about the regulatory domain:
  • setregdomain(1) man page — Sets regulatory domain based on country code.
  • crda(8) man page — Sends to the kernel a wireless regulatory domain for a given ISO or IEC 3166 alpha2.
  • regulatory.bin(5) man page — Shows the Linux wireless regulatory database.
  • iw(8) man page — Shows or manipulates wireless devices and their configuration.

1.5. Configuring netconsole

If disk logging fails or using the serial console is not possible, you might need to use kernel debugging. The netconsole kernel module enables to log kernel messages to another computer over the network.
To be able to use netconsole, you need to have an rsyslog server that is properly configured on your network.

Procedure 1.1. Configuring an rsyslog server for netconsole

  1. Configure the rsyslogd daemon to listen on the 514/udp port and receive messages from the network by uncommenting the following lines in the MODULES section of the /etc/rsyslog.conf file: 
    $ModLoad imudp
$UDPServerRun 514
  2. Restart the rsyslogd service for the changes to take effect: 
    ]# systemctl restart rsyslog
  3. Verify that rsyslogd is listening on the 514/udp port: 
    ]# netstat -l | grep syslog
udp        0      0 0.0.0.0:syslog          0.0.0.0:*
udp6       0      0 [::]:syslog             [::]:*
    The 0.0.0.0:syslog and [::]:syslog values in the netstat -l output mean that rsyslogd is listening on default netconsole port defined in the /etc/services file: 
    ]$ cat /etc/services | grep syslog
syslog          514/udp
syslog-conn     601/tcp                 # Reliable Syslog Service
syslog-conn     601/udp                 # Reliable Syslog Service
syslog-tls      6514/tcp                # Syslog over TLS
syslog-tls      6514/udp                # Syslog over TLS
syslog-tls      6514/dccp               # Syslog over TLS
Netconsole is configured using the /etc/sysconfig/netconsole file, which is a part of the initscripts package. This package is installed by default and it also provides the netconsole service.
If you want to configure a sending machine, follow this procedure:

Procedure 1.2. Configuring a Sending Machine

  1. Set the value of the SYSLOGADDR variable in the /etc/sysconfig/netconsole file to match the IP address of the syslogd server. For example: 
    SYSLOGADDR=192.168.0.1
  2. Restart the netconsole service for the changes to take effect: 
    ]# systemctl restart netconsole.service
  3. Enable netconsole.service to run after rebooting the system: 
    ]# systemctl enable netconsole.service
  4. View the netconsole messages from the client in the /var/log/messages file (default) or in the file specified in rsyslog.conf. 
    ]# cat /var/log/messages

Note

By default, rsyslogd and netconsole.service use port 514. To use a different port, change the following line in /etc/rsyslog.conf to the required port number: 
$UDPServerRun <PORT>
On the sending machine, uncomment and edit the following line in the /etc/sysconfig/netconsole file: 
SYSLOGPORT=514
For more information about netconsole configuration and troubleshooting tips, see Netconsole Kernel Documentation.

1.6. Using Network Kernel Tunables with sysctl

Using certain kernel tunables through the sysctl utility, you can adjust network configuration on a running system and directly affect the networking performance.
To change network settings, use the sysctl commands. For permanent changes that persist across system restarts, add lines to the /etc/sysctl.conf file.
To display a list of all available sysctl parameters, enter as root: 
~]# sysctl -a
For more details on network kernel tunables using sysctl, see the Using PTP with Multiple Interfaces section in the System Administrator's Guide.
For more information on network kernel tunables, see the Network Interface Tunables section in the Kernel Administration Guide.

1.7. Managing Data Using the ncat utility

The ncat networking utility replaces netcat in Red Hat Enterprise Linux 7. ncat is a reliable back-end tool that provides network connectivity to other applications and users. It reads and writes data across the network from the command line, and uses Transmission Control Protocol (TCP), User Datagram Protocol (UDP), Stream Control Transmission Protocol (SCTP) or Unix sockets for communication. ncat can deal with both IPv4 and IPv6, open connections, send packets, perform port scanning, and supports higher-level features such as SSL, and connection broker.
The nc command can also be entered as ncat, using the identical options. For more information about the ncat options, see the New networking utility (ncat) section in the Migration Planning Guide and the ncat(1) man page.

Installing ncat

To install the ncat package, enter as root: 
~]# yum install ncat

Brief Selection of ncat Use Cases

Example 1.1. Enabling Communication between a Client and a Server

  1. Set a client machine to listen for connections on TCP port 8080: 
    ~]$ ncat -l 8080
  2. On a server machine, specify the IP address of the client and use the same port number: 
    ~]$ ncat 10.0.11.60 8080
    You can send messages on either side of the connection and they appear on both local and remote machines.
  3. Press Ctrl+D to close the TCP connection.

Note

To check a UDP port, use the same nc commands with the –u option. For example: 
~]$ ncat -u -l 8080

Example 1.2. Sending Files

Instead of printing information on the screen, as mentioned in the previous example, you can send all information to a file. For example, to send a file over TCP port 8080 from a client to a server:
  1. On a client machine, to listen a specific port transferring a file to the server machine: 
    ~]$  ncat -l 8080 > outputfile
  2. On a server machine, specify the IP address of the client, the port and the file which is to be transferred: 
    ~]$  ncat -l 10.0.11.60 8080 < inputfile
After the file is transferred, the connection closes automatically.

Note

You can transfer a file in the other direction as well: 
~]$  ncat -l 8080 < inputfile
~]$  ncat -l 10.0.11.60 8080 > outputfile

Example 1.3. Creating an HTTP proxy server

To create an HTTP proxy server on localhost port 8080: 
~]$  ncat -l --proxy-type http localhost 8080

Example 1.4. Port Scanning

To view which ports are open, use the –z option and specify a range of ports to scan: 
~]$  ncat -z 10.0.11.60 80-90
    Connection to 192.168.0.1 80 port [tcp/http] succeeded!

Example 1.5. Setting up Secure Client-Server Communication Using SSL

Set up SSL on a server: 
~]$ ncat -e /bin/bash -k -l 8080 --ssl
On a client machine: 
~]$ ncat --ssl 10.0.11.60 8080

Note

To ensure true confidentiality of the SSL connection, the server requires the --ssl-cert and --ssl-key options, and the client requires the --ssl-verify and --ssl-trustfile options. For information on OpenSSL, see the Using OpenSSL section in the Security Guide.
For more examples, see the ncat(1) man page.

Part II. Managing IP Networking

This documentation part provides detailed instruction on how to configure and manage networking in Red Hat Enterprise Linux.

Chapter 2. Getting Started with NetworkManager

2.1. Overview of NetworkManager

In Red Hat Enterprise Linux 7, the default networking service is provided by NetworkManager, which is a dynamic network control and configuration daemon to keep network devices and connections up and active when they are available. The traditional ifcfg type configuration files are still supported. See Section 2.6, “Using NetworkManager with Network Scripts” for more information.

2.1.1. Benefits of Using NetworkManager

The main benefits of using NetworkManager are:
  • Making Network management easier: NetworkManager ensures that network connectivity works. When it detects that there is no network configuration in a system but there are network devices, NetworkManager creates temporary connections to provide connectivity.
  • Providing easy setup of connection to the user: NetworkManager offers management through different tools — GUI, nmtui, nmcli —. See Section 2.5, “NetworkManager Tools”.
  • Supporting configuration flexibility. For example, configuring a WiFi interface, NetworkManager scans and shows the available wifi networks. You can select an interface, and NetworkManager displays the required credentials providing automatic connection after the reboot process. NetworkManager can configure network aliases, IP addresses, static routes, DNS information, and VPN connections, as well as many connection-specific parameters. You can modify the configuration options to reflect your needs.
  • Offering an API through D-Bus which allows applications to query and control network configuration and state. In this way, applications can check or configure networking through D-BUS. For example, the web console interface, which monitors and configures servers through a web browser, uses the NetworkManager D-BUS interface to configure networking.
  • Maintaining the state of devices after the reboot process and taking over interfaces which are set into managed mode during restart.
  • Handling devices which are not explicitly set unmanaged but controlled manually by the user or another network service.

2.2. Installing NetworkManager

NetworkManager is installed by default on Red Hat Enterprise Linux. If it is not, enter as root: 
~]# yum install NetworkManager
For information on user privileges and gaining privileges, see the Red Hat Enterprise Linux System Administrator's Guide.

2.3. Checking the Status of NetworkManager

To check whether NetworkManager is running: 
~]$ systemctl status NetworkManager
NetworkManager.service - Network Manager
   Loaded: loaded (/lib/systemd/system/NetworkManager.service; enabled)
   Active: active (running) since Fri, 08 Mar 2013 12:50:04 +0100; 3 days ago
Note that the systemctl status command displays Active: inactive (dead) when NetworkManager is not running.

2.4. Starting NetworkManager

To start NetworkManager: 
~]# systemctl start NetworkManager
To enable NetworkManager automatically at boot time: 
~]# systemctl enable NetworkManager
For more information on starting, stopping and managing services, see the Red Hat Enterprise Linux System Administrator's Guide.

2.5. NetworkManager Tools

Table 2.1. A Summary of NetworkManager Tools and Applications
Application or ToolDescription
nmcliA command-line tool which enables users and scripts to interact with NetworkManager. Note that nmcli can be used on systems without a GUI such as servers to control all aspects of NetworkManager. It has the same functionality as GUI tools.
nmtuiA simple curses-based text user interface (TUI) for NetworkManager
nm-connection-editorA graphical user interface tool for certain tasks not yet handled by the control-center utility such as configuring bonds and teaming connections. You can add, remove, and modify network connections stored by NetworkManager. To start it, enter nm-connection-editor in a terminal: 
~]$ nm-connection-editor
control-centerA graphical user interface tool provided by the GNOME Shell, available for desktop users. It incorporates a Network settings tool. To start it, press the Super key to enter the Activities Overview, type Network and then press Enter. The Network settings tool appears.
network connection iconA graphical user interface tool provided by the GNOME Shell representing network connection states as reported by NetworkManager. The icon has multiple states that serve as visual indicators for the type of connection you are currently using.

2.6. Using NetworkManager with Network Scripts

This section describes how to run a script and how to use custom commands in network scripts.
The term network scripts refers to the script /etc/init.d/network and any other installed scripts it calls. Although NetworkManager provides the default networking service, scripts and NetworkManager can run in parallel and work together. Red Hat recommends to test them first.

Running Network Script

Run a network script only with the systemctl command: 
systemctl start|stop|restart|status network
The systemctl utility clears any existing environment variables and ensures correct execution.
In Red Hat Enterprise Linux 7, NetworkManager is started first, and /etc/init.d/network checks with NetworkManager to avoid tampering with NetworkManager's connections. NetworkManager is intended to be the primary application using sysconfig configuration files, and /etc/init.d/network is intended to be secondary.
The /etc/init.d/network script runs:
  1. manually - using one of the systemctl commands start|stop|restart network,
    or
  2. on boot and shutdown if the network service is enabled - as a result of the systemctl enable network command.
It is a manual process and does not react to events that happen after boot. Users can also call the ifup and ifdown scripts manually.

Note

The systemctl reload network.service command does not work due to technical limitations of initscripts. To apply a new configuration for the network service, use the restart command: 
~]# systemctl restart network.service
This brings down and brings up all the Network Interface Cards (NICs) to load the new configuration. For more information, see the Red Hat Knowledgebase solution Reload and force-reload options for network service.

Using Custom Commands in Network Scripts

Custom commands in the /sbin/ifup-local, ifdown-pre-local, and ifdown-local scripts are only executed if these devices are controlled by the /etc/init.d/network service. The ifup-local file does not exist by default. If required, create it under the /sbin/ directory.
The ifup-local script is readable only by the initscripts and not by NetworkManager. To run a custom script using NetworkManager, create it under the dispatcher.d/ directory. See the section called “Running Dispatcher scripts”.

Important

Modifying any files included with the initscripts package or related rpms is not recommended. If a user modifies such files, Red Hat does not provide support.
Custom tasks can run when network connections go up and down, both with the old network scripts and with NetworkManager. If NetworkManager is enabled, the ifup and ifdown script will ask NetworkManager whether NetworkManager manages the interface in question, which is found from the “DEVICE=” line in the ifcfg file.
Devices managed by NetworkManager:
calling ifup
When you call ifup and the device is managed by NetworkManager, there are two options:
  • If the device is not already connected, then ifup asks NetworkManager to start the connection.
  • If the device is already connected, then nothing to do.
calling ifdown
When you call ifdown and the device is managed by NetworkManager:
  • ifdown asks NetworkManager to terminate the connection.
Devices unmanaged by NetworkManager:
If you call either ifup or ifdown, the script starts the connection using the older, non-NetworkManager mechanism that it has used since the time before NetworkManager existed.

Running Dispatcher scripts

NetworkManager provides a way to run additional custom scripts to start or stop services based on the connection status. By default, the /etc/NetworkManager/dispatcher.d/ directory exists and NetworkManager runs scripts there, in alphabetical order. Each script must be an executable file owned by root and must have write permission only for the file owner. For more information about running NetworkManager dispatcher scripts, see the Red Hat Knowledgebase solution How to write a NetworkManager dispatcher script to apply ethtool commands.

2.7. Using NetworkManager with sysconfig files

The /etc/sysconfig/ directory is a location for configuration files and scripts. Most network configuration information is stored there, with the exception of VPN, mobile broadband and PPPoE configuration, which are stored in the /etc/NetworkManager/ subdirectories. For example, interface-specific information is stored in the ifcfg files in the /etc/sysconfig/network-scripts/ directory.
For global settings, use the /etc/sysconfig/network file. Information for VPNs, mobile broadband and PPPoE connections is stored in /etc/NetworkManager/system-connections/.
In Red Hat Enterprise Linux 7 if you edit an ifcfg file, NetworkManager is not automatically aware of the change and has to be prompted to notice the change. If you use one of the tools to update NetworkManager profile settings, NetworkManager does not implement those changes until you reconnect using that profile. For example, if configuration files have been changed using an editor, NetworkManager must read the configuration files again.
To ensure this, enter as root to reload all connection profiles: 
~]# nmcli connection reload
Alternatively, to reload only one changed file, ifcfg-ifname: 
~]# nmcli con load /etc/sysconfig/network-scripts/ifcfg-ifname
Note that you can specify multiple file names using the above command.
Changes made using tools such as nmcli do not require a reload but do require the associated interface to be put down and then up again: 
~]# nmcli dev disconnect interface-name
~]# nmcli con up interface-name
For more details about nmcli, see Section 3.3, “Configuring IP Networking with nmcli”.
NetworkManager does not trigger any of the network scripts, though the network scripts attempt to trigger NetworkManager if it is running when the ifup commands are used. See Section 2.6, “Using NetworkManager with Network Scripts” for the explanation of the network scripts.
The ifup script is a generic script which does a few things and then calls interface-specific scripts such as ifup-device_name, ifup-wireless, ifup-ppp, and so on. When a user runs ifup enp1s0 manually:
  1. ifup looks for a file called /etc/sysconfig/network-scripts/ifcfg-enp1s0;
  2. if the ifcfg file exists, ifup looks for the TYPE key in that file to determine which type-specific script to call;
  3. ifup calls ifup-wireless or ifup-device_name based on TYPE;
  4. the type-specific scripts do type-specific setup;
  5. the type-specific scripts let common functions perform IP-related tasks like DHCP or static setup.
On bootup, /etc/init.d/network reads through all the ifcfg files and for each one that has ONBOOT=yes, it checks whether NetworkManager is already starting the DEVICE from that ifcfg file. If NetworkManager is starting that device or has already started it, nothing more is done for that file, and the next ONBOOT=yes file is checked. If NetworkManager is not yet starting that device, the initscripts continue with their traditional behavior and call ifup for that ifcfg file.
The result is that any ifcfg file that has ONBOOT=yes is expected to be started on system bootup, either by NetworkManager or by the initscripts. This ensures that some legacy network types which NetworkManager does not handle (such as ISDN or analog dial-up modems) as well as any new application not yet supported by NetworkManager are still correctly started by the initscripts even though NetworkManager is unable to handle them.

Important

It is recommended to not store the backup files anywhere within the /etc directory, or in the same location as the live files, because the script literally does ifcfg-*. Only these extensions are excluded: .old, .orig, .rpmnew, .rpmorig, and .rpmsave.
For more information on using sysconfig files, see Section 3.5, “Configuring IP Networking with ifcfg Files” and the ifcfg(8) man page.

2.8. Additional Resources

  • man(1) man page — Describes man pages and how to find them.
  • NetworkManager(8) man page — Describes the network management daemon.
  • NetworkManager.conf(5) man page — Describes the NetworkManager configuration file.
  • /usr/share/doc/initscripts-version/sysconfig.txt — Describes ifcfg configuration files and their directives as understood by the legacy network service.
  • /usr/share/doc/initscripts-version/examples/networking/ — A directory containing example configuration files.
  • ifcfg(8) man page — Describes briefly the ifcfg command.

Chapter 3. Configuring IP Networking

As a system administrator, you can configure a network interface either using NetworkManager or not.

3.1. Selecting Network Configuration Methods

3.2. Configuring IP Networking with nmtui

As a system administrator, you can configure a network interface using the NetworkManager's tool, nmtui. See Section 2.5, “NetworkManager Tools”.
This procedure describes how to configure networking using the text user interface tool, nmtui.
Prerequisites
  • The nmtui tool is used in a terminal window. It is contained in the NetworkManager-tui package, but it is not installed along with NetworkManager by default. To install NetworkManager-tui: 
    ~]# yum install NetworkManager-tui
  • To verify that NetworkManager is running, see Section 2.3, “Checking the Status of NetworkManager”.
Procedure
  1. Start the nmtui tool: 
    ~]$ nmtui
    The text user interface appears.
    The NetworkManager Text User Interface starting menu

    Figure 3.1. The NetworkManager Text User Interface starting menu

  2. To navigate, use the arrow keys or press Tab to step forwards and press Shift+Tab to step back through the options. Press Enter to select an option. The Space bar toggles the status of a check box.
To apply changes after a modified connection which is already active requires a reactivation of the connection. In this case, follow the procedure below:
Procedure
  1. Select the Activate a connection menu entry.
    Activate a Connection

    Figure 3.2. Activate a Connection

  2. Select the modified connection. On the right, click the Deactivate button.
    Deactivate the Modified Connection

    Figure 3.3. Deactivate the Modified Connection

  3. Choose the connection again and click the Activate button.
    Reactivate the Modified Connection

    Figure 3.4. Reactivate the Modified Connection

The following commands are also available: 
  • nmtui edit connection-name
    If no connection name is supplied, the selection menu appears. If the connection name is supplied and correctly identified, the relevant Edit connection screen appears. 
  • nmtui connect connection-name
    If no connection name is supplied, the selection menu appears. If the connection name is supplied and correctly identified, the relevant connection is activated. Any invalid command prints a usage message.
Note that nmtui does not support all types of connections. In particular, you cannot edit VPNs, wireless network connections using WPA Enterprise, or Ethernet connections using 802.1X.

3.3. Configuring IP Networking with nmcli

The nmcli (NetworkManager Command Line Interface) command-line utility is used for controlling NetworkManager and reporting network status. It can be utilized as a replacement for nm-applet or other graphical clients. See Section 2.5, “NetworkManager Tools”. nmcli is used to create, display, edit, delete, activate, and deactivate network connections, as well as control and display network device status.
The nmcli utility can be used by both users and scripts for controlling NetworkManager:
  • For servers, headless machines, and terminals, nmcli can be used to control NetworkManager directly, without GUI, including creating, editing, starting and stopping network connections and viewing network status.
  • For scripts, nmcli supports a terse output format which is better suited for script processing. It is a way to integrate network configuration instead of managing network connections manually.
The basic format of a nmcli command is as follows: 
nmcli [OPTIONS] OBJECT { COMMAND | help }
where OBJECT can be one of the following options: general, networking, radio, connection, device, agent, and monitor. You can use any prefix of these options in your commands. For example, nmcli con help, nmcli c help, nmcli connection help generate the same output.
Some of useful optional OPTIONS to get started are:
-t, terse
This mode can be used for computer script processing as you can see a terse output displaying only the values.

Example 3.1. Viewing a terse output

nmcli -t device
ens3:ethernet:connected:Profile 1
lo:loopback:unmanaged:
-f, field
This option specifies what fields can be displayed in output. For example, NAME,UUID,TYPE,AUTOCONNECT,ACTIVE,DEVICE,STATE. You can use one or more fields. If you want to use more, do not use space after comma to separate the fields.

Example 3.2. Specifying Fields in the output

~]$ nmcli -f DEVICE,TYPE device
DEVICE  TYPE
ens3    ethernet
lo      loopback
or even better for scripting: 
~]$ nmcli -t -f DEVICE,TYPE device
ens3:ethernet
lo:loopback
-p, pretty
This option causes nmcli to produce human-readable output. For example, values are aligned and headers are printed.

Example 3.3. Viewing an output in pretty mode

nmcli -p device
=====================
  Status of devices
=====================
DEVICE  TYPE      STATE      CONNECTION
--------------------------------------------------------------
ens3    ethernet  connected  Profile 1
lo      loopback  unmanaged  --
-h, help
Prints help information.
The nmcli tool has some built-in context-sensitive help:
nmcli help
This command lists the available options and object names to be used in subsequent commands.
nmcli object help
This command displays the list of available actions related to a specified object. For example, 
nmcli c help

3.3.1. Brief Selection of nmcli Examples

Example 3.4.  Checking the overall status of NetworkManager

~]$ nmcli general status
STATE      CONNECTIVITY  WIFI-HW  WIFI     WWAN-HW  WWAN
connected  full          enabled  enabled  enabled  enabled
In terse mode: 
~]$ nmcli -t -f STATE general
connected

Example 3.5.  Viewing NetworkManager logging status

~]$ nmcli general logging
  LEVEL  DOMAINS
  INFO   PLATFORM,RFKILL,ETHER,WIFI,BT,MB,DHCP4,DHCP6,PPP,WIFI_SCAN,IP4,IP6,A
UTOIP4,DNS,VPN,SHARING,SUPPLICANT,AGENTS,SETTINGS,SUSPEND,CORE,DEVICE,OLPC,
WIMAX,INFINIBAND,FIREWALL,ADSL,BOND,VLAN,BRIDGE,DBUS_PROPS,TEAM,CONCHECK,DC
B,DISPATCH

Example 3.6.  Viewing all connections

~]$ nmcli connection show
  NAME       UUID                                  TYPE      DEVICE
Profile 1  db1060e9-c164-476f-b2b5-caec62dc1b05  ethernet    ens3
ens3       aaf6eb56-73e5-4746-9037-eed42caa8a65  ethernet    --

Example 3.7. Viewing only currently active connections

~]$ nmcli connection show --active
  NAME       UUID                                  TYPE      DEVICE
Profile 1  db1060e9-c164-476f-b2b5-caec62dc1b05  ethernet     ens3

Example 3.8. Viewing only devices recognized by NetworkManager and their state

~]$ nmcli device status
DEVICE  TYPE      STATE      CONNECTION
ens3    ethernet  connected  Profile 1
lo      loopback  unmanaged  --
You can also use the following abbreviations of the nmcli commands:
Table 3.1. Abbreviations of some nmcli commands
nmcli command abbreviation  
nmcli general status nmcli g  
nmcli general logging nmcli g log  
nmcli connection show nmcli con show  
nmcli connection show --active nmcli con show -a  
nmcli device status nmcli dev  
For more examples, see the nmcli-examples(5) man page.

3.3.2. Starting and Stopping a Network Interface Using nmcli

The nmcli tool can be used to start and stop any network interface, including controllers. For example: 
nmcli con up id bond0
nmcli con up id port0
nmcli dev disconnect bond0
nmcli dev disconnect ens3

Note

The nmcli connection down command, deactivates a connection from a device without preventing the device from further auto-activation. The nmcli device disconnect command, disconnects a device and prevent the device from automatically activating further connections without manual intervention.

3.3.3. Understanding the nmcli Options

Following are some of the important nmcli property options. See the comprehensive list in the nmcli(1) man page :
connection.type
A connection type. Allowed values are: adsl, bond, bond-slave, bridge, bridge-slave, bluetooth, cdma, ethernet, gsm, infiniband, olpc-mesh, team, team-slave, vlan, wifi, wimax. Each connection type has type-specific command options. You can see the TYPE_SPECIFIC_OPTIONS list in the nmcli(1) man page. For example:
  • A gsm connection requires the access point name specified in an apn. 
    nmcli c add connection.type gsm apn access_point_name
  • A wifi device requires the service set identifier specified in a ssid. 
    nmcli c add connection.type wifi ssid My identifier
connection.interface-name
A device name relevant for the connection. 
nmcli con add connection.interface-name enp1s0 type ethernet
connection.id
A name used for the connection profile. If you do not specify a connection name, one will be generated as follows: 
connection.type -connection.interface-name
The connection.id is the name of a connection profile and should not be confused with the interface name which denotes a device (wlp61s0, ens3, em1). However, users can name the connections after interfaces, but they are not the same thing. There can be multiple connection profiles available for a device. This is particularly useful for mobile devices or when switching a network cable back and forth between different devices. Rather than edit the configuration, create different profiles and apply them to the interface as needed. The id option also refers to the connection profile name.
The most important options for nmcli commands such as show, up, down are:
id
An identification string assigned by the user to a connection profile. Id can be used in nmcli connection commands to identify a connection. The NAME field in the command output always denotes the connection id. It refers to the same connection profile name that the con-name does.
uuid
A unique identification string assigned by the system to a connection profile. The uuid can be used in nmcli connection commands to identify a connection.

3.3.4. Using the nmcli Interactive Connection Editor

The nmcli tool has an interactive connection editor. To use it: 
~]$ nmcli con edit
You will be prompted to enter a valid connection type from the list displayed. After entering a connection type you will be placed at the nmcli prompt. If you are familiar with the connection types you can add a valid connection type option to the nmcli con edit command and be taken straight to the nmcli prompt. The format is as follows for editing an existing connection profile: 
nmcli con edit [id | uuid | path] ID
For editing a new connection profile: 
nmcli con edit [type new-connection-type] [con-name new-connection-name]
Type help at the nmcli prompt to see a list of valid commands. Use the describe command to get a description of settings and their properties: 
describe setting.property
For example: 
nmcli> describe team.config

3.3.5. Creating and Modifying a Connection Profile with nmcli

A connection profile contains the connection property information needed to connect to a data source.
To create a new profile for NetworkManager using nmcli: 
nmcli c add {ARGUMENTS}
The nmcli c add accepts two different types of parameters:
Property names
the names which NetworkManager uses to describe the connection internally. The most important are:
  • connection.type 
    nmcli c add connection.type bond
  • connection.interface-name 
    nmcli c add connection.interface-name enp1s0
  • connection.id 
    nmcli c add connection.id "My Connection"
    See the nm-settings(5) man page for more information on properties and their settings.
Aliases names
the human-readable names which are translated to properties internally. The most common are:
  • type (the connection.type property) 
    nmcli c add type bond
  • ifname (the connection.interface-name property) 
    nmcli c add ifname enp1s0
  • con-name (the connection.id property) 
    nmcli c add con-name "My Connection"
In previous versions of nmcli, to create a connection required using the aliases. For example, ifname enp1s0 and con-name My Connection. A command in the following format could be used: 
nmcli c add type ethernet ifname enp1s0 con-name "My Connection"
In more recent versions, both the property names and the aliases can be used interchangeably. The following examples are all valid and equivalent: 
nmcli c add type ethernet ifname enp1s0 con-name "My Connection" ethernet.mtu 1600
nmcli c add connection.type ethernet ifname enp1s0 con-name "My Connection" ethernet.mtu 1600 
nmcli c add connection.type ethernet connection.interface-name enps1s0 connection.id  "My Connection" ethernet.mtu 1600
The arguments differ according to the connection types. Only the type argument is mandatory for all connection types and ifname is mandatory for all types except bond, team, bridge and vlan.
type type_name
connection type. For example: 
nmcli c add type bond
ifname interface_name
interface to bind the connection to. For example: 
nmcli c add ifname interface_name type ethernet
To modify one or more properties of a connection profile, use the following command: 
nmcli c modify
For example, to change the connection.id from My Connection to My favorite connection and the connection.interface-name to enp1s0, issue the command as follows: 
nmcli c modify "My Connection" connection.id "My favorite connection" connection.interface-name enp1s0

Note

It is preferable to use the property names. The aliases are used only for compatibility reasons.
In addition, to set the ethernet MTU to 1600, modify the size as follows: 
nmcli c modify "My favorite connection" ethernet.mtu 1600
To apply changes after a modified connection using nmcli, activate again the connection by entering this command: 
nmcli con up con-name
For example: 
nmcli con up My-favorite-connection 
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/16)

3.3.6. Connecting to a Network Using nmcli

To list the currently available network connections: 
~]$ nmcli con show
NAME              UUID                                  TYPE            DEVICE
Auto Ethernet     9b7f2511-5432-40ae-b091-af2457dfd988  802-3-ethernet  --
ens3              fb157a65-ad32-47ed-858c-102a48e064a2  802-3-ethernet  ens3
MyWiFi            91451385-4eb8-4080-8b82-720aab8328dd  802-11-wireless wlp61s0
Note that the NAME field in the output always denotes the connection ID (name). It is not the interface name even though it might look the same. In the second connection shown above, ens3 in the NAME field is the connection ID given by the user to the profile applied to the interface ens3. In the last connection shown, the user has assigned the connection ID MyWiFi to the interface wlp61s0.
Adding an Ethernet connection means creating a configuration profile which is then assigned to a device. Before creating a new profile, review the available devices as follows: 
~]$ nmcli device status
DEVICE  TYPE      STATE         CONNECTION
ens3    ethernet  disconnected  --
ens9    ethernet  disconnected  --
lo      loopback  unmanaged     --

3.3.7. Adding and Configuring a Dynamic Ethernet Connection with nmcli

Adding a Dynamic Ethernet Connection
To add an Ethernet configuration profile with dynamic IP configuration, allowing DHCP to assign the network configuration: 
nmcli connection add type ethernet con-name connection-name ifname interface-name
For example, to create a dynamic connection profile named my-office: 
~]$ nmcli con add type ethernet con-name my-office ifname ens3
Connection 'my-office' (fb157a65-ad32-47ed-858c-102a48e064a2) successfully added.
To open the Ethernet connection: 
~]$ nmcli con up my-office
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/5)
Review the status of the devices and connections: 
~]$ nmcli device status
DEVICE  TYPE      STATE         CONNECTION
ens3    ethernet  connected     my-office
ens9    ethernet  disconnected  --
lo      loopback  unmanaged     --
Configuring a Dynamic Ethernet Connection
To change the host name sent by a host to a DHCP server, modify the dhcp-hostname property: 
~]$ nmcli con modify my-office my-office ipv4.dhcp-hostname host-name ipv6.dhcp-hostname host-name
To change the IPv4 client ID sent by a host to a DHCP server, modify the dhcp-client-id property: 
~]$ nmcli con modify my-office my-office ipv4.dhcp-client-id client-ID-string
There is no dhcp-client-id property for IPv6, dhclient creates an identifier for IPv6. See the dhclient(8) man page for details.
To ignore the DNS servers sent to a host by a DHCP server, modify the ignore-auto-dns property: 
~]$ nmcli con modify my-office my-office ipv4.ignore-auto-dns yes ipv6.ignore-auto-dns yes
See the nm-settings(5) man page for more information on properties and their settings.

Example 3.9. Configuring a Dynamic Ethernet Connection Using the Interactive Editor

To configure a dynamic Ethernet connection using the interactive editor: 
~]$ nmcli con edit type ethernet con-name ens3

===| nmcli interactive connection editor |===

Adding a new '802-3-ethernet' connection

Type 'help' or '?' for available commands.
Type 'describe [<setting>.<prop>]' for detailed property description.

You may edit the following settings: connection, 802-3-ethernet (ethernet), 802-1x, ipv4, ipv6, dcb
nmcli> describe ipv4.method

=== [method] ===
[NM property description]
IPv4 configuration method.  If 'auto' is specified then the appropriate automatic method (DHCP, PPP, etc) is used for the interface and most other properties can be left unset.  If 'link-local' is specified, then a link-local address in the 169.254/16 range will be assigned to the interface.  If 'manual' is specified, static IP addressing is used and at least one IP address must be given in the 'addresses' property.  If 'shared' is specified (indicating that this connection will provide network access to other computers) then the interface is assigned an address in the 10.42.x.1/24 range and a DHCP and forwarding DNS server are started, and the interface is NAT-ed to the current default network connection.  'disabled' means IPv4 will not be used on this connection.  This property must be set.

nmcli> set ipv4.method auto
nmcli> save
Saving the connection with 'autoconnect=yes'. That might result in an immediate activation of the connection.
Do you still want to save? [yes] yes
Connection 'ens3' (090b61f7-540f-4dd6-bf1f-a905831fc287) successfully saved.
nmcli> quit
~]$
The default action is to save the connection profile as persistent. If required, the profile can be held in memory only, until the next restart, by means of the save temporary command.

3.3.8. Adding and Configuring a Static Ethernet Connection with nmcli

Adding a Static Ethernet Connection
To add an Ethernet connection with static IPv4 configuration: 
nmcli connection add type ethernet con-name connection-name ifname interface-name ip4 address gw4 address
IPv6 address and gateway information can be added using the ip6 and gw6 options.
For example, to create a static Ethernet connection with only IPv4 address and gateway: 
~]$ nmcli con add type ethernet con-name test-lab ifname ens9 ip4 10.10.10.10/24 \
gw4 10.10.10.254
Optionally, at the same time specify IPv6 address and gateway for the device: 
~]$ nmcli con add type ethernet con-name test-lab ifname ens9 ip4 10.10.10.10/24 \
gw4 10.10.10.254 ip6 abbe::cafe gw6 2001:db8::1
Connection 'test-lab' (05abfd5e-324e-4461-844e-8501ba704773) successfully added.
To set two IPv4 DNS server addresses: 
~]$ nmcli con mod test-lab ipv4.dns "8.8.8.8 8.8.4.4"
Note that this will replace any previously set DNS servers. To set two IPv6 DNS server addresses: 
~]$ nmcli con mod test-lab ipv6.dns "2001:4860:4860::8888 2001:4860:4860::8844"
Note that this will replace any previously set DNS servers. Alternatively, to add additional DNS servers to any previously set, use the + prefix: 
~]$ nmcli con mod test-lab +ipv4.dns "8.8.8.8 8.8.4.4"
~]$ nmcli con mod test-lab +ipv6.dns "2001:4860:4860::8888 2001:4860:4860::8844"
To open the new Ethernet connection: 
~]$ nmcli con up test-lab ifname ens9
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/6)
Review the status of the devices and connections: 
~]$ nmcli device status
DEVICE  TYPE      STATE      CONNECTION
ens3    ethernet  connected  my-office
ens9    ethernet  connected  test-lab
lo      loopback  unmanaged  --
To view detailed information about the newly configured connection, issue a command as follows: 
~]$ nmcli -p con show test-lab
===============================================================================
                     Connection profile details (test-lab)
===============================================================================
connection.id:                          test-lab
connection.uuid:                        05abfd5e-324e-4461-844e-8501ba704773
connection.interface-name:              ens9
connection.type:                        802-3-ethernet
connection.autoconnect:                 yes
connection.timestamp:                   1410428968
connection.read-only:                   no
connection.permissions:
connection.zone:                        --
connection.master:                      --
connection.slave-type:                  --
connection.secondaries:
connection.gateway-ping-timeout:        0
[output truncated]
The use of the -p, --pretty option adds a title banner and section breaks to the output.

Example 3.10. Configuring a Static Ethernet Connection Using the Interactive Editor

To configure a static Ethernet connection using the interactive editor: 
~]$ nmcli con edit type ethernet con-name ens3

===| nmcli interactive connection editor |===

Adding a new '802-3-ethernet' connection

Type 'help' or '?' for available commands.
Type 'describe [>setting<.>prop<]' for detailed property description.

You may edit the following settings: connection, 802-3-ethernet (ethernet), 802-1x, ipv4, ipv6, dcb
nmcli> set ipv4.addresses 192.168.122.88/24
Do you also want to set 'ipv4.method' to 'manual'? [yes]: yes
nmcli>
nmcli> save temporary
Saving the connection with 'autoconnect=yes'. That might result in an immediate activation of the connection.
Do you still want to save? [yes] no
nmcli> save
Saving the connection with 'autoconnect=yes'. That might result in an immediate activation of the connection.
Do you still want to save? [yes] yes
Connection 'ens3' (704a5666-8cbd-4d89-b5f9-fa65a3dbc916) successfully saved.
nmcli> quit
~]$
The default action is to save the connection profile as persistent. If required, the profile can be held in memory only, until the next restart, by means of the save temporary command.
NetworkManager will set its internal parameter connection.autoconnect to yes. NetworkManager will also write out settings to /etc/sysconfig/network-scripts/ifcfg-my-office where the corresponding BOOTPROTO will be set to none and ONBOOT to yes.
Note that manual changes to the ifcfg file will not be noticed by NetworkManager until the interface is next brought up. See Section 2.7, “Using NetworkManager with sysconfig files”, Section 3.5, “Configuring IP Networking with ifcfg Files” for more information on using configuration files.

3.3.9. Locking a Profile to a Specific Device Using nmcli

To lock a profile to a specific interface device: 
nmcli connection add type ethernet con-name connection-name ifname interface-name
To make a profile usable for all compatible Ethernet interfaces: 
nmcli connection add type ethernet con-name connection-name ifname "*"
Note that you have to use the ifname argument even if you do not want to set a specific interface. Use the wildcard character * to specify that the profile can be used with any compatible device.
To lock a profile to a specific MAC address: 
nmcli connection add type ethernet con-name "connection-name" ifname "*" mac 00:00:5E:00:53:00

3.3.10. Adding a Wi-Fi Connection with nmcli

To view the available Wi-Fi access points: 
~]$ nmcli dev wifi list
  SSID            MODE  CHAN  RATE     SIGNAL  BARS  SECURITY
  FedoraTest     Infra  11    54 MB/s  98      ▂▄▆█  WPA1
  Red Hat Guest  Infra  6     54 MB/s  97      ▂▄▆█  WPA2
  Red Hat        Infra  6     54 MB/s  77      ▂▄▆_  WPA2 802.1X
* Red Hat        Infra  40    54 MB/s  66      ▂▄▆_  WPA2 802.1X
  VoIP           Infra  1     54 MB/s  32      ▂▄__  WEP
  MyCafe         Infra  11    54 MB/s  39      ▂▄__  WPA2
To create a Wi-Fi connection profile with static IP configuration, but allowing automatic DNS address assignment: 
~]$ nmcli con add con-name MyCafe ifname wlp61s0 type wifi ssid MyCafe \
ip4 192.168.100.101/24 gw4 192.168.100.1
To set a WPA2 password, for example “caffeine”: 
~]$ nmcli con modify MyCafe wifi-sec.key-mgmt wpa-psk
~]$ nmcli con modify MyCafe wifi-sec.psk caffeine
See the Red Hat Enterprise Linux 7 Security Guide for information on password security.
To change Wi-Fi state: 
~]$ nmcli radio wifi [on | off ]
Changing a Specific Property Using nmcli
To check a specific property, for example mtu: 
~]$ nmcli connection show id 'MyCafe' | grep mtu
802-11-wireless.mtu:                     auto
To change the property of a setting: 
~]$ nmcli connection modify id 'MyCafe' 802-11-wireless.mtu 1350
To verify the change: 
~]$ nmcli connection show id 'MyCafe' | grep mtu
802-11-wireless.mtu:                     1350
Note that NetworkManager refers to parameters such as 802-3-ethernet and 802-11-wireless as the setting, and mtu as a property of the setting. See the nm-settings(5) man page for more information on properties and their settings.

3.3.11. Configuring NetworkManager to Ignore Certain Devices

By default, NetworkManager manages all devices except the lo (loopback) device. However, you can set certain devices as unmanaged to configure that NetworkManager ignores these devices. With this setting, you can manually manage these devices, for example, using a script.
3.3.11.1. Permanently Configuring a Device as Unmanaged in NetworkManager
You can configure devices as unmanaged based on several criteria, such as the interface name, MAC address, or device type. This procedure describes how to permanently set the enp1s0 interface as unmanaged in NetworkManager.
To temporarily configure network devices as unmanaged, see Section 3.3.11.2, “Temporarily Configuring a Device as Unmanaged in NetworkManager”.
Procedure
  1. Optional: Display the list of devices to identify the device you want to set as unmanaged: 
    # nmcli device status
DEVICE  TYPE      STATE         CONNECTION
enp1s0  ethernet  disconnected  --
...
  2. Create the /etc/NetworkManager/conf.d/99-unmanaged-devices.conf file with the following content: 
    [keyfile]
unmanaged-devices=interface-name:enp1s0
    To set multiple devices as unmanaged, separate the entries in the unmanaged-devices parameter with semicolon: 
    [keyfile]
unmanaged-devices=interface-name:interface_1;interface-name:interface_2;...
  3. Reload the NetworkManager service: 
    # systemctl reload NetworkManager
Verification Steps
  • Display the list of devices: 
    # nmcli device status
DEVICE  TYPE      STATE      CONNECTION
enp1s0  ethernet  unmanaged  --
...
    The unmanaged state next to the enp1s0 device indicates that NetworkManager does not manage this device.
Additional Resources
For a list of criteria you can use to configure devices as unmanaged and the corresponding syntax, see the Device List Format section in the NetworkManager.conf(5) man page.
3.3.11.2. Temporarily Configuring a Device as Unmanaged in NetworkManager
You can configure devices as unmanaged based on several criteria, such as the interface name, MAC address, or device type. This procedure describes how to temporarily set the enp1s0 interface as unmanaged in NetworkManager.
Use this method, for example, for testing purposes. To permanently configure network devices as unmanaged, see Section 3.3.11.1, “Permanently Configuring a Device as Unmanaged in NetworkManager”.
Procedure
  1. Optional: Display the list of devices to identify the device you want to set as unmanaged: 
    # nmcli device status
DEVICE  TYPE      STATE         CONNECTION
enp1s0  ethernet  disconnected  --
...
  2. Set the enp1s0 device to the unmanaged state: 
    # nmcli device set enp1s0 managed no
Verification Steps
  • Display the list of devices: 
    # nmcli device status
DEVICE  TYPE      STATE      CONNECTION
enp1s0  ethernet  unmanaged  --
...
    The unmanaged state next to the enp1s0 device indicates that NetworkManager does not manage this device.
Additional Resources
For a list of criteria you can use to configure devices as unmanaged and the corresponding syntax, see the Device List Format section in the NetworkManager.conf(5) man page.

3.4.  Configuring IP Networking with GNOME GUI

In Red Hat Enterprise Linux 7, NetworkManager does not have its own graphical user interface (GUI). The network connection icon on the top right of the desktop is provided as part of the GNOME Shell and the Network settings configuration tool is provided as part of the new GNOME control-center GUI which supports the wired, wireless, vpn connections. The nm-connection-editor is the main tool for GUI configuration. Besides control-center's features, it also applies the functionality which is not provided by the GNOME control-center such as configuring bond, team, bridge connections. In this section, you can configure a network interface using:
  • the GNOME control-center application
  • the GNOME nm-connection-editor application

3.4.1. Connecting to a Network Using the control-center GUI

There are two ways to access the Network settings window of the control-center application:
  • Press the Super key to enter the Activities Overview, type Settings and then press Enter. Then, select the Network tab on the left-hand side, and the Network settings tool appears. Proceed to the section called “Configuring New Connections with control-center”.
  • Click on the GNOME Shell network connection icon in the top right-hand corner of the screen to open its menu.
    Network Configuration using the control-center application

    Figure 3.5. Network Configuration using the control-center application

When you click on the GNOME Shell network connection icon, you are presented with:
  • A list of categorized networks you are currently connected to (such as Wired and Wi-Fi).
  • A list of all Available Networks that NetworkManager has detected.
  • Options for connecting to any configured Virtual Private Networks (VPNs)
    and
  • An option for selecting the Network Settings menu entry.
If you are connected to a network, this is indicated by a black bullet on the left of the connection name.
If you click on Network Settings, the Network settings tool appears. Proceed to the section called “Configuring New Connections with control-center”.

3.4.2. Configuring New and Editing Existing Connections Using a GUI

As a system administrator, you can configure a network connection. This enables users to apply or change settings of an interface. For doing that, you can use one of the following two ways:
  • the GNOME control-center application
  • the GNOME nm-connection-editor application
3.4.2.1. Configuring New and Editing Existing Connections Using control-center
You can create and configure a network connection using the GNOME control-center application.
Configuring New Connections with control-center
To configure a new wired, wireless, vpn connection using the control-center application, proceed as follows:
  1. Press the Super key to enter the Activities Overview, type Settings and then press Enter. Then, select the Network tab on the left-hand side. The Network settings tool appears on the right-hand side menu:
    Opening the Network Settings Window

    Figure 3.6. Opening the Network Settings Window

  2. Click the plus button to add a new connection.
    To configure:
    For Wi-Fi connections, click the Wi-fi entry in the Settings menu and proceed to Section 3.4.7, “Configuring a Wi-Fi Connection with a GUI”
Editing an Existing Connection with control-center
Clicking on the gear wheel icon of an existing connection profile in the Network settings window opens the Details window, from where you can perform most network configuration tasks such as IP addressing, DNS, and routing configuration.
Configure Networks Using the Network Connection Details Window

Figure 3.7. Configure Networks Using the Network Connection Details Window

For any connection type you add or configure, you can choose NetworkManager to connect to that network automatically when it is available. For doing that, select Connect automatically to cause NetworkManager to auto-connect to the connection whenever NetworkManager detects that it is available. Clear the check box if you do not want NetworkManager to connect automatically. If the check box is clear, you will have to select that connection manually in the network connection icon's menu to cause it to connect.
To make a connection available to other users, select the Make available to other users check box.
To apply changes after a connection modification, you can click the Apply button in the top right-hand corner of the connection window.
You can delete a connection by clicking the Remove Connection Profile red box.
3.4.2.2. Configuring New and Editing Existing Connections Using nm-connection-editor
Using the nm-connection-editor GUI application, you can configure any connection you want with additional features than control-center provides. In addition, nm-connection-editor applies the functionality which is not provided by the GNOME control-center such as configuring bond, bridge, VLAN, team connections.
Configuring a New Connection with nm-connection-editor
To add a new connection type using nm-connection-editor:
Procedure
  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
    The Network Connections window appears.
  2. Click the plus button to choose a connection type:
    Adding a connection type using nm-connection-editor

    Figure 3.8. Adding a connection type using nm-connection-editor

    Choosing a connection type with nm-connection-editor

    Figure 3.9.  Choosing a connection type with nm-connection-editor

    To create and configure:
Editing an Existing Connection with nm-connection-editor
For an existing connection type, click the gear wheel icon from the Network Connections dialog, see the section called “Configuring a New Connection with nm-connection-editor”.

3.4.3. Common Configuration Options Using nm-connection-editor

If you use the nm-connection-editor utility, there are five common configuration options to the most connection types (ethernet, wifi, mobile broadband, DSL) following the procedure below:
Procedure
  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
    The Network Connections window appears. Click the plus button to choose a connection type or the gear wheel icon to edit an existing connection.
  2. Select the General tab in the Editing dialog:
    Configuration options in nm-connection-editor

    Figure 3.10. Configuration options in nm-connection-editor

  • Connection name — Enter a descriptive name for your network connection. This name is used to list this connection in the menu of the Network window.
  • Connection priority for auto-activation — If the connection is set to autoconnect, the number is activated (0 by default). The higher number means higher priority.
  • Automatically connect to this network when it is available — Select this box if you want NetworkManager to auto-connect to this connection when it is available. See the section called “Editing an Existing Connection with control-center” for more information.
  • All users may connect to this network — Select this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 3.4.5, “Managing System-wide and Private Connection Profiles with a GUI” for details.
  • Automatically connect to VPN when using this connection — Select this box if you want NetworkManager to auto-connect to a VPN connection when it is available. Select the VPN from the drop-down menu.
  • Firewall Zone — Select the firewall zone from the drop-down menu. See the Red Hat Enterprise Linux 7 Security Guide for more information on firewall zones.

Note

For the VPN connection type, only three of the above configuration options are available: Connection name, All users may connect to this network and Firewall Zone.

3.4.4. Connecting to a Network Automatically with a GUI

For any connection type you add or configure, you can choose whether you want NetworkManager to try to connect to that network automatically when it is available. You can use one of the following ways:
  • the GNOME control-center application
  • the GNOME nm-connection-editor application
3.4.4.1. Connecting to a Network Automatically with control-center
You can connect to a network automatically using control-center:
Procedure
  1. Press the Super key to enter the Activities Overview, type Settings and then press Enter. Then, select the Network tab on the left-hand side. The Network settings tool appears on the right-hand side menu, see the section called “Configuring New Connections with control-center”.
  2. Select the network interface from the right-hand-side menu.
  3. Click on the gear wheel icon of a connection profile on the right-hand side menu. The Network details window appears.
  4. Select the Details menu entry, see the section called “Editing an Existing Connection with control-center”.
  5. Select Connect automatically to cause NetworkManager to auto-connect to the connection whenever NetworkManager detects that it is available. Clear the check box if you do not want NetworkManager to connect automatically. If the check box is clear, you will have to select that connection manually in the network connection icon's menu to cause it to connect.
3.4.4.2. Connecting to a Network Automatically with nm-connection-editor
You can also use the GNOME nm-connection-editor application for connecting to a network automatically. For doing that, follow the procedure descibed in Section 3.4.3, “Common Configuration Options Using nm-connection-editor”, and check the Automatically connect to this network when it is available check box in the General tab.

3.4.5. Managing System-wide and Private Connection Profiles with a GUI

NetworkManager stores all connection profiles. A profile is a named collection of settings that can be applied to an interface. NetworkManager stores these connection profiles for system-wide use (system connections), as well as all user connection profiles. Access to the connection profiles is controlled by permissions which are stored by NetworkManager. See the nm-settings(5) man page for more information on the connection settings permissions property. You can control access to a connection profile using the following graphical user interface tools:
  • the nm-connection-editor application
  • the control-center application
3.4.5.1. Managing Permissions for a Connection Profile with nm-connection-editor
To create a connection available to all users on the system, follow the procedure descibed in Section 3.4.3, “Common Configuration Options Using nm-connection-editor”, and check the All users may connect to this network check box in the General tab.
3.4.5.2. Managing Permissions for a Connection Profile with control-center
To make a connection available to other users, follow the procedure described in the section called “Editing an Existing Connection with control-center”, and select the Make available to other users check box in the GNOME control-center Network settings Details window.
Conversely, clear the Make available to other users check box to make the connection user-specific instead of system-wide.

Note

Depending on the system's policy, you may need root privileges on the system in order to change whether a connection is user-specific or system-wide.
NetworkManager's default policy is to allow all users to create and modify system-wide connections. Profiles that are available at boot time cannot be private because they will not be visible until the user logs in. For example, if a user creates a connection profile user-em2 with the Connect Automatically check box selected but with the Make available to other users not selected, then the connection will not be available at boot time.
To restrict connections and networking, there are two options which can be used alone or in combination:
  • Clear the Make available to other users check box, which changes the connection to be modifiable and usable only by the user doing the changing.
  • Use the polkit framework to restrict permissions of general network operations on a per-user basis.
The combination of these two options provides fine-grained security and control over networking. See the polkit(8) man page for more information on polkit.
Note that VPN connections are always created as private-per-user, since they are assumed to be more private than a Wi-Fi or Ethernet connection.

3.4.6. Configuring a Wired (Ethernet) Connection with a GUI

You can configure a wired connection using GUI in two ways:
  • the control-center application
  • the nm-connection-editor application
3.4.6.1. Configuring a Wired Connection Using control-center
Procedure
  1. Press the Super key to enter the Activities Overview, type Settings and then press Enter. Then, select the Network menu entry on the left-hand side, and the Network settings tool appears, see the section called “Configuring New Connections with control-center”.
  2. Select the Wired network interface if it is not already highlighted.
    The system creates and configures a single wired connection profile called Wired by default. A profile is a named collection of settings that can be applied to an interface. More than one profile can be created for an interface and applied as needed. The default profile cannot be deleted but its settings can be changed.
  3. Edit the default Wired profile by clicking the gear wheel icon.
Basic Configuration Options
You can see the following configuration settings in the Wired dialog, by selecting the Identity menu entry:
Basic Configuration options of a Wired Connection

Figure 3.11.  Basic Configuration options of a Wired Connection

  • Name — Enter a descriptive name for your network connection. This name will be used to list this connection in the menu of the Network window.
  • MAC Address — Select the MAC address of the interface this profile must be applied to.
  • Cloned Address — If required, enter a different MAC address to use.
  • MTU — If required, enter a specific maximum transmission unit (MTU) to use. The MTU value represents the size in bytes of the largest packet that the link layer will transmit. This value defaults to 1500 and does not generally need to be specified or changed.
Making Further Wired Configurations
You can further configure an existing connection in the editing dialog.
To configure:
Saving Your New (or Modified) Wired Connection
Once you have finished editing your wired connection, click the Apply button to save your customized configuration. If the profile was in use while being edited, restart the connection to make NetworkManager apply the changes. If the profile is OFF, set it to ON or select it in the network connection icon's menu. See Section 3.4.1, “Connecting to a Network Using the control-center GUI” for information on using your new or altered connection.
Creating a New Wired Connection
To create a new wired connection profile, click the plus button, see the section called “Configuring New Connections with control-center”.
When you add a new connection by clicking the plus button, NetworkManager creates a new configuration file for that connection and then opens the same dialog that is used for editing an existing connection, see the section called “Editing an Existing Connection with control-center”. The difference between these dialogs is that an existing connection profile has a Details menu entry.
3.4.6.2. Configuring a Wired Connection with nm-connection-editor
The nm-connection-editor GUI application provides more configuration options than the control-center GUI application. To configure a wired connection using nm-connection-editor:
  1. Enter the nm-connection-editor in a terminal. 
    ~]$ nm-connection-editor
    The Network Connections window appears.
  2. Select the ethernet connection you want to edit and click the gear wheel icon:
    Edit a wired connection

    Figure 3.12. Edit a wired connection

    The Editing dialog appears.

3.4.7. Configuring a Wi-Fi Connection with a GUI

This section explains how to use NetworkManager to configure a Wi-Fi (also known as wireless or 802.11a/b/g/n) connection to an Access Point. An Access Point is a device that allows wireless devices to connect to a network.
To configure a mobile broadband (such as 3G) connection, see Section 3.4.9, “Configuring a Mobile Broadband Connection with a GUI”.
Connecting Quickly to an Available Access Point
Procedure
  1. Click on the network connection icon to activate the network connection icon's menu, see Section 3.4.1, “Connecting to a Network Using the control-center GUI”.
  2. Locate the Service Set Identifier (SSID) of the access point in the list of Wi-Fi networks.
  3. Click on the SSID of the network. A padlock symbol indicates the access point requires authentication. If the access point is secured, a dialog prompts you for an authentication key or password.
    NetworkManager tries to auto-detect the type of security used by the access point. If there are multiple possibilities, NetworkManager guesses the security type and presents it in the Wi-Fi security drop-down menu.
    • For WPA-PSK security (WPA with a passphrase) no choice is necessary.
    • For WPA Enterprise (802.1X) you have to specifically select the security, because that cannot be auto-detected.
      Note that if you are unsure, try connecting to each type in turn.
  4. Enter the key or passphrase in the Password field. Certain password types, such as a 40-bit WEP or 128-bit WPA key, are invalid unless they are of a requisite length. The Connect button will remain inactive until you enter a key of the length required for the selected security type. To learn more about wireless security, see Section 5.2, “Configuring 802.1X Security”.
If NetworkManager connects to the access point successfully, the network connection icon will change into a graphical indicator of the wireless connection's signal strength.
You can also edit the settings for one of these auto-created access point connections just as if you had added it yourself. The Wi-Fi page of the Network window has a History button. Clicking it reveals a list of all the connections you have ever tried to connect to. See the section called “Editing an Existing Wi-Fi Connection”
Connecting to a Hidden Wi-Fi Network
All access points have a Service Set Identifier (SSID) to identify them. However, an access point may be configured not to broadcast its SSID, in which case it is hidden, and will not show up in NetworkManager's list of Available networks. You can still connect to a wireless access point that is hiding its SSID as long as you know its SSID, authentication method, and secrets. To connect to a hidden wireless network:
Procedure
  1. Press the Super key to enter the Activities Overview, type Settings and then press Enter. Then, select the Wi-Fi menu entry on the left-hand side.
  2. Select Connect to Hidden Network. There are two options:
    • If you have connected to the hidden network before:
      1. Use the Connection drop-down to select the network.
      2. Click Connect.
    • If not, proceed as follows:
      1. Leave the Connection drop-down as New.
      2. Enter the SSID of the hidden network.
      3. Select its Wi-Fi security method.
      4. Enter the correct authentication secrets.
      5. Click Connect.
For more information on wireless security settings, see Section 5.2, “Configuring 802.1X Security”.
Configuring a New Wi-Fi Connection
Procedure
  1. Select the Wi-Fi menu entry of Settings.
  2. Click the Wi-Fi connection name that you want to connect to (by default, the same as the SSID).
    • If the SSID is not in range, see the section called “Connecting to a Hidden Wi-Fi Network” for more information.
    • If the SSID is in range, click the Wi-Fi connection profile on the right-hand side menu. A padlock symbol indicates a key or password is required. If requested, enter the authentication details.
Editing an Existing Wi-Fi Connection
You can edit an existing connection that you have tried or succeeded in connecting to in the past.
Procedure
  1. Press the Super key to enter the Activities Overview, type Settings and press Enter.
  2. Select Wi-Fi from the left-hand-side menu entry.
  3. Select the gear wheel icon to the right of the Wi-Fi connection name that you want to edit, and the editing connection dialog appears. Note that if the network is not currently in range, click History to display past connections. The Details window shows the connection details.
Basic Configuration Options for a Wi-Fi Connection
To edit a Wi-Fi connection's settings, select Identity from the editing connection dialog. The following settings are available:
Basic Configuration Options for a Wi-Fi Connection

Figure 3.13. Basic Configuration Options for a Wi-Fi Connection

SSID
The Service Set Identifier (SSID) of the access point (AP).
BSSID
The Basic Service Set Identifier (BSSID) is the MAC address, also known as a hardware address, of the specific wireless access point you are connecting to when in Infrastructure mode. This field is blank by default, and you are able to connect to a wireless access point by SSID without having to specify its BSSID. If the BSSID is specified, it will force the system to associate to a specific access point only.
For ad-hoc networks, the BSSID is generated randomly by the mac80211 subsystem when the ad-hoc network is created. It is not displayed by NetworkManager
MAC address
Select the MAC address, also known as a hardware address, of the Wi-Fi interface to use.
A single system could have one or more wireless network adapters connected to it. The MAC address field therefore allows you to associate a specific wireless adapter with a specific connection (or connections).
Cloned Address
A cloned MAC address to use in place of the real hardware address. Leave blank unless required.
The following settings are common to the most connection types:
Making Further Wi-Fi Configurations
You can further configure an existing connection in the editing dialog.
To configure:
Saving Your New (or Modified) Connection
Once you have finished editing the wireless connection, click the Apply button to save your configuration. Given a correct configuration, you can connect to your modified connection by selecting it from the network connection icon's menu. See Section 3.4.1, “Connecting to a Network Using the control-center GUI” for details on selecting and connecting to a network.

3.4.8. Configuring a VPN Connection with a GUI

IPsec, provided by Libreswan, is the preferred method for creating a VPN. Libreswan is an open-source, user-space IPsec implementation for VPN. Configuring an IPsec VPN using the command line is documented in the Red Hat Enterprise Linux 7 Security Guide.
3.4.8.1. Establishing a VPN Connection with control-center
IPsec, provided by Libreswan, is the preferred method for creating a VPN in Red Hat Enterprise Linux 7. For more information, see Section 3.4.8, “Configuring a VPN Connection with a GUI”.
The GNOME graphical user interface tool described below requires the NetworkManager-libreswan-gnome package. To install the package, run the following command as root: 
~]# yum install NetworkManager-libreswan-gnome
See Red Hat Enterprise Linux System Administrator's Guide for more information on how to install new packages in Red Hat Enterprise Linux.
Establishing a Virtual Private Network (VPN) enables communication between your Local Area Network (LAN), and another, remote LAN. This is done by setting up a tunnel across an intermediate network such as the Internet. The VPN tunnel that is set up typically uses authentication and encryption. After successfully establishing a VPN connection using a secure tunnel, a VPN router or gateway performs the following actions upon the packets you transmit:
  1. it adds an Authentication Header for routing and authentication purposes;
  2. it encrypts the packet data; and,
  3. it encloses the data in packets according to the Encapsulating Security Payload (ESP) protocol, which constitutes the decryption and handling instructions.
The receiving VPN router strips the header information, decrypts the data, and routes it to its intended destination (either a workstation or other node on a network). Using a network-to-network connection, the receiving node on the local network receives the packets already decrypted and ready for processing. The encryption and decryption process in a network-to-network VPN connection is therefore transparent to clients.
Because they employ several layers of authentication and encryption, VPNs are a secure and effective means of connecting multiple remote nodes to act as a unified intranet.
Adding a New IPsec VPN Connection
Procedure
  1. Press the Super key to enter the Activities Overview, type Settings and press Enter. Then, select the Network menu entry and the Network settings tool appears, see the section called “Configuring New Connections with control-center”.
  2. Click the plus button in the VPN entry.
  3. The Add VPN window appears. For manually configuration, select IPsec based VPN.
    Configuring VPN on IPsec mode

    Figure 3.14.  Configuring VPN on IPsec mode

  4. In the Identity configuration form, you can specify the fields in the General and Advanced sections:
    General and Advanced sections

    Figure 3.15. General and Advanced sections

  • In General section, you can specify:
Gateway
The name or IP address of the remote VPN gateway.
User name
If required, enter the user name associated with the VPN user's identity for authentication.
User password
If required, enter the password associated with the VPN user's identity for authentication.
Group name
The name of a VPN group configured on the remote gateway. In case it is blank, the IKEv1 Main mode is used instead of the default Aggressive mode.
Secret
It is a pre-shared key which is used to initialize the encryption before the user's authentication. If required, enter the password associated with the group name.
  • The following configuration settings are available under the Advanced section:
Phase1 Algorithms
If required, enter the algorithms to be used to authenticate and set up an encrypted channel.
Phase2 Algorithms
If required, enter the algorithms to be used for the IPsec negotiations.
Domain
If required, enter the Domain Name.

Note

Configuring an IPsec VPN without using NetworkManager, see Section 3.4.8, “Configuring a VPN Connection with a GUI”.
Editing an Existing VPN Connection
Procedure
  1. Press the Super key to enter the Activities Overview, type Settings and press Enter. Then, select the Network menu entry and the Network settings tool appears, see the section called “Configuring New Connections with control-center”.
  2. Select the VPN connection you want to edit and click the gear wheel icon and edit the General and Advanced sections, see Section 3.4.8.1, “Establishing a VPN Connection with control-center”.
Saving Your New (or Modified) Connection and Making Further Configurations
Once you have finished editing your new VPN connection, click the Save button to save your customized configuration. If the profile was in use while being edited, power cycle the connection to make NetworkManager apply the changes. If the profile is OFF, set it to ON or select it in the network connection icon's menu. See Section 3.4.1, “Connecting to a Network Using the control-center GUI” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network window and clicking Configure to return to the Editing dialog.
Then, to configure:
3.4.8.2. Configuring a VPN Connection with nm-connection-editor
You can also use nm-connection-editor to add and configure a VPN connection. For doing that, proceed as follows:
Procedure
  1. Enter nm-connection-editor in a terminal. The Network Connections window appears, see Section 3.4.3, “Common Configuration Options Using nm-connection-editor”.
  2. Click the plus button. The Choose a Connection Type menu opens.
  3. Select from the VPN menu entry, the IPsec based VPN option.
  4. Click Create to open the Editing dialog and proceed to the section called “Adding a New IPsec VPN Connection” to edit the General and Advanced sections.

3.4.9. Configuring a Mobile Broadband Connection with a GUI

You can use NetworkManager's mobile broadband connection abilities to connect to the following 2G and 3G services:
  • 2G — GPRS (General Packet Radio Service), EDGE (Enhanced Data Rates for GSM Evolution), or CDMA (Code Division Multiple Access).
  • 3G — UMTS (Universal Mobile Telecommunications System), HSPA (High Speed Packet Access), or EVDO (EVolution Data-Only).
Your computer must have a mobile broadband device (modem), which the system has discovered and recognized, in order to create the connection. Such a device may be built into your computer (as is the case on many notebooks and netbooks), or may be provided separately as internal or external hardware. Examples include PC card, USB Modem or Dongle, mobile or cellular telephone capable of acting as a modem.
3.4.9.1. Configuring a Mobile Broadband Connection with nm-connection-editor
You can configure a mobile broadband connection using the GNOME nm-connection-editor.
Adding a New Mobile Broadband Connection
Procedure
  1. Enter nm-connection-editor in a terminal. The Network Connections window appears, see Section 3.4.3, “Common Configuration Options Using nm-connection-editor”.
  2. Click the plus button. The Choose a Connection Type menu opens.
  3. Select the Mobile Broadband menu entry.
  4. Click Create to open the Set up a Mobile Broadband Connection assistant.
  5. Under Create a connection for this mobile broadband device, choose the 2G- or 3G-capable device you want to use with the connection. If the drop-down menu is inactive, this indicates that the system was unable to detect a device capable of mobile broadband. In this case, click Cancel, ensure that you do have a mobile broadband-capable device attached and recognized by the computer and then retry this procedure. Click the Continue button.
  6. Select the country where your service provider is located from the list and click the Continue button.
  7. Select your provider from the list or enter it manually. Click the Continue button.
  8. Select your payment plan from the drop-down menu and confirm the Access Point Name (APN) is correct. Click the Continue button.
  9. Review and confirm the settings and then click the Apply button.
  10. Edit the mobile broadband-specific settings by referring to the section called “Configuring the Mobile Broadband Tab”
Editing an Existing Mobile Broadband Connection
Procedure
  1. Enter nm-connection-editor in a terminal. The Network Connections window appears.
  2. Select the Mobile Broadband tab.
  3. Select the connection you want to edit and click the gear wheel icon. See Section 3.4.3, “Common Configuration Options Using nm-connection-editor” for more information.
  4. Edit the mobile broadband-specific settings by referring to the section called “Configuring the Mobile Broadband Tab”
Configuring the Mobile Broadband Tab
If you have already added a new mobile broadband connection using the assistant (see the section called “Adding a New Mobile Broadband Connection” for instructions), you can edit the Mobile Broadband tab to disable roaming if home network is not available, assign a network ID, or instruct NetworkManager to prefer a certain technology (such as 3G or 2G) when using the connection.
Number
The number that is dialed to establish a PPP connection with the GSM-based mobile broadband network. This field may be automatically populated during the initial installation of the broadband device. You can usually leave this field blank and enter the APN instead.
Username
Enter the user name used to authenticate with the network. Some providers do not provide a user name, or accept any user name when connecting to the network.
Password
Enter the password used to authenticate with the network. Some providers do not provide a password, or accept any password.
APN
Enter the Access Point Name (APN) used to establish a connection with the GSM-based network. Entering the correct APN for a connection is important because it often determines:
  • how the user is billed for their network usage;
  • whether the user has access to the Internet, an intranet, or a subnetwork.
Network ID
Entering a Network ID causes NetworkManager to force the device to register only to a specific network. This can be used to ensure the connection does not roam when it is not possible to control roaming directly.
Type
Any — The default value of Any leaves the modem to select the fastest network.
3G (UMTS/HSPA) — Force the connection to use only 3G network technologies.
2G (GPRS/EDGE) — Force the connection to use only 2G network technologies.
Prefer 3G (UMTS/HSPA) — First attempt to connect using a 3G technology such as HSPA or UMTS, and fall back to GPRS or EDGE only upon failure.
Prefer 2G (GPRS/EDGE) — First attempt to connect using a 2G technology such as GPRS or EDGE, and fall back to HSPA or UMTS only upon failure.
Allow roaming if home network is not available
Uncheck this box if you want NetworkManager to terminate the connection rather than transition from the home network to a roaming one, thereby avoiding possible roaming charges. If the box is checked, NetworkManager will attempt to maintain a good connection by transitioning from the home network to a roaming one, and vice versa.
PIN
If your device's SIM (Subscriber Identity Module) is locked with a PIN (Personal Identification Number), enter the PIN so that NetworkManager can unlock the device. NetworkManager must unlock the SIM if a PIN is required in order to use the device for any purpose.
CDMA and EVDO have fewer options. They do not have the APN, Network ID, or Type options.
Saving Your New (or Modified) Connection and Making Further Configurations
Once you have finished editing your mobile broadband connection, click the Apply button to save your customized configuration. If the profile was in use while being edited, power cycle the connection to make NetworkManager apply the changes. If the profile is OFF, set it to ON or select it in the network connection icon's menu. See Section 3.4.1, “Connecting to a Network Using the control-center GUI” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network Connections window and clicking Edit to return to the Editing dialog.
Then, to configure:

3.4.10. Configuring a DSL Connection with a GUI

This section is intended for those installations which have a DSL card fitted within a host rather than the external combined DSL modem router combinations typical of private consumer or SOHO installations.
3.4.10.1. Configuring a DSL Connection with nm-connection-editor
You can configure a DSL connection using the GNOME nm-connection-editor.
Adding a New DSL Connection
Procedure
  1. Enter nm-connection-editor in a terminal. The Network Connections window appears, see Section 3.4.3, “Common Configuration Options Using nm-connection-editor”.
  2. Click the plus button.
  3. The Choose a Connection Type list appears.
  4. Select DSL and press the Create button.
  5. The Editing DSL Connection 1 window appears.
Editing an Existing DSL Connection
Procedure
  1. Enter nm-connection-editor in a terminal. The Network Connections window appears.
  2. Select the connection you want to edit and click the gear wheel icon. See Section 3.4.3, “Common Configuration Options Using nm-connection-editor” for more information.
Configuring the DSL Tab
Username
Enter the user name used to authenticate with the service provider.
Service
Leave blank unless otherwise directed by your service provider.
Password
Enter the password supplied by the service provider.
Saving Your New (or Modified) Connection and Making Further Configurations
Once you have finished editing your DSL connection, click the Apply button to save your customized configuration. If the profile was in use while being edited, power cycle the connection to make NetworkManager apply the changes. If the profile is OFF, set it to ON or select it in the network connection icon's menu. See Section 3.4.1, “Connecting to a Network Using the control-center GUI” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network Connections window and clicking Edit to return to the Editing dialog.
To configure:

3.5. Configuring IP Networking with ifcfg Files

As a system administrator, you can configure a network interface manually, editing the ifcfg files.
Interface configuration (ifcfg) files control the software interfaces for individual network devices. As the system boots, it uses these files to determine what interfaces to bring up and how to configure them. These files are usually named ifcfg-name, where the suffix name refers to the name of the device that the configuration file controls. By convention, the ifcfg file's suffix is the same as the string given by the DEVICE directive in the configuration file itself.

Configuring an Interface with Static Network Settings Using ifcfg Files

For example, to configure an interface with static network settings using ifcfg files, for an interface with the name enp1s0, create a file with the name ifcfg-enp1s0 in the /etc/sysconfig/network-scripts/ directory, that contains:
  • For IPv4 configuration 
    DEVICE=enp1s0
BOOTPROTO=none
ONBOOT=yes
PREFIX=24
IPADDR=10.0.1.27
  • For IPv6 configuration 
    DEVICE=enp1s0
BOOTPROTO=none
ONBOOT=yes
IPV6INIT=yes
IPV6ADDR=2001:db8::2/48
    You do not need to specify the network or broadcast address as this is calculated automatically by ipcalc.
    For more IPv6 ifcfg configuration options, see nm-settings-ifcfg-rh(5) man page.

Important

In Red Hat Enterprise Linux 7, the naming convention for network interfaces has been changed, as explained in Chapter 11, Consistent Network Device Naming. Specifying the hardware or MAC address using HWADDR directive can influence the device naming procedure.

Configuring an Interface with Dynamic Network Settings Using ifcfg Files

To configure an interface named em1 with dynamic network settings using ifcfg files:
  1. Create a file with the name ifcfg-em1 in the /etc/sysconfig/network-scripts/ directory, that contains: 
    DEVICE=em1
BOOTPROTO=dhcp
ONBOOT=yes
  2. To configure an interface to send a different host name to the DHCP server, add the following line to the ifcfg file: 
    DHCP_HOSTNAME=hostname
    To configure an interface to send a different fully qualified domain name (FQDN) to the DHCP server, add the following line to the ifcfg file: 
    DHCP_FQDN=fully.qualified.domain.name

    Note

    Only one directive, either DHCP_HOSTNAME or DHCP_FQDN, should be used in a given ifcfg file. In case both DHCP_HOSTNAME and DHCP_FQDN are specified, only the latter is used.
  3. To configure an interface to use particular DNS servers, add the following lines to the ifcfg file: 
      PEERDNS=no
  DNS1=ip-address
  DNS2=ip-address
    where ip-address is the address of a DNS server. This will cause the network service to update /etc/resolv.conf with the specified DNS servers specified. Only one DNS server address is necessary, the other is optional.
  4. To configure static routes in the ifcfg file, see Section 4.5, “Configuring Static Routes in ifcfg files”.
    By default, NetworkManager calls the DHCP client, dhclient, when a profile has been set to obtain addresses automatically by setting BOOTPROTO to dhcp in an interface configuration file. If DHCP is required, an instance of dhclient is started for every Internet protocol, IPv4 and IPv6, on an interface. If NetworkManager is not running, or is not managing an interface, then the legacy network service will call instances of dhclient as required. For more details on dynamic IP addresses, see Section 1.2, “Comparing Static to Dynamic IP Addressing”.
  5. To apply the configuration:
    1. Reload the updated connection files: 
      # nmcli connection reload
    2. Re-activate the connection: 
      # nmcli connection up connection_name

3.5.1. Managing System-wide and Private Connection Profiles with ifcfg Files

The permissions correspond to the USERS directive in the ifcfg files. If the USERS directive is not present, the network profile will be available to all users. As an example, the following command in an ifcfg file will make the connection available only to the users listed: 
USERS="joe bob alice"
Also, you can set the USERCTL directive to manage the device:
  • If you set yes, non-root users are allowed to control this device.
  • If you set no, non-root users are not allowed to control this device.

3.6. Configuring IP Networking with ip Commands

As a system administrator, you can configure a network interface using the ip command, but but changes are not persistent across reboots; when you reboot, you will lose any changes.
The commands for the ip utility, sometimes referred to as iproute2 after the upstream package name, are documented in the man ip(8) page. The package name in Red Hat Enterprise Linux 7 is iproute. If necessary, you can check that the ip utility is installed by checking its version number as follows: 
~]$ ip -V
ip utility, iproute2-ss130716
The ip commands can be used to add and remove addresses and routes to interfaces in parallel with NetworkManager, which will preserve them and recognize them in nmcli, nmtui, control-center, and the D-Bus API.
To bring an interface down: 
ip link set ifname down

Note

The ip link set ifname command sets a network interface in IFF_UP state and enables it from the kernel's scope. This is different from the ifup ifname command for initscripts or NetworkManager's activation state of a device. In fact, NetworkManager always sets an interface up even if it is currently disconnected. Disconnecting the device through the nmcli tool, does not remove the IFF_UP flag. In this way, NetworkManager gets notifications about the carrier state.
Note that the ip utility replaces the ifconfig utility because the net-tools package (which provides ifconfig) does not support InfiniBand addresses.
For information about available OBJECTs, use the ip help command. For example: ip link help and ip addr help.

Note

ip commands given on the command line will not persist after a system restart. Where persistence is required, make use of configuration files (ifcfg files) or add the commands to a script.
Examples of using the command line and configuration files for each task are included after nmtui and nmcli examples but before explaining the use of one of the graphical user interfaces to NetworkManager, namely, control-center and nm-connection-editor.
The ip utility can be used to assign IP addresses to an interface with the following form: 
ip addr [ add | del ] address dev ifname

Assigning a Static Address Using ip Commands

To assign an IP address to an interface: 
~]# ip address add 10.0.0.3/24 dev enp1s0
You can view the address assignment of a specific device:
~]# ip addr show dev enp1s0
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether f0:de:f1:7b:6e:5f brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.3/24 brd 10.0.0.255 scope global global enp1s0
       valid_lft 58682sec preferred_lft 58682sec
    inet6 fe80::f2de:f1ff:fe7b:6e5f/64 scope link
       valid_lft forever preferred_lft forever
Further examples and command options can be found in the ip-address(8) manual page.

Configuring Multiple Addresses Using ip Commands

As the ip utility supports assigning multiple addresses to the same interface it is no longer necessary to use the alias interface method of binding multiple addresses to the same interface. The ip command to assign an address can be repeated multiple times in order to assign multiple address. For example: 
~]# ip address add 192.168.2.223/24 dev enp1s0
~]# ip address add 192.168.4.223/24 dev enp1s0
~]# ip addr
3: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 52:54:00:fb:77:9e brd ff:ff:ff:ff:ff:ff
    inet 192.168.2.223/24 scope global enp1s0
    inet 192.168.4.223/24 scope global enp1s0
For more details on the commands for the ip utility, see the ip(8) manual page.

Note

ip commands given on the command line will not persist after a system restart.

3.7. Configuring IP Networking from the Kernel Command line

When connecting to the root file system on an iSCSI target from an interface, the network settings are not configured on the installed system. For solution of this problem:
  1. Install the dracut utility. For information on using dracut, see Red Hat Enterprise Linux System Administrator's Guide
  2. Set the configuration using the ip option on the kernel command line: 
    ip<client-IP-number>:[<server-id>]:<gateway-IP-number>:<netmask>:<client-hostname>:<interface>:{dhcp|dhcp6|auto6|on|any|none|off}
    • dhcp - DHCP configuration
    • dhpc6 - DHCP IPv6 configuration
    • auto6 - automatic IPv6 configuration
    • on, any - any protocol available in the kernel (default)
    • none, off - no autoconfiguration, static network configuration
    For example: 
    ip=192.168.180.120:192.168.180.100:192.168.180.1:255.255.255.0::enp1s0:off
  3. Set the name server configuration: 
    nameserver=srv1 [nameserver=srv2 [nameserver=srv3 […]]]
The dracut utility sets up a network connection and generates new ifcfg files that can be copied to the /etc/sysconfig/network-scripts/ file.

3.8. Enabling IP Multicast with IGMP

The Internet Group Management Protocol (IGMP) enables the administrator to manage routing and subscription to multicast traffic between networks, hosts, and routers. The kernel in Red Hat Enterprise Linux supports IGMPv3.
To display multicast information, use the ip maddr show subcommand, for example: 
~]$ ip maddr show dev br0
8:	br0
	inet  224.0.0.1
	inet6 ff02::1
	inet6 ff01::1
[output truncated]
Alternatively, look for the MULTICAST string in the ip link show command output, for example: 
~]$ ip link show br0
8: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT qlen 1000
    link/ether 6c:0b:84:67:fe:63 brd ff:ff:ff:ff:ff:ff
To disable multicast on a device and to check that multicast is disabled on the br0 device: 
~]# ip link set multicast off dev br0
~]$ ip link show br0
8: br0: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT qlen 1000
    link/ether 6c:0b:84:67:fe:63 brd ff:ff:ff:ff:ff:ff
The missing MULTICAST string indicates that multicast is disabled.
To enable multicast on the br0 device and to check it is enabled: 
~]# ip link set multicast on dev br0
~]$ ip link show br0
8: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT qlen 1000
    link/ether 6c:0b:84:67:fe:63 brd ff:ff:ff:ff:ff:ff
See the ip Command Cheat Sheet for Red Hat Enterprise Linux article and the ip(8) man page for more information.
To check current version of IGMP and IP addresses subscribed for multicasting, see the /proc/net/igmp file: 
~]$ cat /proc/net/igmp

Note

IGMP is not enabled in firewalld by default. To enable IGMP for a zone: 
~]# firewall-cmd --zone=zone-name --add-protocol=igmp
See the Using Firewalls chapter in the Red Hat Enterprise Linux Security Guide for more information.

3.9. Additional Resources

Installed Documentation

  • ip(8) man page — Describes the ip utility's command syntax.
  • nmcli(1) man page — Describes NetworkManager's command‐line tool.
  • nmcli-examples(5) man page — Gives examples of nmcli commands.
  • nm-settings(5) man page — Describes NetworkManager properties and their settings.
  • nm-settings-ifcfg-rh(5) man page — Describes ifcfg-rh settings plug-in.

Online Documentation

Red Hat Enterprise Linux 7 Security Guide
Describes IPsec based VPN and its configuration. Describes the use of authenticated DNS queries using DNSSEC.
RFC 1518 — Classless Inter-Domain Routing (CIDR)
Describes the CIDR Address Assignment and Aggregation Strategy, including variable-length subnetting.
RFC 1918 — Address Allocation for Private Internets
Describes the range of IPv4 addresses reserved for private use.
RFC 3330 — Special-Use IPv4 Addresses
Describes the global and other specialized IPv4 address blocks that have been assigned by the Internet Assigned Numbers Authority (IANA).

Chapter 4. Configuring Static Routes and the Default Gateway

This chapter covers the configuration of static routes and the default gateway.

4.1. Introduction to Understanding Routing and Gateway

Routing is a mechanism that allows a system to find the network path to another system. Routing is often handled by devices on the network dedicated to routing (although any device can be configured to perform routing). Therefore, it is often not necessary to configure static routes on Red Hat Enterprise Linux servers or clients. Exceptions include traffic that must pass through an encrypted VPN tunnel or traffic that should take a specific route for reasons of cost or security. A host's routing table will be automatically populated with routes to directly connected networks. The routes examine when the network interfaces are “up”. In order to reach a remote network or host, the system is given the address of a gateway to which traffic should be sent.
When a host's interface is configured by DHCP, an address of a gateway that leads to an upstream network or the Internet is usually assigned. This gateway is usually referred to as the default gateway as it is the gateway to use if no better route is known to the system (and present in the routing table). Network administrators often use the first or last host IP address in the network as the gateway address; for example, 192.168.10.1 or 192.168.10.254. Not to be confused by the address which represents the network itself; in this example, 192.168.10.0, or the subnet's broadcast address; in this example 192.168.10.255. The default gateway is traditionally a network router. The default gateway is for any and all traffic which is not destined for the local network and for which no preferred route is specified in the routing table.

Note

To expand your expertise, you might also be interested in the Red Hat System Administration I (RH124) training course.

4.2. Configuring Static Routes Using nmcli

To configure static routes using the nmcli tool, use one of the following:
  • the nmcli command line
  • the nmcli interactive editor

Example 4.1. Configuring Static Routes Using nmcli

To configure a static route for an existing Ethernet connection using the command line: 
~]# nmcli connection modify enp1s0 +ipv4.routes "192.168.122.0/24 10.10.10.1"
This will direct traffic for the 192.168.122.0/24 subnet to the gateway at 10.10.10.1

Example 4.2. Configuring Static Routes with nmcli Editor

To configure a static route for an Ethernet connection using the interactive editor: 
~]$ nmcli con edit ens3
===| nmcli interactive connection editor |===

Editing existing '802-3-ethernet' connection: 'ens3'

Type 'help' or '?' for available commands.
Type 'describe [<setting>.<prop>]' for detailed property description.

You may edit the following settings: connection, 802-3-ethernet (ethernet), 802-1x, dcb, ipv4, ipv6, tc, proxy
nmcli> set ipv4.routes 192.168.122.0/24 10.10.10.1
nmcli> save persistent
Connection 'ens3' (23f8b65a-8f3d-41a0-a525-e3bc93be83b8) successfully updated.
nmcli> quit

4.3. Configuring Static Routes with GUI

To set a static route, open the IPv4 or IPv6 settings window for the connection you want to configure. See Section 3.4.1, “Connecting to a Network Using the control-center GUI” for instructions on how to do that.
Routes
Address — Enter the IP address of a remote network, sub-net, or host.
Netmask — The netmask or prefix length of the IP address entered above.
Gateway — The IP address of the gateway leading to the remote network, sub-net, or host entered above.
Metric — A network cost, a preference value to give to this route. Lower values will be preferred over higher values.
Automatic
When Automatic is ON, routes from RA or DHCP are used, but you can also add additional static routes. When OFF, only static routes you define are used.
Use this connection only for resources on its network
Select this check box to prevent the connection from becoming the default route. Typical examples are where a connection is a VPN tunnel or a leased line to a head office and you do not want any Internet-bound traffic to pass over the connection. Selecting this option means that only traffic specifically destined for routes learned automatically over the connection or entered here manually will be routed over the connection.

4.4. Configuring Static Routes with ip commands

As a system administrator, you can configure static routes using the ip route command.
To display the IP routing table, use the ip route command. For example: 
~]$ ip route
default via 192.168.122.1 dev ens9  proto static  metric 1024
192.168.122.0/24 dev ens9  proto kernel  scope link  src 192.168.122.107
192.168.122.0/24 dev enp1s0  proto kernel  scope link  src 192.168.122.126
The ip route commands take the following form: 
ip route [ add | del | change | append | replace ] destination-address
See the ip-route(8) man page for more details on the options and formats.
To add a static route to a host address, in other words to a single IP address: 
~]# ip route add 192.0.2.1 via 10.0.0.1 [dev interface]
where 192.0.2.1 is the IP address of the host in dotted decimal notation, 10.0.0.1 is the next hop address and interface is the exit interface leading to the next hop.
To add a static route to a network, in other words to an IP address representing a range of IP addresses: 
~]# ip route add 192.0.2.0/24 via 10.0.0.1 [dev interface]
where 192.0.2.0 is the IP address of the destination network in dotted decimal notation and /24 is the network prefix. The network prefix is the number of enabled bits in the subnet mask. This format of network address slash network prefix length is sometimes referred to as classless inter-domain routing (CIDR) notation.
To remove the assigned static route: 
~]# ip route del 192.0.2.1
Any changes that you make to the routing table using ip route do not persist across system reboots. To permanently configure static routes, you can configure them by creating a route-interface file in the /etc/sysconfig/network-scripts/ directory for the interface. For example, static routes for the enp1s0 interface would be stored in the /etc/sysconfig/network-scripts/route-enp1s0 file. Any changes that you make to a route-interface file do not take effect until you restart either the network service or the interface. The route-interface file has two formats:
See the ip-route(8) man page for more information on the ip route command.

4.5. Configuring Static Routes in ifcfg files

Static routes set using ip commands at the command prompt will be lost if the system is shutdown or restarted. To configure static routes to be persistent after a system restart, they must be placed in per-interface configuration files in the /etc/sysconfig/network-scripts/ directory. The file name should be of the format route-interface. There are two types of commands to use in the configuration files:

Static Routes Using the IP Command Arguments Format

If required in a per-interface configuration file, for example /etc/sysconfig/network-scripts/route-enp1s0, define a route to a default gateway on the first line. This is only required if the gateway is not set through DHCP and is not set globally in the /etc/sysconfig/network file: 
default via 192.168.1.1 dev interface
where 192.168.1.1 is the IP address of the default gateway. The interface is the interface that is connected to, or can reach, the default gateway. The dev option can be omitted, it is optional. Note that this setting takes precedence over a setting in the /etc/sysconfig/network file.
If a route to a remote network is required, a static route can be specified as follows. Each line is parsed as an individual route: 
10.10.10.0/24 via 192.168.1.1 [dev interface]
where 10.10.10.0/24 is the network address and prefix length of the remote or destination network. The address 192.168.1.1 is the IP address leading to the remote network. It is preferably the next hop address but the address of the exit interface will work. The “next hop” means the remote end of a link, for example a gateway or router. The dev option can be used to specify the exit interface interface but it is not required. Add as many static routes as required.
The following is an example of a route-interface file using the ip command arguments format. The default gateway is 192.168.0.1, interface enp1s0 and a leased line or WAN connection is available at 192.168.0.10. The two static routes are for reaching the 10.10.10.0/24 network and the 172.16.1.10/32 host: 
default via 192.168.0.1 dev enp1s0
10.10.10.0/24 via 192.168.0.10 dev enp1s0
172.16.1.10/32 via 192.168.0.10 dev enp1s0
In the above example, packets going to the local 192.168.0.0/24 network will be directed out the interface attached to that network. Packets going to the 10.10.10.0/24 network and 172.16.1.10/32 host will be directed to 192.168.0.10. Packets to unknown, remote, networks will use the default gateway therefore static routes should only be configured for remote networks or hosts if the default route is not suitable. Remote in this context means any networks or hosts that are not directly attached to the system.
For IPv6 configuration, an example of a route6-interface file in ip route format: 
2001:db8:1::/48 via 2001:db8::1 metric 2048
2001:db8:2::/48
Specifying an exit interface is optional. It can be useful if you want to force traffic out of a specific interface. For example, in the case of a VPN, you can force traffic to a remote network to pass through a tun0 interface even when the interface is in a different subnet to the destination network.
The ip route format can be used to specify a source address. For example: 
10.10.10.0/24 via 192.168.0.10 src 192.168.0.2
To define an existing policy-based routing configuration, which specifies multiple routing tables, see Section 4.5.1, “Understanding Policy-routing”.

Important

If the default gateway is already assigned by DHCP and if the same gateway with the same metric is specified in a configuration file, an error during start-up, or when bringing up an interface, will occur. The follow error message may be shown: "RTNETLINK answers: File exists". This error may be ignored.

Static Routes Using the Network/Netmask Directives Format

You can also use the network/netmask directives format for route-interface files. The following is a template for the network/netmask format, with instructions following afterwards: 
ADDRESS0=10.10.10.0
NETMASK0=255.255.255.0
GATEWAY0=192.168.1.1
  • ADDRESS0=10.10.10.0 is the network address of the remote network or host to be reached.
  • NETMASK0=255.255.255.0 is the netmask for the network address defined with ADDRESS0=10.10.10.0.
  • GATEWAY0=192.168.1.1 is the default gateway, or an IP address that can be used to reach ADDRESS0=10.10.10.0
The following is an example of a route-interface file using the network/netmask directives format. The default gateway is 192.168.0.1 but a leased line or WAN connection is available at 192.168.0.10. The two static routes are for reaching the 10.10.10.0/24 and 172.16.1.0/24 networks: 
ADDRESS0=10.10.10.0
NETMASK0=255.255.255.0
GATEWAY0=192.168.0.10
ADDRESS1=172.16.1.10
NETMASK1=255.255.255.0
GATEWAY1=192.168.0.10
Subsequent static routes must be numbered sequentially, and must not skip any values. For example, ADDRESS0, ADDRESS1, ADDRESS2, and so on.
By default, forwarding packets from one interface to another, or out of the same interface, is disabled for security reasons. This prevents the system acting as a router for external traffic. If you need the system to route external traffic, such as when sharing a connection or configuring a VPN server, you will need to enable IP forwarding. See the Red Hat Enterprise Linux 7 Security Guide for more details.

4.5.1. Understanding Policy-routing

Policy-routing also known as source-routing, is a mechanism for more flexible routing configurations. Routing decisions are commonly made based on the destination IP address of a package. Policy-routing allows more flexibility to select routes based on other routing properties, such as source IP address, source port, protocol type. Routing tables stores route information about networks. They are identified by either numeric values or names, which can be configured in the /etc/iproute2/rt_tables file. The default table is identified with 254. Using policy-routing, you also need rules. Rules are used to select a routing table, based on certain properties of packets.
For initscripts, the routing table is a property of the route that can be configured through the table argument. The ip route format can be used to define an existing policy-based routing configuration, which specifies multiple routing tables: 
10.10.10.0/24 via 192.168.0.10 table 1
10.10.10.0/24 via 192.168.0.10 table 2
To specify routing rules in initscripts, edit them to the /etc/sysconfig/network-scripts/rule-enp1s0 file for IPv4 or to the /etc/sysconfig/network-scripts/rule6-enp1s0 file for IPv6.
NetworkManager supports policy-routing, but rules are not supported yet. The rules must be configured by the user running a custom script. For each manual static route, a routing table can be selected:
  • ipv4.route-table for IPv4
    and
  • ipv6.route-table for IPv6.
By setting routes to a particular table, all routes from DHCP, autoconf6, DHCP6 are placed in that specific table. In addition, all routes for subnets that have already configured addresses, are placed in the corresponding routing table. For example, if you configure the 192.168.1.10/24 address, the 192.168.1.0/24 subnet is contained in ipv4.route-table.
For more details about policy-routing rules, see the ip-rule(8) man page. For routing tables, see the ip-route(8) man page.

4.6. Configuring the Default Gateway

The default gateway is determined by the network scripts which parse the /etc/sysconfig/network file first and then the network interface ifcfg files for interfaces that are “up”. The ifcfg files are parsed in numerically ascending order, and the last GATEWAY directive to be read is used to compose a default route in the routing table.
You can specify the default route using the GATEWAY directive, either globally or in interface-specific configuration files. However, in Red Hat Enterprise Linux the use of the global /etc/sysconfig/network file is deprecated, and specifying the gateway should now only be done in per-interface configuration files.
In dynamic network environments, where mobile hosts are managed by NetworkManager, gateway information is likely to be interface specific and is best left to be assigned by DHCP. In special cases where it is necessary to influence NetworkManager's selection of the exit interface to be used to reach a gateway, make use of the DEFROUTE=no command in the ifcfg files for those interfaces which do not lead to the default gateway.

Chapter 5. Configuring Network Connection Settings

This chapter describes various configurations of the network connection settings and shows how to configure them by using NetworkManager.

5.2. Configuring 802.1X Security

802.1X security is the name of the IEEE standard for port-based Network Access Control (PNAC). It is also called WPA Enterprise. 802.1X security is a way of controlling access to a logical network from a physical one. All clients who want to join the logical network must authenticate with the server (a router, for example) using the correct 802.1X authentication method.
802.1X security is most often associated with securing wireless networks (WLANs), but can also be used to prevent intruders with physical access to the network (LAN) from gaining entry.
In the past, DHCP servers were configured not to lease IP addresses to unauthorized users, but for various reasons this practice is both impractical and insecure, and thus is no longer recommended. Instead, 802.1X security is used to ensure a logically-secure network through port-based authentication.
802.1X provides a framework for WLAN and LAN access control and serves as an envelope for carrying one of the Extensible Authentication Protocol (EAP) types. An EAP type is a protocol that defines how security is achieved on the network.

5.2.1. Configuring 802.1X Security for Wi-Fi with nmcli

Procedure
  1. Set the authenticated key-mgmt (key management) protocol. It configures the keying mechanism for a secure wifi connection. See the nm-settings(5) man page for more details on properties.
  2. Configure the 802-1x authentication settings. For the Transport Layer Security (TLS) authentication, see the section called “Configuring TLS Settings”.
Table 5.1. The 802-1x authentication settings
802-1x authentication setting Name  
802-1x.identity Identity  
802-1x.ca-cert CA certificate  
802-1x.client-cert User certificate  
802-1x.private-key Private key  
802-1x.private-key-password Private key password  
For example, to configure WPA2 Enterprise using the EAP-TLS authentication method, apply the following settings: 
nmcli c add type wifi ifname wlo61s0 con-name 'My Wifi Network' \
      802-11-wireless.ssid 'My Wifi' \
      802-11-wireless-security.key-mgmt wpa-eap \
      802-1x.eap tls \
      802-1x.identity identity@example.com \
      802-1x.ca-cert /etc/pki/my-wifi/ca.crt \
      802-1x.client-cert /etc/pki/my-wifi/client.crt \
      802-1x.private-key /etc/pki/my-wifi/client.key \
      802-1x.private-key-password s3cr3t

5.2.2. Configuring 802.1X Security for Wired with nmcli

To configure a wired connection using the nmcli tool, follow the same procedure as for a wireless connection, except the 802-11-wireless.ssid and 802-11-wireless-security.key-mgmt settings.

5.2.3. Configuring 802.1X Security for Wi-Fi with a GUI

Procedure
  1. Open the Network window (see Section 3.4.1, “Connecting to a Network Using the control-center GUI”).
  2. Select a Wireless network interface from the right-hand-side menu. If necessary, set the symbolic power button to ON and check that your hardware switch is on.
  3. Either select the connection name of a new connection, or click the gear wheel icon of an existing connection profile, for which you want to configure 802.1X security. In the case of a new connection, complete any authentication steps to complete the connection and then click the gear wheel icon.
  4. Select Security.
    The following configuration options are available:
    Security
    None — Do not encrypt the Wi-Fi connection.
    WEP 40/128-bit Key — Wired Equivalent Privacy (WEP), from the IEEE 802.11 standard. Uses a single pre-shared key (PSK).
    WEP 128-bit Passphrase — An MD5 hash of the passphrase will be used to derive a WEP key.
    LEAP — Lightweight Extensible Authentication Protocol, from Cisco Systems.
    Dynamic WEP (802.1X) — WEP keys are changed dynamically. Use with the section called “Configuring TLS Settings”
    WPA & WPA2 Personal — Wi-Fi Protected Access (WPA), from the draft IEEE 802.11i standard. A replacement for WEP. Wi-Fi Protected Access II (WPA2), from the 802.11i-2004 standard. Personal mode uses a pre-shared key (WPA-PSK).
    WPA & WPA2 Enterprise — WPA for use with a RADIUS authentication server to provide IEEE 802.1X network access control. Use with the section called “Configuring TLS Settings”
    Password
    Enter the password to be used in the authentication process.
  5. From the drop-down menu select one of the following security methods: LEAP, Dynamic WEP (802.1X), or WPA & WPA2 Enterprise.
See the section called “Configuring TLS Settings” for descriptions of which extensible authentication protocol (EAP) types correspond to your selection in the Security drop-down menu.

5.2.4. Configuring 802.1X Security for Wired with nm-connection-editor

Procedure
  1. Enter the nm-connection-editor in a terminal. 
    ~]$ nm-connection-editor
    The Network Connections window appears.
  2. Select the ethernet connection you want to edit and click the gear wheel icon, see Section 3.4.6.2, “Configuring a Wired Connection with nm-connection-editor”.
  3. Select Security and set the symbolic power button to ON to enable settings configuration.
  4. Select from one of following authentication methods:
Configuring TLS Settings
With Transport Layer Security (TLS), the client and server mutually authenticate using the TLS protocol. The server demonstrates that it holds a digital certificate, the client proves its own identity using its client-side certificate, and key information is exchanged. Once authentication is complete, the TLS tunnel is no longer used. Instead, the client and server use the exchanged keys to encrypt data using AES, TKIP or WEP.
The fact that certificates must be distributed to all clients who want to authenticate means that the EAP-TLS authentication method is very strong, but also more complicated to set up. Using TLS security requires the overhead of a public key infrastructure (PKI) to manage certificates. The benefit of using TLS security is that a compromised password does not allow access to the (W)LAN: an intruder must also have access to the authenticating client's private key.
NetworkManager does not determine the version of TLS supported. NetworkManager gathers the parameters entered by the user and passes them to the daemon, wpa_supplicant, that handles the procedure. It in turn uses OpenSSL to establish the TLS tunnel. OpenSSL itself negotiates the SSL/TLS protocol version. It uses the highest version both ends support.
To configure TLS settings, follow the procedure described in Section 5.2.4, “Configuring 802.1X Security for Wired with nm-connection-editor”. The following configuration settings are available:
Identity
Provide the identity of this server.
User certificate
Click to browse for, and select, a personal X.509 certificate file encoded with Distinguished Encoding Rules (DER) or Privacy Enhanced Mail (PEM).
CA certificate
Click to browse for, and select, an X.509 certificate authority certificate file encoded with Distinguished Encoding Rules (DER) or Privacy Enhanced Mail (PEM).
Private key
Click to browse for, and select, a private key file encoded with Distinguished Encoding Rules (DER), Privacy Enhanced Mail (PEM), or the Personal Information Exchange Syntax Standard (PKCS #12).
Private key password
Enter the password for the private key in the Private key field. Select Show password to make the password visible as you type it.
Configuring FAST Settings
To configure FAST settings, follow the procedure described in Section 5.2.4, “Configuring 802.1X Security for Wired with nm-connection-editor”. The following configuration settings are available:
Anonymous Identity
Provide the identity of this server.
PAC provisioning
Select the check box to enable and then select from Anonymous, Authenticated, and Both.
PAC file
Click to browse for, and select, a protected access credential (PAC) file.
Inner authentication
GTC — Generic Token Card.
MSCHAPv2 — Microsoft Challenge Handshake Authentication Protocol version 2.
Username
Enter the user name to be used in the authentication process.
Password
Enter the password to be used in the authentication process.
Configuring Tunneled TLS Settings
To configure Tunneled TLS settings, follow the procedure described in Section 5.2.4, “Configuring 802.1X Security for Wired with nm-connection-editor”. The following configuration settings are available:
Anonymous identity
This value is used as the unencrypted identity.
CA certificate
Click to browse for, and select, a Certificate Authority's certificate.
Inner authentication
PAP — Password Authentication Protocol.
MSCHAP — Challenge Handshake Authentication Protocol.
MSCHAPv2 — Microsoft Challenge Handshake Authentication Protocol version 2.
CHAP — Challenge Handshake Authentication Protocol.
Username
Enter the user name to be used in the authentication process.
Password
Enter the password to be used in the authentication process.
Configuring Protected EAP (PEAP) Settings
To configure Protected EAP (PEAP) settings, follow the procedure described in Section 5.2.4, “Configuring 802.1X Security for Wired with nm-connection-editor”. The following configuration settings are available:
Anonymous Identity
This value is used as the unencrypted identity.
CA certificate
Click to browse for, and select, a Certificate Authority's certificate.
PEAP version
The version of Protected EAP to use. Automatic, 0 or 1.
Inner authentication
MSCHAPv2 — Microsoft Challenge Handshake Authentication Protocol version 2.
MD5 — Message Digest 5, a cryptographic hash function.
GTC — Generic Token Card.
Username
Enter the user name to be used in the authentication process.
Password
Enter the password to be used in the authentication process.

5.3. Using MACsec with wpa_supplicant and NetworkManager

Media Access Control Security (MACsec, IEEE 802.1AE) encrypts and authenticates all traffic in LANs with the GCM-AES-128 algorithm. MACsec can protect not only IP but also Address Resolution Protocol (ARP), Neighbor Discovery (ND), or DHCP. While IPsec operates on the network layer (layer 3) and SSL or TLS on the application layer (layer 7), MACsec operates in the data link layer (layer 2). Combine MACsec with security protocols for other networking layers to take advantage of different security features that these standards provide.
To enable MACsec with a switch that performs authentication using a pre-shared Connectivity Association Key/CAK Name (CAK/CKN) pair:
Procedure
  1. Create a CAK/CKN pair. For example, the following command generates a 16-byte key in hexadecimal notation: 
    ~]$ dd if=/dev/urandom count=16 bs=1 2> /dev/null | hexdump -e '1/2 "%02x"'
  2. Create the wpa_supplicant.conf configuration file and add the following lines to it: 
    ctrl_interface=/var/run/wpa_supplicant
eapol_version=3
ap_scan=0
fast_reauth=1

network={
    key_mgmt=NONE
    eapol_flags=0
    macsec_policy=1

    mka_cak=0011... # 16 bytes hexadecimal
    mka_ckn=2233... # 32 bytes hexadecimal
}
    Use the values from the previous step to complete the mka_cak and mka_ckn lines in the wpa_supplicant.conf configuration file.
    See the wpa_supplicant.conf(5) man page for more information.
  3. Assuming you are using wlp61s0 to connect to your network, start wpa_supplicant using the following command: 
    ~]# wpa_supplicant -i wlp61s0 -Dmacsec_linux -c wpa_supplicant.conf
Instead of creating and editing the wpa_supplicant.conf file, Red Hat recommends using the nmcli command to configure wpa_supplicant equivalently as in the previous steps. The following example assumes that you already have a 16-byte hexadecimal CAK ($MKA_CAK) and a 32-byte hexadecimal CKN ($MKA_CKN): 
~]# nmcli connection add type macsec \
  con-name test-macsec+ ifname macsec0 \
  connection.autoconnect no \
  macsec.parent wlp61s0 macsec.mode psk \
  macsec.mka-cak $MKA_CAK \
  macsec.mka-cak-flags 0 \
  macsec.mka-ckn $MKA_CKN

~]# nmcli connection up test-macsec+
After this step, the macsec0 device should be configured and used for networking.
For more details, see the What’s new in MACsec: setting up MACsec using wpa_supplicant and (optionally) NetworkManager article. In addition, see the MACsec: a different solution to encrypt network traffic article for more information about the architecture of a MACsec network, use case scenarios, and configuration examples.

5.4. Configuring IPv4 Settings

Configuring IPv4 Settings with control-center

Procedure
  1. Press the Super key to enter the Activities Overview, type Settings and then press Enter. Then, select the Network tab on the left-hand side, and the Network settings tool appears. Proceed to the section called “Configuring New Connections with control-center”.
  2. Select the connection that you want to edit and click on the gear wheel icon. The Editing dialog appears.
  3. Click the IPv4 menu entry.
The IPv4 menu entry allows you to configure the method used to connect to a network, to enter IP address,DNS and route information as required. The IPv4 menu entry is available when you create and modify one of the following connection types: wired, wireless, mobile broadband, VPN or DSL.
If you are using DHCP to obtain a dynamic IP address from a DHCP server, you can simply set Addresses to Automatic (DHCP).
If you need to configure static routes, see Section 4.3, “Configuring Static Routes with GUI”.

Setting the Method for IPV4 Using nm-connection-editor

You can use the nm-connection-editor to edit and configure connection settings. This procedure describes how you can configure the IPv4 settings:
Procedure
  1. Enter nm-connection-editor in a terminal.
  2. For an existing connection type, click the gear wheel icon.
    Editing a connection

    Figure 5.2. Editing a connection

  3. Click IPv4 Settings.
    Configuring IPv4 Settings

    Figure 5.3. Configuring IPv4 Settings

Available IPv4 Methods by Connection Type

When you click the Method drop-down menu, depending on the type of connection you are configuring, you are able to select one of the following IPv4 connection methods. All of the methods are listed here according to which connection type, or types, they are associated with:
Wired, Wireless and DSL Connection Methods
Automatic (DHCP) — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses. You do not need to fill in the DHCP client ID field.
Automatic (DHCP) addresses only — Choose this option if the network you are connecting to uses a DHCP server to assign IP addresses but you want to assign DNS servers manually.
Manual — Choose this option if you want to assign IP addresses manually.
Link-Local Only — Choose this option if the network you are connecting to does not have a DHCP server and you do not want to assign IP addresses manually. Random addresses will be assigned as per RFC 3927 with prefix 169.254/16.
Shared to other computers — Choose this option if the interface you are configuring is for sharing an Internet or WAN connection. The interface is assigned an address in the 10.42.x.1/24 range, a DHCP server and DNS server are started, and the interface is connected to the default network connection on the system with network address translation (NAT).
Disabled — IPv4 is disabled for this connection.
Mobile Broadband Connection Methods
Automatic (PPP) — Choose this option if the network you are connecting to assigns your IP address and DNS servers automatically.
Automatic (PPP) addresses only — Choose this option if the network you are connecting to assigns your IP address automatically, but you want to manually specify DNS servers.
VPN Connection Methods
Automatic (VPN) — Choose this option if the network you are connecting to assigns your IP address and DNS servers automatically.
Automatic (VPN) addresses only — Choose this option if the network you are connecting to assigns your IP address automatically, but you want to manually specify DNS servers.
DSL Connection Methods
Automatic (PPPoE) — Choose this option if the network you are connecting to assigns your IP address and DNS servers automatically.
Automatic (PPPoE) addresses only — Choose this option if the network you are connecting to assigns your IP address automatically, but you want to manually specify DNS servers.
If you are using DHCP to obtain a dynamic IP address from a DHCP server, you can simply set Method to Automatic (DHCP).
If you need to configure static routes, click the Routes button and for more details on configuration options, see Section 4.3, “Configuring Static Routes with GUI”.

5.5. Configuring IPv6 Settings

To configure IPv6 settings, follow the procedure described in Section 5.4, “Configuring IPv4 Settings” and click the IPv6 menu entry.
Method
Ignore — Choose this option if you want to ignore IPv6 settings for this connection.
Automatic — Choose this option to use SLAAC to create an automatic, stateless configuration based on the hardware address and router advertisements (RA).
Automatic, addresses only — Choose this option if the network you are connecting to uses router advertisements (RA) to create an automatic, stateless configuration, but you want to assign DNS servers manually.
Automatic, DHCP only — Choose this option to not use RA, but request information from DHCPv6 directly to create a stateful configuration.
Manual — Choose this option if you want to assign IP addresses manually.
Link-Local Only — Choose this option if the network you are connecting to does not have a DHCP server and you do not want to assign IP addresses manually. Random addresses will be assigned as per RFC 4862 with prefix FE80::0.
Addresses
DNS servers — Enter a comma separated list of DNS servers.
Search domains — Enter a comma separated list of domain controllers.
If you need to configure static routes, click the Routes button and for more details on configuration options, see Section 4.3, “Configuring Static Routes with GUI”.

5.6. Configuring PPP (Point-to-Point) Settings

Authentication Methods
In most cases, the provider’s PPP servers supports all the allowed authentication methods. If a connection fails, the user should disable support for some methods, depending on the PPP server configuration.
Use point-to-point encryption (MPPE)
Microsoft Point-To-Point Encryption protocol (RFC 3078).
Allow BSD data compression
PPP BSD Compression Protocol (RFC 1977).
Allow Deflate data compression
PPP Deflate Protocol (RFC 1979).
Use TCP header compression
Compressing TCP/IP Headers for Low-Speed Serial Links (RFC 1144).
Send PPP echo packets
LCP Echo-Request and Echo-Reply Codes for loopback tests (RFC 1661).

Note

Since the PPP support in NetworkManager is optional, to configure PPP settings, make sure that the NetworkManager-ppp package is already installed.

Chapter 6. Configure Host Names

6.1. Understanding Host Names

There are three classes of hostname: static, pretty, and transient.
The “static” host name is the traditional hostname, which can be chosen by the user, and is stored in the /etc/hostname file. The “transient” hostname is a dynamic host name maintained by the kernel. It is initialized to the static host name by default, whose value defaults to “localhost”. It can be changed by DHCP or mDNS at runtime. The “pretty” hostname is a free-form UTF8 host name for presentation to the user.

Note

A host name can be a free-form string up to 64 characters in length. However, Red Hat recommends that both static and transient names match the fully-qualified domain name (FQDN) used for the machine in DNS, such as host.example.com. It is also recommended that the static and transient names consists only of 7 bit ASCII lower-case characters, no spaces or dots, and limits itself to the format allowed for DNS domain name labels, even though this is not a strict requirement. Older specifications do not permit the underscore, and so their use is not recommended.
The hostnamectl tool will enforce the following: Static and transient host names to consist of a-z, A-Z, 0-9, “-”, “_” and “.” only, to not begin or end in a dot, and to not have two dots immediately following each other. The size limit of 64 characters is enforced.

6.2. Configuring Host Names Using Text User Interface, nmtui

The text user interface tool nmtui can be used to configure a host name in a terminal window. Issue the following command to start the tool: 
~]$ nmtui
The text user interface appears. Any invalid command prints a usage message.
The NetworkManager Text User Interface starting menu

Figure 6.1. The NetworkManager Text User Interface starting menu

To navigate, use the arrow keys or press Tab to step forwards and press Shift+Tab to step back through the options. Press Enter to select an option. The Space bar toggles the status of a check box.
See Section 3.2, “Configuring IP Networking with nmtui” for information on installing nmtui.
The NetworkManager text user interface tool nmtui can be used to query and set the static host name in the /etc/hostname file.

Important

In Red Hat Enterprise Linux, NetworkManager uses the systemd-hostnamed service to read and write the static host name, which is stored in the /etc/hostname file. Due to this, manual modifications done to the /etc/hostname file are no longer picked up automatically by NetworkManager; you should change the system host name through the hostnamectl utility. Also, the use of the HOSTNAME variable in the /etc/sysconfig/network file is now deprecated.

6.3. Configuring Host Names Using hostnamectl

The hostnamectl tool is provided for administering the three separate classes of host names in use on a given system.

6.3.1. View All the Host Names

To view all the current host names, enter the following command: 
~]$ hostnamectl status
The status option is implied by default if no option is given.

6.3.2. Set All the Host Names

To set all the host names on a system, enter the following command as root: 
~]# hostnamectl set-hostname name
This will alter the pretty, static, and transient host names alike. The static and transient host names will be simplified forms of the pretty host name. Spaces will be replaced with “-” and special characters will be removed.

6.3.3. Set a Particular Host Name

To set a particular host name, enter the following command as root with the relevant option: 
~]# hostnamectl set-hostname name [option...]
Where option is one or more of: --pretty, --static, and --transient.
If the --static or --transient options are used together with the --pretty option, the static and transient host names will be simplified forms of the pretty host name. Spaces will be replaced with “-” and special characters will be removed. If the --pretty option is not given, no simplification takes place.
When setting a pretty host name, remember to use the appropriate quotation marks if the host name contains spaces or a single quotation mark. For example: 
~]# hostnamectl set-hostname "Stephen's notebook" --pretty

6.3.4. Clear a Particular Host Name

To clear a particular host name and allow it to revert to the default, enter the following command as root with the relevant option: 
~]# hostnamectl set-hostname "" [option...]
Where "" is a quoted empty string and where option is one or more of: --pretty, --static, and --transient.

6.3.5. Changing Host Names Remotely

To execute a hostnamectl command on a remote system, use the -H, --host option as follows: 
~]# hostnamectl set-hostname -H [username]@hostname
Where hostname is the remote host you want to configure. The username is optional. The hostnamectl tool will use SSH to connect to the remote system.

6.4. Configuring Host Names Using nmcli

The NetworkManager tool nmcli can be used to query and set the static host name in the /etc/hostname file.
To query the static host name, issue the following command: 
~]$ nmcli general hostname
To set the static host name to my-server, issue the following command as root: 
~]# nmcli general hostname my-server

6.5. Additional Resources

  • hostnamectl(1) man page — Describes hostnamectl including the commands and command options.
  • hostname(1) man page — Contains an explanation of the hostname and domainname commands.
  • hostname(5) man page — Contains an explanation of the host name file, its contents, and use.
  • hostname(7) man page — Contains an explanation of host name resolution.
  • machine-info(5) man page — Describes the local machine information file and the environment variables it contains.
  • machine-id(5) man page — Describes the local machine ID configuration file.
  • systemd-hostnamed.service(8) man page — Describes the systemd-hostnamed system service used by hostnamectl.

Chapter 7. Configure Network Bonding

Red Hat Enterprise Linux 7 allows administrators to bind multiple network interfaces together into a single, bonded, channel. Channel bonding enables two or more network interfaces to act as one, simultaneously increasing the bandwidth and providing redundancy.

Warning

The use of direct cable connections without network switches is not supported for bonding. The failover mechanisms described here will not work as expected without the presence of network switches. See the Red Hat Knowledgebase article Why is bonding in not supported with direct connection using crossover cables? for more information.

Note

The active-backup, balance-tlb and balance-alb modes do not require any specific configuration of the switch. Other bonding modes require configuring the switch to aggregate the links. For example, a Cisco switch requires EtherChannel for Modes 0, 2, and 3, but for Mode 4 LACP and EtherChannel are required. See the documentation supplied with your switch and see https://www.kernel.org/doc/Documentation/networking/bonding.txt

7.1. Understanding the Default Behavior of Controller and Port Interfaces

When controlling bonded port interfaces using the NetworkManager daemon, and especially when fault finding, keep the following in mind:
  1. Starting the controller interface does not automatically start the port interfaces.
  2. Starting a port interface always starts the controller interface.
  3. Stopping the controller interface also stops the port interfaces.
  4. A controller without ports can start static IP connections.
  5. A controller without ports waits for ports when starting DHCP connections.
  6. A controller with a DHCP connection waiting for ports completes when a port with a carrier is added.
  7. A controller with a DHCP connection waiting for ports continues waiting when a port without a carrier is added.

7.2. Configure Bonding Using the Text User Interface, nmtui

The text user interface tool nmtui can be used to configure bonding in a terminal window. Issue the following command to start the tool: 
~]$ nmtui
The text user interface appears. Any invalid command prints a usage message.
To navigate, use the arrow keys or press Tab to step forwards and press Shift+Tab to step back through the options. Press Enter to select an option. The Space bar toggles the status of a check box.
  1. From the starting menu, select Edit a connection. Select Add, the New Connection screen opens.
    The NetworkManager Text User Interface Add a Bond Connection menu

    Figure 7.1. The NetworkManager Text User Interface Add a Bond Connection menu

  2. Select Bond and then Create; the Edit connection screen for the bond will open.
    The NetworkManager Text User Interface Configuring a Bond Connection menu

    Figure 7.2. The NetworkManager Text User Interface Configuring a Bond Connection menu

  3. At this point port interfaces will need to be added to the bond; to add these select Add, the New Connection screen opens. Once the type of Connection has been chosen select the Create button.
    The NetworkManager Text User Interface Configuring a New Bond Slave Connection menu

    Figure 7.3. The NetworkManager Text User Interface Configuring a New Bond Slave Connection menu

  4. The port's Edit Connection display appears; enter the required port's device name or MAC address in the Device section. If required, enter a clone MAC address to be used as the bond's MAC address by selecting Show to the right of the Ethernet label. Select the OK button to save the port.

    Note

    If the device is specified without a MAC address the Device section will be automatically populated once the Edit Connection window is reloaded, but only if it successfully finds the device.
    The NetworkManager Text User Interface Configuring a Bond Slave Connection menu

    Figure 7.4. The NetworkManager Text User Interface Configuring a Bond Slave Connection menu

  5. The name of the bond port appears in the Slaves section. Repeat the above steps to add further port connections.
  6. Review and confirm the settings before selecting the OK button.
    The NetworkManager Text User Interface Completed Bond

    Figure 7.5. The NetworkManager Text User Interface Completed Bond

See Section 7.8.1.1, “Configuring the Bond Tab” for definitions of the bond terms.
See Section 3.2, “Configuring IP Networking with nmtui” for information on installing nmtui.

7.3. Network Bonding Using the NetworkManager Command Line Tool, nmcli

Note

See Section 3.3, “Configuring IP Networking with nmcli” for an introduction to nmcli.
To create a bond connection with the nmcli tool, issue the following command: 
~]$ nmcli con add type bond ifname mybond0
Connection 'bond-mybond0' (5f739690-47e8-444b-9620-1895316a28ba) successfully added.
Note that as no con-name was given for the bond, the connection name was derived from the interface name by prepending the type.
NetworkManager supports most of the bonding options provided by the kernel. For example: 
~]$ nmcli con add type bond ifname mybond0 bond.options "mode=balance-rr,miimon=100"
Connection 'bond-mybond0' (5f739690-47e8-444b-9620-1895316a28ba) successfully added.
To add a port interface:
  1. Create a new connection, see Section 3.3.5, “Creating and Modifying a Connection Profile with nmcli” for details.
  2. Set the controller property to the bond interface name, or to the name of the controller connection: 
~]$ nmcli con add type ethernet ifname ens3 master mybond0
Connection 'bond-slave-ens3' (220f99c6-ee0a-42a1-820e-454cbabc2618) successfully added.
To add a new port interface, repeat the previous command with the new interface. For example: 
~]$ nmcli con add type ethernet ifname ens7 master mybond0
Connection 'bond-slave-ens7' (ecc24c75-1c89-401f-90c8-9706531e0231) successfully added.
To activate the ports, issue a command as follows: 
~]$ nmcli con up bond-slave-ens7
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/14)
~]$ nmcli con up bond-slave-ens3
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/15)
When you activate a port, the controller connection also starts. You can see Section 7.1, “Understanding the Default Behavior of Controller and Port Interfaces” for more information. In this case, it is not necessary to manually activate the controller connection.
It is possible to change the active_slave option and the primary option of the bond at runtime, without deactivating the connection. For example to change the active_slave option, issue the following command: 
~]$ nmcli dev mod bond0 +bond.options "active_slave=ens7"
Connection successfully reapplied to device 'bond0'.
or to change the primary option: 
~]$ nmcli dev mod bond0 +bond.options "primary=ens3"
Connection successfully reapplied to device 'bond0'.

Note

The active_slave option sets the currently active port whereas the primary option of the bond specifies the active port to be automatically selected by kernel when a new port is added or a failure of the active port occurs.

7.4. Using the Command Line Interface (CLI)

A bond is created using the bonding kernel module and a special network interface called a channel bonding interface.

7.4.1. Check if Bonding Kernel Module is Installed

In Red Hat Enterprise Linux 7, the bonding module is not loaded by default. You can load the module by issuing the following command as root: 
~]# modprobe --first-time bonding
This activation will not persist across system restarts. See the Red Hat Enterprise Linux Kernel Administration Guide for an explanation of persistent module loading. Note that given a correct configuration file using the BONDING_OPTS directive, the bonding module will be loaded as required and therefore does not need to be loaded separately.
To display information about the module, issue the following command: 
~]$ modinfo bonding
See the modprobe(8) man page for more command options.

7.4.2. Create a Channel Bonding Interface

To create a channel bonding interface, create a file in the /etc/sysconfig/network-scripts/ directory called ifcfg-bondN, replacing N with the number for the interface, such as 0.
The contents of the file can be based on a configuration file for whatever type of interface is getting bonded, such as an Ethernet interface. The essential differences are that the DEVICE directive is bondN, replacing N with the number for the interface, and TYPE=Bond. In addition, set BONDING_MASTER=yes.

Example 7.1. Example ifcfg-bond0 Interface Configuration File

An example of a channel bonding interface. 
DEVICE=bond0
NAME=bond0
TYPE=Bond
BONDING_MASTER=yes
IPADDR=192.168.1.1
PREFIX=24
ONBOOT=yes
BOOTPROTO=none
BONDING_OPTS="bonding parameters separated by spaces"
NM_CONTROLLED="no"
The NAME directive is useful for naming the connection profile in NetworkManager. ONBOOT says whether the profile should be started when booting (or more generally, when auto-connecting a device).

Important

Parameters for the bonding kernel module must be specified as a space-separated list in the BONDING_OPTS="bonding parameters" directive in the ifcfg-bondN interface file. Do not specify options for the bonding device in /etc/modprobe.d/bonding.conf, or in the deprecated /etc/modprobe.conf file.
The max_bonds parameter is not interface specific and should not be set when using ifcfg-bondN files with the BONDING_OPTS directive as this directive will cause the network scripts to create the bond interfaces as required.
For further instructions and advice on configuring the bonding module and to view the list of bonding parameters, see Section 7.7, “Using Channel Bonding”.
Note that if the NM_CONTROLLED="no" setting is not present, NetworkManager might override settings in this configuration file.

7.4.3. Creating Port Interfaces

The channel bonding interface is the controller (also refered to as master) and the interfaces to be bonded are referred to as the ports (slaves). After the channel bonding interface is created, the network interfaces to be bound together must be configured by adding the MASTER and SLAVE directives to the configuration files of the ports. The configuration files for each of the port interfaces can be nearly identical.

Example 7.2. Example Port Interface Configuration File

For example, if two Ethernet interfaces are being channel bonded, enp1s0 and enp2s0, they can both look like the following example: 
DEVICE=device_name
NAME=bond0-slave
TYPE=Ethernet
BOOTPROTO=none
ONBOOT=yes
MASTER=bond0
SLAVE=yes
NM_CONTROLLED="no"
In this example, replace device_name with the name of the interface. Note that if more than one profile or configuration file exists with ONBOOT=yes for an interface, they may race with each other and a plain TYPE=Ethernet profile may be activated instead of a bond port.

Note

Note that if the NM_CONTROLLED="no" setting is not present, NetworkManager might override settings in this configuration file.

7.4.4. Activating a Channel Bond

To activate a bond, open all the ports. As root, issue the following commands: 
~]# ifup ifcfg-enp1s0
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/7)
~]# ifup ifcfg-enp2s0
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/8)
Note that if editing interface files for interfaces which are currently “up”, set them down first as follows: 
ifdown device_name
Then when complete, open all the ports, which will open the bond (provided it was not set “down”).
To make NetworkManager aware of the changes, issue a command for every changed interface as root: 
~]# nmcli con load /etc/sysconfig/network-scripts/ifcfg-device
Alternatively, to reload all interfaces: 
~]# nmcli con reload
The default behavior is for NetworkManager not to be aware of the changes and to continue using the old configuration data. This is set by the monitor-connection-files option in the NetworkManager.conf file. See the NetworkManager.conf(5) manual page for more information.
To view the status of the bond interface, issue the following command: 
~]# ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp1s0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT qlen 1000
    link/ether 52:54:00:e9:ce:d2 brd ff:ff:ff:ff:ff:ff
3: enp2s0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT qlen 1000
    link/ether 52:54:00:38:a6:4c brd ff:ff:ff:ff:ff:ff
4: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT
    link/ether 52:54:00:38:a6:4c brd ff:ff:ff:ff:ff:ff

7.4.5. Creating Multiple Bonds

In Red Hat Enterprise Linux, for each bond a channel bonding interface is created including the BONDING_OPTS directive. This configuration method is used so that multiple bonding devices can have different configurations. To create multiple channel bonding interfaces, proceed as follows:
  • Create multiple ifcfg-bondN files with the BONDING_OPTS directive; this directive will cause the network scripts to create the bond interfaces as required.
  • Create, or edit existing, interface configuration files to be bonded and include the SLAVE directive.
  • Assign the interfaces to be bonded, the port interfaces, to the channel bonding interfaces by means of the MASTER directive.

Example 7.3. Example multiple ifcfg-bondN interface configuration files

The following is an example of a channel bonding interface configuration file: 
DEVICE=bondN
NAME=bondN
TYPE=Bond
BONDING_MASTER=yes
IPADDR=192.168.1.1
PREFIX=24
ONBOOT=yes
BOOTPROTO=none
BONDING_OPTS="bonding parameters separated by spaces"
In this example, replace N with the number for the bond interface. For example, to create two bonds create two configuration files, ifcfg-bond0 and ifcfg-bond1, with appropriate IP addresses.
Create the interfaces to be bonded as per Example 7.2, “Example Port Interface Configuration File” and assign them to the bond interfaces as required using the MASTER=bondN directive. For example, continuing on from the example above, if two interfaces per bond are required, then for two bonds create four interface configuration files and assign the first two using MASTER=bond0 and the next two using MASTER=bond1.

7.5. Verifying Network Configuration Bonding for Redundancy

Network redundancy is a process when devices are used for backup purposes to prevent or recover from a failure of a specific system. The following procedure describes how to verify the network configuration for bonding in redundancy:
Procedure
  1. Ping the destination IP from the bond interface. For example: 
    ~]# ping -I bond0 DSTADDR
  2. View which interface is in active mode: 
    ~]# cat /sys/class/net/bond0/bonding/active_slave
enp1s0
    enp1s0 is the active port interface.
  3. Set the active port interface down: 
    ~]# ip link set enp1s0 down
  4. Check if the backup interface is up: 
    ~]# cat /sys/class/net/bond0/bonding/active_slave
enp2s0
    enp2s0 is now the active port interface.
  5. Check if you can still ping the destination IP from the bond interface: 
    ~]# ping -I bond0 DSTADDR

7.6. Overview of Bonding Modes and the Required Settings on the Switch

The following table describes the required configuration that you must apply to the upstream switch depending on the bonding mode:
Table 7.1. Switch Configuration Settings Depending on the Bonding Modes
Bonding Mode Configuration on the Switch
0 - balance-rr Requires static Etherchannel enabled (not LACP-negotiated)
1 - active-backup Requires autonomous ports
2 - balance-xor Requires static Etherchannel enabled (not LACP-negotiated)
3 - broadcast Requires static Etherchannel enabled (not LACP-negotiated)
4 - 802.3ad Requires LACP-negotiated Etherchannel enabled
5 - balance-tlb Requires autonomous ports
6 - balance-alb Requires autonomous ports
For configuring these settings on your switch, see the switch documentation.

7.7. Using Channel Bonding

To enhance performance, adjust available module options to ascertain what combination works best. Pay particular attention to the miimon or arp_interval and the arp_ip_target parameters. See Section 7.7.1, “Bonding Module Directives” for a list of available options and how to quickly determine the best ones for your bonded interface.

7.7.1. Bonding Module Directives

It is a good idea to test which channel bonding module parameters work best for your bonded interfaces before adding them to the BONDING_OPTS="bonding parameters" directive in your bonding interface configuration file (ifcfg-bond0 for example). Parameters to bonded interfaces can be configured without unloading (and reloading) the bonding module by manipulating files in the sysfs file system.
sysfs is a virtual file system that represents kernel objects as directories, files and symbolic links. sysfs can be used to query for information about kernel objects, and can also manipulate those objects through the use of normal file system commands. The sysfs virtual file system is mounted under the /sys/ directory. All bonding interfaces can be configured dynamically by interacting with and manipulating files under the /sys/class/net/ directory.
In order to determine the best parameters for your bonding interface, create a channel bonding interface file such as ifcfg-bond0 by following the instructions in Section 7.4.2, “Create a Channel Bonding Interface”. Insert the SLAVE=yes and MASTER=bond0 directives in the configuration files for each interface bonded to bond0. Once this is completed, you can proceed to testing the parameters.
First, open the bond you created by running ifup bondN as root: 
~]# ifup bond0
If you have correctly created the ifcfg-bond0 bonding interface file, you will be able to see bond0 listed in the output of running ip link show as root: 
~]# ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp1s0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT qlen 1000
    link/ether 52:54:00:e9:ce:d2 brd ff:ff:ff:ff:ff:ff
3: enp2s0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT qlen 1000
    link/ether 52:54:00:38:a6:4c brd ff:ff:ff:ff:ff:ff
4: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT
    link/ether 52:54:00:38:a6:4c brd ff:ff:ff:ff:ff:ff
To view all existing bonds, even if they are not up, run: 
~]$ cat /sys/class/net/bonding_masters
bond0
You can configure each bond individually by manipulating the files located in the /sys/class/net/bondN/bonding/ directory. First, the bond you are configuring must be taken down: 
~]# ifdown bond0
As an example, to enable MII monitoring on bond0 with a 1 second interval, run as root: 
~]# echo 1000 > /sys/class/net/bond0/bonding/miimon
To configure bond0 for balance-alb mode, run either: 
~]# echo 6 > /sys/class/net/bond0/bonding/mode
...or, using the name of the mode: 
~]# echo balance-alb > /sys/class/net/bond0/bonding/mode
After configuring options for the bond in question, you can bring it up and test it by running ifup bondN. If you decide to change the options, take the interface down, modify its parameters using sysfs, bring it back up, and re-test.
Once you have determined the best set of parameters for your bond, add those parameters as a space-separated list to the BONDING_OPTS= directive of the /etc/sysconfig/network-scripts/ifcfg-bondN file for the bonding interface you are configuring. Whenever that bond is brought up (for example, by the system during the boot sequence if the ONBOOT=yes directive is set), the bonding options specified in the BONDING_OPTS will take effect for that bond.
The following list provides the names of many of the more common channel bonding parameters, along with a description of what they do. For more information, see the brief descriptions for each parm in modinfo bonding output, or for more detailed information, see https://www.kernel.org/doc/Documentation/networking/bonding.txt.

Bonding Interface Parameters

ad_select=value
Specifies the 802.3ad aggregation selection logic to use. Possible values are:
  • stable or 0 — Default setting. The active aggregator is chosen by largest aggregate bandwidth. Reselection of the active aggregator occurs only when all ports of the active aggregator are down or if the active aggregator has no ports.
  • bandwidth or 1 — The active aggregator is chosen by largest aggregate bandwidth. Reselection occurs if:
    • A port is added to or removed from the bond;
    • Any port's link state changes;
    • Any port's 802.3ad association state changes;
    • The bond's administrative state changes to up.
  • count or 2 — The active aggregator is chosen by the largest number of ports. Reselection occurs as described for the bandwidth setting above.
The bandwidth and count selection policies permit failover of 802.3ad aggregations when partial failure of the active aggregator occurs. This keeps the aggregator with the highest availability, either in bandwidth or in number of ports, active at all times.
arp_interval=time_in_milliseconds
Specifies, in milliseconds, how often ARP monitoring occurs.

Important

It is essential that both arp_interval and arp_ip_target parameters are specified, or, alternatively, the miimon parameter is specified. Failure to do so can cause degradation of network performance in the event that a link fails.
If using this setting while in mode=0 or mode=2 (the two load-balancing modes), the network switch must be configured to distribute packets evenly across the NICs. For more information on how to accomplish this, see https://www.kernel.org/doc/Documentation/networking/bonding.txt.
The value is set to 0 by default, which disables it.
arp_ip_target=ip_address[,ip_address_2,…ip_address_16]
Specifies the target IP address of ARP requests when the arp_interval parameter is enabled. Up to 16 IP addresses can be specified in a comma separated list.
arp_validate=value
Validate source/distribution of ARP probes; default is none. Other valid values are active, backup, and all.
downdelay=time_in_milliseconds
Specifies (in milliseconds) how long to wait after link failure before disabling the link. The value must be a multiple of the value specified in the miimon parameter. The value is set to 0 by default, which disables it.
fail_over_mac=value
Specifies whether active-backup mode should set all ports to the same MAC address at the point of assignment (the traditional behavior), or, when enabled, perform special handling of the bond's MAC address in accordance with the selected policy. Possible values are:
  • none or 0 — Default setting. This setting disables fail_over_mac, and causes bonding to set all ports of an active-backup bond to the same MAC address at the point of assignment.
  • active or 1 — The “active” fail_over_mac policy indicates that the MAC address of the bond should always be the MAC address of the currently active port. The MAC address of the ports is not changed; instead, the MAC address of the bond changes during a failover.
    This policy is useful for devices that cannot ever alter their MAC address, or for devices that refuse incoming broadcasts with their own source MAC (which interferes with the ARP monitor). The disadvantage of this policy is that every device on the network must be updated by gratuitous ARP, as opposed to the normal method of switches snooping incoming traffic to update their ARP tables. If the gratuitous ARP is lost, communication may be disrupted.
    When this policy is used in conjunction with the MII monitor, devices which assert link up prior to being able to actually transmit and receive are particularly susceptible to loss of the gratuitous ARP, and an appropriate updelay setting may be required.
  • follow or 2 — The “follow” fail_over_mac policy causes the MAC address of the bond to be selected normally (normally the MAC address of the first port added to the bond). However, the second and subsequent ports are not set to this MAC address while they are in a backup role; a port is programmed with the bond's MAC address at failover time (and the formerly active port receives the newly active port's MAC address).
    This policy is useful for multiport devices that either become confused or incur a performance penalty when multiple ports are programmed with the same MAC address.
lacp_rate=value
Specifies the rate at which link partners should transmit LACPDU packets in 802.3ad mode. Possible values are:
  • slow or 0 — Default setting. This specifies that partners should transmit LACPDUs every 30 seconds.
  • fast or 1 — Specifies that partners should transmit LACPDUs every 1 second.
miimon=time_in_milliseconds
Specifies (in milliseconds) how often MII link monitoring occurs. This is useful if high availability is required because MII is used to verify that the NIC is active. To verify that the driver for a particular NIC supports the MII tool, type the following command as root: 
~]# ethtool interface_name | grep "Link detected:"
In this command, replace interface_name with the name of the device interface, such as enp1s0, not the bond interface. If MII is supported, the command returns: 
Link detected: yes
If using a bonded interface for high availability, the module for each NIC must support MII. Setting the value to 0 (the default), turns this feature off. When configuring this setting, a good starting point for this parameter is 100.

Important

It is essential that both arp_interval and arp_ip_target parameters are specified, or, alternatively, the miimon parameter is specified. Failure to do so can cause degradation of network performance in the event that a link fails.
mode=value
Allows you to specify the bonding policy. The value can be one of:
  • balance-rr or 0 — Sets a round-robin policy for fault tolerance and load balancing. Transmissions are received and sent out sequentially on each bonded port interface beginning with the first one available.
  • active-backup or 1 — Sets an active-backup policy for fault tolerance. Transmissions are received and sent out through the first available bonded port interface. Another bonded port interface is only used if the active bonded port interface fails.
  • balance-xor or 2 — Transmissions are based on the selected hash policy. The default is to derive a hash by XOR of the source and destination MAC addresses multiplied by the modulo of the number of port interfaces. In this mode traffic destined for specific peers will always be sent over the same interface. As the destination is determined by the MAC addresses this method works best for traffic to peers on the same link or local network. If traffic has to pass through a single router then this mode of traffic balancing will be suboptimal.
  • broadcast or 3 — Sets a broadcast policy for fault tolerance. All transmissions are sent on all port interfaces.
  • 802.3ad or 4 — Sets an IEEE 802.3ad dynamic link aggregation policy. Creates aggregation groups that share the same speed and duplex settings. Transmits and receives on all ports in the active aggregator. Requires a switch that is 802.3ad compliant.
  • balance-tlb or 5 — Sets a Transmit Load Balancing (TLB) policy for fault tolerance and load balancing. The outgoing traffic is distributed according to the current load on each port interface. Incoming traffic is received by the current port. If the receiving port fails, another port takes over the MAC address of the failed port. This mode is only suitable for local addresses known to the kernel bonding module and therefore cannot be used behind a bridge with virtual machines.
  • balance-alb or 6 — Sets an Adaptive Load Balancing (ALB) policy for fault tolerance and load balancing. Includes transmit and receive load balancing for IPv4 traffic. Receive load balancing is achieved through ARP negotiation. This mode is only suitable for local addresses known to the kernel bonding module and therefore cannot be used behind a bridge with virtual machines.
For details about required settings on the upstream switch, see Section 7.6, “Overview of Bonding Modes and the Required Settings on the Switch”.
primary=interface_name
Specifies the interface name, such as enp1s0, of the primary device. The primary device is the first of the bonding interfaces to be used and is not abandoned unless it fails. This setting is particularly useful when one NIC in the bonding interface is faster and, therefore, able to handle a bigger load.
This setting is only valid when the bonding interface is in active-backup mode. See https://www.kernel.org/doc/Documentation/networking/bonding.txt for more information.
primary_reselect=value
Specifies the reselection policy for the primary port. This affects how the primary port is chosen to become the active port when failure of the active port or recovery of the primary port occurs. This parameter is designed to prevent flip-flopping between the primary port and other ports. Possible values are:
  • always or 0 (default) — The primary port becomes the active port whenever it comes back up.
  • better or 1 — The primary port becomes the active port when it comes back up, if the speed and duplex of the primary port is better than the speed and duplex of the current active port.
  • failure or 2 — The primary port becomes the active port only if the current active port fails and the primary port is up.
The primary_reselect setting is ignored in two cases:
  • If no ports are active, the first port to recover is made the active port.
  • When initially assigned to a bond, the primary port is always made the active port.
Changing the primary_reselect policy through sysfs will cause an immediate selection of the best active port according to the new policy. This may or may not result in a change of the active port, depending upon the circumstances
resend_igmp=range
Specifies the number of IGMP membership reports to be issued after a failover event. One membership report is issued immediately after the failover, subsequent packets are sent in each 200ms interval.
The valid range is 0 to 255; the default value is 1. A value of 0 prevents the IGMP membership report from being issued in response to the failover event.
This option is useful for bonding modes balance-rr (mode 0), active-backup (mode 1), balance-tlb (mode 5) and balance-alb (mode 6), in which a failover can switch the IGMP traffic from one port to another. Therefore a fresh IGMP report must be issued to cause the switch to forward the incoming IGMP traffic over the newly selected port.
updelay=time_in_milliseconds
Specifies (in milliseconds) how long to wait before enabling a link. The value must be a multiple of the value specified in the miimon parameter. The value is set to 0 by default, which disables it.
use_carrier=number
Specifies whether or not miimon should use MII/ETHTOOL ioctls or netif_carrier_ok() to determine the link state. The netif_carrier_ok() function relies on the device driver to maintains its state with netif_carrier_on/off; most device drivers support this function.
The MII/ETHTOOL ioctls tools utilize a deprecated calling sequence within the kernel. However, this is still configurable in case your device driver does not support netif_carrier_on/off.
Valid values are:
  • 1 — Default setting. Enables the use of netif_carrier_ok().
  • 0 — Enables the use of MII/ETHTOOL ioctls.

Note

If the bonding interface insists that the link is up when it should not be, it is possible that your network device driver does not support netif_carrier_on/off.
xmit_hash_policy=value
Selects the transmit hash policy used for port selection in balance-xor and 802.3ad modes. Possible values are:
  • 0 or layer2 — Default setting. This parameter uses the XOR of hardware MAC addresses to generate the hash. The formula used is: 
    (source_MAC_address XOR destination_MAC) MODULO slave_count
    This algorithm will place all traffic to a particular network peer on the same port, and is 802.3ad compliant.
  • 1 or layer3+4 — Uses upper layer protocol information (when available) to generate the hash. This allows for traffic to a particular network peer to span multiple ports, although a single connection will not span multiple ports.
    The formula for unfragmented TCP and UDP packets used is: 
    ((source_port XOR dest_port) XOR
  ((source_IP XOR dest_IP) AND 0xffff)
    MODULO slave_count
    For fragmented TCP or UDP packets and all other IP protocol traffic, the source and destination port information is omitted. For non-IP traffic, the formula is the same as the layer2 transmit hash policy.
    This policy intends to mimic the behavior of certain switches; particularly, Cisco switches with PFC2 as well as some Foundry and IBM products.
    The algorithm used by this policy is not 802.3ad compliant.
  • 2 or layer2+3 — Uses a combination of layer2 and layer3 protocol information to generate the hash.
    Uses XOR of hardware MAC addresses and IP addresses to generate the hash. The formula is: 
    (((source_IP XOR dest_IP) AND 0xffff) XOR
  ( source_MAC XOR destination_MAC ))
    MODULO slave_count
    This algorithm will place all traffic to a particular network peer on the same port. For non-IP traffic, the formula is the same as for the layer2 transmit hash policy.
    This policy is intended to provide a more balanced distribution of traffic than layer2 alone, especially in environments where a layer3 gateway device is required to reach most destinations.
    This algorithm is 802.3ad compliant.

7.8. Creating a Bond Connection Using a GUI

You can use the GNOME control-center utility to direct NetworkManager to create a Bond from two or more Wired or InfiniBand connections. It is not necessary to create the connections to be bonded first. They can be configured as part of the process to configure the bond. You must have the MAC addresses of the interfaces available in order to complete the configuration process.

7.8.1. Establishing a Bond Connection

Procedure 7.1. Adding a New Bond Connection_Using nm-connection-editor

Follow the below steps to create a new bond connection.
  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
  2. Click the Add button. The Choose a Connection Type window appears. Select Bond and click Create. The Editing Bond connection 1 window appears.
    The NetworkManager Graphical User Interface Add a Bond menu

    Figure 7.6. The NetworkManager Graphical User Interface Add a Bond menu

  3. On the Bond tab, click Add and select the type of interface you want to use with the bond connection. Click the Create button. Note that the dialog to select the port type only comes up when you create the first port; after that, it will automatically use that same type for all further ports.
  4. The Editing bond0 slave 1 window appears. Use the Device MAC address drop-down menu to select the MAC address of the interface to be bonded. The first port's MAC address will be used as the MAC address for the bond interface. If required, enter a clone MAC address to be used as the bond's MAC address. Click the Save button.
    The NetworkManager Graphical User Interface Add a Bond Connection menu

    Figure 7.7. The NetworkManager Graphical User Interface Add a Bond Connection menu

  5. The name of the bonded port appears in the Bonded connections window. Click the Add button to add further port connections.
  6. Review and confirm the settings and then click the Save button.
  7. Edit the bond-specific settings by referring to Section 7.8.1.1, “Configuring the Bond Tab” below.

Procedure 7.2. Editing an Existing Bond Connection

Follow these steps to edit an existing bond connection.
  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
  2. Select the connection you want to edit and click the Edit button.
  3. Select the General tab.
  4. Configure the connection name, auto-connect behavior, and availability settings.
    Five settings in the Editing dialog are common to all connection types, see the General tab:
    • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the menu of the Network window.
    • Automatically connect to this network when it is available — Select this box if you want NetworkManager to auto-connect to this connection when it is available. See the section called “Editing an Existing Connection with control-center” for more information.
    • All users may connect to this network — Select this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 3.4.5, “Managing System-wide and Private Connection Profiles with a GUI” for details.
    • Automatically connect to VPN when using this connection — Select this box if you want NetworkManager to auto-connect to a VPN connection when it is available. Select the VPN from the drop-down menu.
    • Firewall Zone — Select the firewall zone from the drop-down menu. See the Red Hat Enterprise Linux 7 Security Guide for more information on firewall zones.
  5. Edit the bond-specific settings by referring to Section 7.8.1.1, “Configuring the Bond Tab” below.
Saving Your New (or Modified) Connection and Making Further Configurations
Once you have finished editing your bond connection, click the Save button to save your customized configuration.
Then, to configure:
7.8.1.1. Configuring the Bond Tab
If you have already added a new bond connection (see Procedure 7.1, “Adding a New Bond Connection_Using nm-connection-editor” for instructions), you can edit the Bond tab to set the load sharing mode and the type of link monitoring to use to detect failures of a port connection.
Mode
The mode that is used to share traffic over the port connections which make up the bond. The default is Round-robin. Other load sharing modes, such as 802.3ad, can be selected by means of the drop-down list.
Link Monitoring
The method of monitoring the ports ability to carry network traffic.
The following modes of load sharing are selectable from the Mode drop-down list:
Round-robin
Sets a round-robin policy for fault tolerance and load balancing. Transmissions are received and sent out sequentially on each bonded port interface beginning with the first one available. This mode might not work behind a bridge with virtual machines without additional switch configuration.
Active backup
Sets an active-backup policy for fault tolerance. Transmissions are received and sent out through the first available bonded port interface. Another bonded port interface is only used if the active bonded port interface fails. Note that this is the only mode available for bonds of InfiniBand devices.
XOR
Sets an XOR (exclusive-or) policy. Transmissions are based on the selected hash policy. The default is to derive a hash by XOR of the source and destination MAC addresses multiplied by the modulo of the number of port interfaces. In this mode traffic destined for specific peers will always be sent over the same interface. As the destination is determined by the MAC addresses this method works best for traffic to peers on the same link or local network. If traffic has to pass through a single router then this mode of traffic balancing will be suboptimal.
Broadcast
Sets a broadcast policy for fault tolerance. All transmissions are sent on all port interfaces. This mode might not work behind a bridge with virtual machines without additional switch configuration.
802.3ad
Sets an IEEE 802.3ad dynamic link aggregation policy. Creates aggregation groups that share the same speed and duplex settings. Transmits and receives on all ports in the active aggregator. Requires a network switch that is 802.3ad compliant.
Adaptive transmit load balancing
Sets an adaptive Transmit Load Balancing (TLB) policy for fault tolerance and load balancing. The outgoing traffic is distributed according to the current load on each port interface. Incoming traffic is received by the current port. If the receiving port fails, another port takes over the MAC address of the failed port. This mode is only suitable for local addresses known to the kernel bonding module and therefore cannot be used behind a bridge with virtual machines.
Adaptive load balancing
Sets an Adaptive Load Balancing (ALB) policy for fault tolerance and load balancing. Includes transmit and receive load balancing for IPv4 traffic. Receive load balancing is achieved through ARP negotiation. This mode is only suitable for local addresses known to the kernel bonding module and therefore cannot be used behind a bridge with virtual machines.
The following types of link monitoring can be selected from the Link Monitoring drop-down list. It is a good idea to test which channel bonding module parameters work best for your bonded interfaces.
MII (Media Independent Interface)
The state of the carrier wave of the interface is monitored. This can be done by querying the driver, by querying MII registers directly, or by using ethtool to query the device. Three options are available:
Monitoring Frequency
The time interval, in milliseconds, between querying the driver or MII registers.
Link up delay
The time in milliseconds to wait before attempting to use a link that has been reported as up. This delay can be used if some gratuitous ARP requests are lost in the period immediately following the link being reported as “up”. This can happen during switch initialization for example.
Link down delay
The time in milliseconds to wait before changing to another link when a previously active link has been reported as “down”. This delay can be used if an attached switch takes a relatively long time to change to backup mode.
ARP
The address resolution protocol (ARP) is used to probe one or more peers to determine how well the link-layer connections are working. It is dependent on the device driver providing the transmit start time and the last receive time.
Two options are available:
Monitoring Frequency
The time interval, in milliseconds, between sending ARP requests.
ARP targets
A comma separated list of IP addresses to send ARP requests to.

7.9. Additional Resources

Installed Documentation

  • nmcli(1) man page — Describes NetworkManager's command‐line tool.
  • nmcli-examples(5) man page — Gives examples of nmcli commands.
  • nm-settings(5) man page — Description of settings and parameters of NetworkManager connections.

Online Documentation

Red Hat Enterprise Linux System Administrator's Guide
Explains the use of kernel module capabilities.
https://access.redhat.com/site/node/28421/Configuring_VLAN_devices_over_a_bonded_interface
A Red Hat Knowledgebase article about Configuring VLAN devices over a bonded interface.

Chapter 8. Configure Network Teaming

8.1. Understanding Network Teaming

The combining or aggregating of network links to provide a logical link with higher throughput, or to provide redundancy, is known by many names, for example channel bonding, Ethernet bonding, port trunking, channel teaming, NIC teaming, or link aggregation. This concept as originally implemented in the Linux kernel is widely referred to as bonding. The term Network Teaming has been chosen to refer to this new implementation of the concept. The existing bonding driver is unaffected, Network Teaming is offered as an alternative and does not replace bonding in Red Hat Enterprise Linux 7.

Note

Regarding the Mode 4 Link Aggregation Control Protocol (LACP) teaming mode, requires configuring the switch to aggregate the links. For more details, see https://www.kernel.org/doc/Documentation/networking/bonding.txt
Network Teaming, or Team, is designed to implement the concept in a different way by providing a small kernel driver to implement the fast handling of packet flows, and various user-space applications to do everything else in user space. The driver has an Application Programming Interface (API), referred to as “Team Netlink API”, which implements Netlink communications. User-space applications can use this API to communicate with the driver. A library, referred to as “lib”, has been provided to do user space wrapping of Team Netlink communications and RT Netlink messages. An application daemon, teamd, which uses the libteam library is also available. One instance of teamd can control one instance of the Team driver. The daemon implements the load-balancing and active-backup logic, such as round-robin, by using additional code referred to as “runners”. By separating the code in this way, the Network Teaming implementation presents an easily extensible and scalable solution for load-balancing and redundancy requirements. For example, custom runners can be relatively easily written to implement new logic through teamd, and even teamd is optional, users can write their own application to use libteam.
The teamdctl utility is available to control a running instance of teamd using D-bus. teamdctl provides a D-Bus wrapper around the teamd D-Bus API. By default, teamd listens and communicates using Unix Domain Sockets but still monitors D-Bus. This is to ensure that teamd can be used in environments where D-Bus is not present or not yet loaded. For example, when booting over teamd links, D-Bus would not yet be loaded. The teamdctl utility can be used during run time to read the configuration, the state of link-watchers, check and change the state of ports, add and remove ports, and to change ports between active and backup states.
Team Netlink API communicates with user-space applications using Netlink messages. The libteam user-space library does not directly interact with the API, but uses libnl or teamnl to interact with the driver API.
To sum up, the instances of Team driver, running in the kernel, do not get configured or controlled directly. All configuration is done with the aid of user space applications, such as the teamd application. The application then directs the kernel driver part accordingly.

Note

In the context of network teaming, the term port is also known as slave. Port is preferred when using teamd directly while slave is used when using NetworkManager to refer to interfaces which create a team.

8.2. Understanding the Default Behavior of Controller and Port Interfaces

When controlling teamed port interfaces using the NetworkManager daemon, and especially when fault finding, keep the following in mind:
  1. Starting the controller interface does not automatically start the port interfaces.
  2. Starting a port interface always starts the controller interface.
  3. Stopping the controller interface also stops the port interfaces.
  4. A controller without ports can start static IP connections.
  5. A controller without ports waits for ports when starting DHCP connections.
  6. A controller with a DHCP connection waiting for ports completes when a port with a carrier is added.
  7. A controller with a DHCP connection waiting for ports continues waiting when a port without a carrier is added.

Warning

The use of direct cable connections without network switches is not supported for teaming. The failover mechanisms described here will not work as expected without the presence of network switches. See the Red Hat Knowledgebase article Why is bonding not supported with direct connection using crossover cables? for more information.

8.3. Comparison of Network Teaming to Bonding

Table 8.1. A Comparison of Features in Bonding and Team
FeatureBondingTeam
broadcast Tx policyYesYes
round-robin Tx policyYesYes
active-backup Tx policyYesYes
LACP (802.3ad) supportYes (active only)Yes
Hash-based Tx policyYesYes
User can set hash functionNoYes
Tx load-balancing support (TLB)YesYes
LACP hash port selectYesYes
load-balancing for LACP supportNoYes
Ethtool link monitoringYesYes
ARP link monitoringYesYes
NS/NA (IPv6) link monitoringNoYes
ports up/down delaysYesYes
port priorities and stickiness (“primary” option enhancement)NoYes
separate per-port link monitoring setupNoYes
multiple link monitoring setupLimitedYes
lockless Tx/Rx pathNo (rwlock)Yes (RCU)
VLAN supportYesYes
user-space runtime controlLimitedFull
Logic in user-spaceNoYes
ExtensibilityHardEasy
Modular designNoYes
Performance overheadLowVery Low
D-Bus interfaceNoYes
multiple device stackingYesYes
zero config using LLDPNo(in planning)
NetworkManager supportYesYes

8.4. Understanding the Network Teaming Daemon and the "Runners"

The Team daemon, teamd, uses libteam to control one instance of the team driver. This instance of the team driver adds instances of a hardware device driver to form a “team” of network links. The team driver presents a network interface, team0 for example, to the other parts of the kernel. The interfaces created by instances of the team driver are given names such as team0, team1, and so forth in the documentation. This is for ease of understanding and other names can be used. The logic common to all methods of teaming is implemented by teamd; those functions that are unique to the different load sharing and backup methods, such as round-robin, are implemented by separate units of code referred to as “runners”. Because words such as “module” and “mode” already have specific meanings in relation to the kernel, the word “runner” was chosen to refer to these units of code. The user specifies the runner in the JSON format configuration file and the code is then compiled into an instance of teamd when the instance is created. A runner is not a plug-in because the code for a runner is compiled into an instance of teamd as it is being created. Code could be created as a plug-in for teamd should the need arise.
The following runners are available at time of writing.
  • broadcast (data is transmitted over all ports)
  • round-robin (data is transmitted over all ports in turn)
  • active-backup (one port or link is used while others are kept as a backup)
  • loadbalance (with active Tx load balancing and BPF-based Tx port selectors)
  • lacp (implements the 802.3ad Link Aggregation Control Protocol)
In addition, the following link-watchers are available:
  • ethtool (Libteam lib uses ethtool to watch for link state changes). This is the default if no other link-watcher is specified in the configuration file.
  • arp_ping (The arp_ping utility is used to monitor the presence of a far-end hardware address using ARP packets.)
  • nsna_ping (Neighbor Advertisements and Neighbor Solicitation from the IPv6 Neighbor Discovery protocol are used to monitor the presence of a neighbor's interface)
There are no restrictions in the code to prevent a particular link-watcher from being used with a particular runner, however when using the lacp runner, ethtool is the only recommended link-watcher.

8.5. Install the Network Teaming Daemon

The networking teaming daemon, teamd, is not installed by default. To install teamd, issue the following command as root: 
~]# yum install teamd

8.6. Converting a Bond to a Team

It is possible to convert existing bonding configuration files to team configuration files using the bond2team tool. It can convert bond configuration files in ifcfg format to team configuration files in either ifcfg or JSON format. Note that firewall rules, alias interfaces, and anything that might be tied to the original interface name can break after the renaming because the tool will only change the ifcfg file, nothing else.
To see some examples of the command format, issue the following command: 
~]$ bond2team --examples
New files will be created in a directory whose name starts with /tmp/bond2team.XXXXXX/, where XXXXXX is a random string. After creating the new configuration files, move the old bonding files to a backup folder and then move the new files to the /etc/sysconfig/network-scripts/ directory.

Example 8.1. Convert a Bond to a Team

To convert a current bond0 configuration to team ifcfg, issue a command as root: 
~]# /usr/bin/bond2team --master bond0
Note that this will retain the name bond0. To use a new name to save the configuration, use the --rename as follows: 
~]# /usr/bin/bond2team --master bond0 --rename team0
add the --json option to output JSON format files instead of ifcfg files. See the teamd.conf(5) man page for examples of JSON format.

Example 8.2. Convert a Bond to a Team and Specify the File Path

To convert a current bond0 configuration to team ifcfg, and to manually specify the path to the ifcfg file, issue a command as root: 
~]# /usr/bin/bond2team --master bond0 --configdir /path/to/ifcfg-file
add the --json option to output JSON format files instead of ifcfg files.

Example 8.3. Create a Team Configuration Using Bond2team

It is also possible to create a team configuration by supplying the bond2team tool with a list of bonding parameters. For example: 
~]# /usr/bin/bond2team --bonding_opts "mode=1 miimon=500"
Ports can also be supplied on the command line as follows: 
~]# /usr/bin/bond2team --bonding_opts "mode=1 miimon=500 primary=enp1s0 \
  primary_reselect-0" --port enp1s0 --port enp2s0 --port enp3s0 --port enp4s0
See the bond2team(1) man page for further details. For an explanation of bonding parameters, see Section 7.7, “Using Channel Bonding”

8.7. Selecting Interfaces to Use as Ports for a Network Team

To view the available interfaces, issue the following command: 
~]$ ip link show
1: lo:  <LOOPBACK,UP,LOWER_UP > mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: em1:  <BROADCAST,MULTICAST,UP,LOWER_UP > mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
    link/ether 52:54:00:6a:02:8a brd ff:ff:ff:ff:ff:ff
3: em2:  <BROADCAST,MULTICAST,UP,LOWER_UP > mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
link/ether 52:54:00:9b:6d:2a brd ff:ff:ff:ff:ff:ff
From the available interfaces, determine which are suitable for adding to your network team and then proceed to Section 8.8, “Selecting Network Team Configuration Methods”

8.8. Selecting Network Team Configuration Methods

To configure a network team using NetworkManager's text user interface tool, nmtui, proceed to Section 8.9, “Configure a Network Team Using the Text User Interface, nmtui”
To create a network team using the command-line tool, nmcli, proceed to Section 8.10.1, “Configure Network Teaming Using nmcli”.
To create a network team using the Team daemon, teamd, proceed to Section 8.10.2, “Creating a Network Team Using teamd”.
To create a network team using configuration files, proceed to Section 8.10.3, “Creating a Network Team Using ifcfg Files”.
To configure a network team using a graphical user interface, see Section 8.14, “Creating a Network Team Using a GUI”

8.9. Configure a Network Team Using the Text User Interface, nmtui

The text user interface tool nmtui can be used to configure teaming in a terminal window. Issue the following command to start the tool: 
~]$ nmtui
The text user interface appears. Any invalid command prints a usage message.
To navigate, use the arrow keys or press Tab to step forwards and press Shift+Tab to step back through the options. Press Enter to select an option. The Space bar toggles the status of a check box.
  1. From the starting menu, select Edit a connection. Select Add, the New Connection screen opens.
    The NetworkManager Text User Interface Add a Team Connection menu

    Figure 8.1. The NetworkManager Text User Interface Add a Team Connection menu

  2. Select Team, the Edit connection screen opens.
    The NetworkManager Text User Interface Configuring a Team Connection menu

    Figure 8.2. The NetworkManager Text User Interface Configuring a Team Connection menu

  3. To add port interfaces to the team select Add, the New Connection screen opens. Once the type of Connection has been chosen select the Create button to cause the team's Edit Connection display to appear.
    The NetworkManager Text User Interface Configuring a new Team Port Interface Connection menu

    Figure 8.3. The NetworkManager Text User Interface Configuring a new Team Port Interface Connection menu

  4. Enter the required port's device name or MAC address in the Device section. If required, enter a clone MAC address to be used as the team's MAC address by selecting Show to the right of the Ethernet label. Select the OK button.

    Note

    If the device is specified without a MAC address the Device section will be automatically populated once the Edit Connection window is reloaded, but only if it successfully finds the device.
    The NetworkManager Text User Interface Configuring a Team's Port Interface Connection menu

    Figure 8.4. The NetworkManager Text User Interface Configuring a Team's Port Interface Connection menu

  5. The name of the teamed port appears in the Slaves section. Repeat the above steps to add further port connections.
  6. If custom port settings are to be applied select the Edit button under the JSON configuration section. This will launch a vim console where changes may be applied. Once finished write the changes from vim and then confirm that the displayed JSON string under JSON configuration matches what is intended.
  7. Review and confirm the settings before selecting the OK button.
    The NetworkManager Text User Interface Configuring a Team Connection menu

    Figure 8.5. The NetworkManager Text User Interface Configuring a Team Connection menu

See Section 8.13, “Configure teamd Runners” for examples of JSON strings. Note that only the relevant sections from the example strings should be used for a team or port configuration using nmtui. Do not specify the “Device” as part of the JSON string. For example, only the JSON string after “device” but before “port” should be used in the Team JSON configuration field. All JSON strings relevant to a port must only be added in the port configuration field.
See Section 3.2, “Configuring IP Networking with nmtui” for information on installing nmtui.

8.10. Configure a Network Team Using the Command Line

8.10.1. Configure Network Teaming Using nmcli

To view the connections available on the system: 
~]$ nmcli connection show
NAME  UUID                                  TYPE            DEVICE
enp2s0  0e8185a1-f0fd-4802-99fb-bedbb31c689b  802-3-ethernet  --
enp1s0  dfe1f57b-419d-4d1c-aaf5-245deab82487  802-3-ethernet  --
To view the devices available on the system: 
~]$ nmcli device status
DEVICE      TYPE      STATE                                  CONNECTION
virbr0      bridge    connected                              virbr0
ens3        ethernet  connected                              ens3
To create a new team interface, with name ServerA: 
~]$ nmcli connection add type team ifname ServerA
Connection 'team-ServerA' (b954c62f-5fdd-4339-97b0-40efac734c50) successfully added.
NetworkManager will set its internal parameter connection.autoconnect to yes and as no IP address was given ipv4.method will be set to auto. NetworkManager will also write a configuration file to /etc/sysconfig/network-scripts/ifcfg-team-ServerA where the corresponding ONBOOT will be set to yes and BOOTPROTO will be set to dhcp.
Note that manual changes to the ifcfg file will not be noticed by NetworkManager until the interface is next brought up. See Section 2.7, “Using NetworkManager with sysconfig files” for more information on using configuration files.
To view the other values assigned: 
~]$ nmcli con show team-ServerA
connection.id:                          team-ServerA
connection.uuid:                        b954c62f-5fdd-4339-97b0-40efac734c50
connection.interface-name:              ServerA
connection.type:                        team
connection.autoconnect:                 yes
…
ipv4.method:                            auto
[output truncated]
As no JSON configuration file was specified the default values apply. See the teamd.conf(5) man page for more information on the team JSON parameters and their default values. Notice that the name was derived from the interface name by prepending the type. Alternatively, specify a name with the con-name option as follows: 
~]$ nmcli connection add type team con-name Team0 ifname ServerB
Connection 'Team0' (5f7160a1-09f6-4204-8ff0-6d96a91218a7) successfully added.
To view the team interfaces just configured, enter a command as follows: 
~]$ nmcli con show
NAME                UUID                                  TYPE            DEVICE
team-ServerA        b954c62f-5fdd-4339-97b0-40efac734c50  team            ServerA
enp2s0                0e8185a1-f0fd-4802-99fb-bedbb31c689b  802-3-ethernet  --
enp1s0                dfe1f57b-419d-4d1c-aaf5-245deab82487  802-3-ethernet  --
Team0               5f7160a1-09f6-4204-8ff0-6d96a91218a7  team            ServerB
To change the name assigned to a team, enter a command in the following format: 
nmcli con mod old-team-name connection.id new-team-name
To load a team configuration file for a team that already exists: 
nmcli connection modify team-name team.config JSON-config
You can specify the team configuration either as a JSON string or provide a file name containing the configuration. The file name can include the path. In both cases, what is stored in the team.config property is the JSON string. In the case of a JSON string, use single quotes around the string and paste the entire string to the command line.
To review the team.config property: 
nmcli con show team-name | grep team.config
When the team.config property is set, all the other team properties are updated accordingly.
It is also possible a more flexible way of exposing and setting particular team options without modifying directly the corresponding JSON string. You can do this by using the other available team properties to set the related team options one by one to the required values. As a result, the team.config property is updated to match the new values.
For example, to set the team.link-watchers property which allows to specify one or multiple link-watchers, enter a command in the following format: 
nmcli connection modify team-name team.link-watchers "name=ethtool delay-up=5, name=nsna_ping target-host=target.host"
The required link-watchers are separated by comma and the attributes which belong to the same link-watcher are separated by space.
To set the team.runner and the team.link-watchers properties, enter a command in the following format: 
nmcli connection modify team-name team.runner activebackup team.link-watchers "name=ethtool delay-up=5, name=nsna_ping target-host=target.host"
This is equivalent to set the team.config property to the corresponding JSON string: 
nmcli connection modify team-name team.config '{"runner": {"name": "activebackup"}, "link_watch": [{"name": "ethtool", "delay_up": 5},{"name": "nsna_ping", "target_host ": "target.host"}]'
To add an interface enp1s0 to Team0, with the name Team0-port1, issue a command as follows: 
~]$ nmcli con add type ethernet con-name Team0-port1 ifname enp1s0 slave-type team master Team0
Connection 'Team0-port1' (ccd87704-c866-459e-8fe7-01b06cf1cffc) successfully added.
Similarly, to add another interface, enp2s0, with the name Team0-port2, issue a command as follows: 
~]$ nmcli con add type ethernet con-name Team0-port2 ifname enp2s0 slave-type team master Team0
Connection 'Team0-port2' (a89ccff8-8202-411e-8ca6-2953b7db52dd) successfully added.
nmcli only supports Ethernet ports.
To open a team, the ports must be brought up first as follows: 
~]$ nmcli connection up Team0-port1
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/2)
~]$ nmcli connection up Team0-port2
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/3)
You can verify that the team interface was brought up by the activation of the ports, as follows: 
~]$ ip link
3:  Team0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT
    link/ether 52:54:00:76:6f:f0 brd ff:ff:ff:ff:ff:f
Alternatively, issue a command to open the team as follows: 
~]$ nmcli connection up Team0
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/4)
See Section 3.3, “Configuring IP Networking with nmcli” for an introduction to nmcli

8.10.2. Creating a Network Team Using teamd

Note

Configurations created using teamd are not persistent, and as such it may be necessary to create a team using the steps defined in Section 8.10.1, “Configure Network Teaming Using nmcli” or Section 8.10.3, “Creating a Network Team Using ifcfg Files”.
To create a network team, a JSON format configuration file is required for the virtual interface that will serve as the interface to the team of ports or links. A quick way is to copy the example configuration files and then edit them using an editor running with root privileges. To list the available example configurations, enter the following command: 
~]$ ls /usr/share/doc/teamd-*/example_configs/
activebackup_arp_ping_1.conf  activebackup_multi_lw_1.conf   loadbalance_2.conf
activebackup_arp_ping_2.conf  activebackup_nsna_ping_1.conf  loadbalance_3.conf
activebackup_ethtool_1.conf   broadcast.conf                 random.conf
activebackup_ethtool_2.conf   lacp_1.conf                    roundrobin_2.conf
activebackup_ethtool_3.conf   loadbalance_1.conf             roundrobin.conf
To view one of the included files, such as activebackup_ethtool_1.conf, enter the following command: 
~]$ cat /usr/share/doc/teamd-*/example_configs/activebackup_ethtool_1.conf
{
	"device":	"team0",
	"runner":	{"name": "activebackup"},
	"link_watch":	{"name": "ethtool"},
	"ports":	{
		"enp1s0": {
			"prio": -10,
			"sticky": true
		},
		"enp2s0": {
			"prio": 100
		}
	}
}
Create a working configurations directory to store teamd configuration files. For example, as normal user, enter a command with the following format: 
~]$ mkdir ~/teamd_working_configs
Copy the file you have chosen to your working directory and edit it as necessary. As an example, you could use a command with the following format: 
~]$ cp /usr/share/doc/teamd-*/example_configs/activebackup_ethtool_1.conf \ ~/teamd_working_configs/activebackup_ethtool_1.conf
To edit the file to suit your environment, for example to change the interfaces to be used as ports for the network team, open the file for editing as follows: 
~]$ vi ~/teamd_working_configs/activebackup_ethtool_1.conf
Make any necessary changes and save the file. See the vi(1) man page for help on using the vi editor or use your preferred editor.
Note that it is essential that the interfaces to be used as ports within the team must not be active, that is to say, they must be “down”, when adding them into a team device. To check their status, issue the following command: 
~]$ ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: em1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
    link/ether 52:54:00:d5:f7:d4 brd ff:ff:ff:ff:ff:ff
3: em2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
  link/ether 52:54:00:d8:04:70 brd ff:ff:ff:ff:ff:ff
In this example we see that both the interfaces we plan to use are “UP”.
To take down an interface, issue a command as root in the following format: 
~]# ip link set down em1
Repeat for each interface as necessary.
To create a team interface based on the configuration file, as root user, change to the working configurations directory (teamd_working_configs in this example): 
~]# cd /home/userteamd_working_configs
Then issue a command in the following format: 
~]# teamd -g -f activebackup_ethtool_1.conf -d
Using team device "team0".
Using PID file "/var/run/teamd/team0.pid"
Using config file "/home/user/teamd_working_configs/activebackup_ethtool_1.conf"
The -g option is for debug messages, -f option is to specify the configuration file to load, and the -d option is to make the process run as a daemon after startup. See the teamd(8) man page for other options.
To check the status of the team, issue the following command as root: 
~]# teamdctl team0 state
setup:
  runner: activebackup
ports:
  em1
    link watches:
      link summary: up
      instance[link_watch_0]:
        name: ethtool
        link: up
  em2
    link watches:
      link summary: up
      instance[link_watch_0]:
        name: ethtool
        link: up
runner:
  active port: em1
To apply an address to the network team interface, team0, issue a command as root in the following format: 
~]# ip addr add 192.168.23.2/24 dev team0
To check the IP address of a team interface, issue a command as follows: 
~]$ ip addr show team0
4: team0:  <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP
    link/ether 16:38:57:60:20:6f brd ff:ff:ff:ff:ff:ff
    inet 192.168.23.2/24 scope global team0
       valid_lft forever preferred_lft forever
    inet6 2620:52:0:221d:1438:57ff:fe60:206f/64 scope global dynamic
       valid_lft 2591880sec preferred_lft 604680sec
    inet6 fe80::1438:57ff:fe60:206f/64 scope link
       valid_lft forever preferred_lft forever
To activate the team interface, or to bring it “up”, issue a command as root in the following format: 
~]# ip link set dev team0 up
To temporarily deactivate the team interface, or to take it “down”, issue a command as root in the following format: 
~]# ip link set dev team0 down
To terminate, or kill, an instance of the team daemon, as root user, issue a command in the following format: 
~]# teamd -t team0 -k
The -k option is to specify that the instance of the daemon associated with the device team0 is to be killed. See the teamd(8) man page for other options.
For help on command-line options for teamd, issue the following command: 
~]$ teamd -h
In addition, see the teamd(8) man page.

8.10.3. Creating a Network Team Using ifcfg Files

To create a networking team using ifcfg files, create a file in the /etc/sysconfig/network-scripts/ directory as follows: 
DEVICE=team0
DEVICETYPE=Team
ONBOOT=yes
BOOTPROTO=none
IPADDR=192.168.11.1
PREFIX=24
TEAM_CONFIG='{"runner": {"name": "activebackup"}, "link_watch": {"name": "ethtool"}}'
This creates the interface to the team, in other words, this is the master.
To create a port to be a member of team0, create one or more files in the /etc/sysconfig/network-scripts/ directory as follows: 
DEVICE=enp1s0
HWADDR=D4:85:64:01:46:9E
DEVICETYPE=TeamPort
ONBOOT=yes
TEAM_MASTER=team0
TEAM_PORT_CONFIG='{"prio": 100}'
Add additional port interfaces similar to the above as required, changing the DEVICE and HWADDR field to match the ports (the network devices) being added. If port priority is not specified by prio it defaults to 0; it accepts negative and positive values in the range -32,767 to +32,767.
Specifying the hardware or MAC address using the HWADDR directive will influence the device naming procedure. This is explained in Chapter 11, Consistent Network Device Naming.
To open the network team, issue the following command as root: 
~]# ifup team0
To view the network team, issue the following command: 
~]$ ip link show

8.10.4. Add a Port to a Network Team Using iputils

To add a port em1 to a network team team0, using the ip utility, issue the following commands as root: 
~]# ip link set dev em1 down
~]# ip link set dev em1 master team0
Add additional ports as required. Team driver will bring ports up automatically.

8.10.5. Listing the ports of a Team Using teamnl

To view or list the ports in a network team, using the teamnl utility, issue the following command as root: 
~]# teamnl team0 ports
em2: up 100 fullduplex
em1: up 100 fullduplex

8.10.6. Configuring Options of a Team Using teamnl

To view or list all currently available options, using the teamnl utility, issue the following command as root: 
~]# teamnl team0 options
To configure a team to use active backup mode, issue the following command as root: 
~]# teamnl team0 setoption mode activebackup

8.10.7. Add an Address to a Network Team Using iputils

To add an address to a team team0, using the ip utility, issue the following command as root: 
~]# ip addr add 192.168.252.2/24 dev team0

8.10.8. open an Interface to a Network Team Using iputils

To activate or “open” an interface to a network team, team0, using the ip utility, issue the following command as root: 
~]# ip link set team0 up

8.10.9. Viewing the Active Port Options of a Team Using teamnl

To view or list the activeport option in a network team, using the teamnl utility, issue the following command as root: 
~]# teamnl team0 getoption activeport
0

8.10.10. Setting the Active Port Options of a Team Using teamnl

To set the activeport option in a network team, using the teamnl utility, issue the following command as root: 
~]# teamnl team0 setoption activeport 5
To check the change in team port options, issue the following command as root: 
~]# teamnl team0 getoption activeport
5

8.11. Controlling teamd with teamdctl

In order to query a running instance of teamd for statistics or configuration information, or to make changes, the control tool teamdctl is used.
To view the current team state of a team team0, enter the following command as root: 
~]# teamdctl team0 state view
For a more verbose output: 
~]# teamdctl team0 state view -v
For a complete state dump in JSON format (useful for machine processing) of team0, use the following command: 
~]# teamdctl team0 state dump
For a configuration dump in JSON format of team0, use the following command: 
~]# teamdctl team0 config dump
To view the configuration of a port em1, that is part of a team team0, enter the following command: 
~]# teamdctl team0 port config dump em1

8.11.1. Add a Port to a Network Team

To add a port em1 to a network team team0, issue the following command as root: 
~]# teamdctl team0 port add em1

Important

If using teamdctl directly to add a port, the port must be set to down. Otherwise the teamdctl team0 port add em1 command will fail.

8.11.2. Remove a Port From a Network Team

To remove an interface em1 from a network team team0, issue the following command as root: 
~]# teamdctl team0 port remove em1

8.11.3. Applying a Sticky Setting to a Port in a Network Team

You can use the teamdctl command to apply a sticky setting to ensure that a specific port is used as an active link when it is available.
Prerequisites
  • You already created a team of network interfaces. As a result, you have a port (em1) that you want to update the configuration of.
Procedure
To apply a JSON format configuration to a port em1 in a network team team0, run the following commands:
  1. Update the configuration of the sticky setting for em1: 
    ~]# teamdctl team0 port config update em1 '{ "prio": 100, "sticky": true }'
  2. Remove em1: 
    ~]# teamdctl team0 port remove em1
  3. Add em1 again so that the sticky setting takes effect: 
    ~]# teamdctl team0 port add em1
    Note that the old configuration will be overwritten and that any options omitted will be reset to the default values. See the teamdctl(8) man page for more team daemon control tool command examples.

8.11.4. View the Configuration of a Port in a Network Team

To copy the configuration of a port em1 in a network team team0, issue the following command as root: 
~]# teamdctl team0 port config dump em1
This will dump the JSON format configuration of the port to standard output.

8.12. Verifying Network Configuration Teaming for Redundancy

Network redundancy is a process when devices are used for backup purposes to prevent or recover from a failure of a specific system. The following procedure describes how to verify the network configuration for teaming in redundancy:
Procedure
  1. Ping the destination IP from the team interface. For example: 
    ~]# ping -I team0 DSTADDR
  2. View which interface is in active mode: 
    ~]# teamdctl team0 state
setup:
  runner: activebackup
ports:
  enp1s0
    link watches:
      link summary: up
      instance[link_watch_0]:
        name: ethtool
        link: up
        down count: 0
  enp2s0
    link watches:
      link summary: up
      instance[link_watch_0]:
        name: ethtool
        link: up
        down count: 0
runner:
  active port: enp1s0
    enp1s0 is the active interface.
  3. Temporarily remove the network cable from the host.

    Note

    There is no method to properly test link failure events using software utilities. Tools that deactivate connections, such as ip or nmcli, show only the driver’s ability to handle port configuration changes and not actual link failure events.
  4. Check if the backup interface is up: 
    ~]# teamdctl team0 state
setup:
 runner: activebackup
ports:
 enp1s0
   link watches:
     link summary: down
     instance[link_watch_0]:
       name: ethtool
       link: down
       down count: 1
 enp2s0
   link watches:
     link summary: up
     instance[link_watch_0]:
       name: ethtool
       link: up
       down count: 0
runner:
 active port: enp2s0
    enp2s0 is now the active interface.
  5. Check if you can still ping the destination IP from the team interface: 
    ~]# ping -I team0 DSTADDR

8.13. Configure teamd Runners

Runners are units of code which are compiled into the Team daemon when an instance of the daemon is created. For an introduction to the teamd runners, see Section 8.4, “Understanding the Network Teaming Daemon and the "Runners"”.

8.13.1. Configure the broadcast Runner

To configure the broadcast runner, using an editor as root, add the following to the team JSON format configuration file: 
{
 "device": "team0",
 "runner": {"name": "broadcast"},
 "ports": {"em1": {}, "em2": {}}
}
Please see the teamd.conf(5) man page for more information.

8.13.2. Configure the random Runner

The random runner behaves similarly to the round-robin runner.
To configure the random runner, using an editor as root, add the following to the team JSON format configuration file: 
{
 "device": "team0",
 "runner": {"name": "random"},
 "ports": {"em1": {}, "em2": {}}
}
Please see the teamd.conf(5) man page for more information.

8.13.3. Configure the Round-robin Runner

To configure the round-robin runner, using an editor as root, add the following to the team JSON format configuration file: 
{
 "device": "team0",
 "runner": {"name": "roundrobin"},
 "ports": {"em1": {}, "em2": {}}
}
A very basic configuration for round-robin.
Please see the teamd.conf(5) man page for more information.

8.13.4. Configure the activebackup Runner

The active backup runner can use all of the link-watchers to determine the status of links in a team. Any one of the following examples can be added to the team JSON format configuration file: 
{
   "device": "team0",
   "runner": {
      "name": "activebackup"
   },
   "link_watch": {
      "name": "ethtool"
   },
   "ports": {
      "em1": {
         "prio": -10,
         "sticky": true
      },
      "em2": {
         "prio": 100
      }
   }
}
This example configuration uses the active-backup runner with ethtool as the link watcher. Port em2 has higher priority. The sticky flag ensures that if em1 becomes active, it stays active as long as the link remains up. 
{
   "device": "team0",
   "runner": {
      "name": "activebackup"
   },
   "link_watch": {
      "name": "ethtool"
   },
   "ports": {
      "em1": {
         "prio": -10,
         "sticky": true,
         "queue_id": 4
      },
      "em2": {
         "prio": 100
      }
   }
}
This example configuration adds a queue ID of 4. It uses active-backup runner with ethtool as the link watcher. Port em2 has higher priority. But the sticky flag ensures that if em1 becomes active, it will stay active as long as the link remains up.
To configure the activebackup runner using ethtool as the link watcher and applying a delay, using an editor as root, add the following to the team JSON format configuration file: 
{
   "device": "team0",
   "runner": {
      "name": "activebackup"
   },
   "link_watch": {
      "name": "ethtool",
      "delay_up": 2500,
      "delay_down": 1000
   },
   "ports": {
      "em1": {
         "prio": -10,
         "sticky": true
      },
      "em2": {
         "prio": 100
      }
   }
}
This example configuration uses the active-backup runner with ethtool as the link watcher. Port em2 has higher priority. But the sticky flag ensures that if em1 becomes active, it stays active while the link remains up. Link changes are not propagated to the runner immediately, but delays are applied.
Please see the teamd.conf(5) man page for more information.

8.13.5. Configure the loadbalance Runner

This runner can be used for two types of load balancing, active and passive. In active mode, constant re-balancing of traffic is done by using statistics of recent traffic to share out traffic as evenly as possible. In passive mode, streams of traffic are distributed randomly across the available links. This has a speed advantage due to lower processing overhead. In high volume traffic applications this is often preferred as traffic usually consists of multiple stream which will be distributed randomly between the available links, in this way load sharing is accomplished without intervention by teamd.
To configure the loadbalance runner for passive transmit (Tx) load balancing, using an editor as root, add the following to the team JSON format configuration file: 
{
 "device": "team0",
 "runner": {
   "name": "loadbalance",
   "tx_hash": ["eth", "ipv4", "ipv6"]
 },
 "ports": {"em1": {}, "em2": {}}
}
Configuration for hash-based passive transmit (Tx) load balancing.
To configure the loadbalance runner for active transmit (Tx) load balancing, using an editor as root, add the following to the team JSON format configuration file: 
{
   "device": "team0",
   "runner": {
     "name": "loadbalance",
     "tx_hash": ["eth", "ipv4", "ipv6"],
     "tx_balancer": {
       "name": "basic"
     }
   },
   "ports": {"em1": {}, "em2": {}}
}
Configuration for active transmit (Tx) load balancing using basic load balancer.
Please see the teamd.conf(5) man page for more information.

8.13.6. Configure the LACP (802.3ad) Runner

To configure the LACP runner using ethtool as a link watcher, using an editor as root, add the following to the team JSON format configuration file: 
{
   "device": "team0",
   "runner": {
       "name": "lacp",
       "active": true,
       "fast_rate": true,
       "tx_hash": ["eth", "ipv4", "ipv6"]
   },
     "link_watch": {"name": "ethtool"},
     "ports": {"em1": {}, "em2": {}}
}
Configuration for connection to a link aggregation control protocol (LACP) capable counterpart. The LACP runner should use ethtool to monitor the status of a link. Note that only ethtool can be used for link monitoring because, for example in the case of arp_ping, the link would never come up. The reason is that the link has to be established first and only after that can packets, ARP included, go through. Using ethtool prevents this because it monitors each link layer individually.
Active load balancing is possible with this runner in the same way as it is done for the loadbalance runner. To enable active transmit (Tx) load balancing, add the following section: 
"tx_balancer": {
       "name": "basic"
}
Please see the teamd.conf(5) man page for more information.

8.13.8. Configure Port Selection Override

The physical port which transmits a frame is normally selected by the kernel part of the team driver, and is not relevant to the user or system administrator. The output port is selected using the policies of the selected team mode (teamd runner). On occasion however, it is helpful to direct certain classes of outgoing traffic to certain physical interfaces to implement slightly more complex policies. By default the team driver is multiqueue aware and 16 queues are created when the driver initializes. If more or less queues are required, the Netlink attribute tx_queues can be used to change this value during the team driver instance creation.
The queue ID for a port can be set by the port configuration option queue_id as follows: 
{
  "queue_id": 3
}
These queue ID's can be used in conjunction with the tc utility to configure a multiqueue queue discipline and filters to bias certain traffic to be transmitted on certain port devices. For example, if using the above configuration and wanting to force all traffic bound to 192.168.1.100 to use enp1s0 in the team as its output device, issue commands as root in the following format: 
~]# tc qdisc add dev team0 handle 1 root multiq
~]# tc filter add dev team0 protocol ip parent 1: prio 1 u32 match ip dst \
  192.168.1.100 action skbedit queue_mapping 3
This mechanism of overriding runner selection logic in order to bind traffic to a specific port can be used with all runners.

8.13.9. Configure BPF-based Tx Port Selectors

The loadbalance and LACP runners uses hashes of packets to sort network traffic flow. The hash computation mechanism is based on the Berkeley Packet Filter (BPF) code. The BPF code is used to generate a hash rather than make a policy decision for outgoing packets. The hash length is 8 bits giving 256 variants. This means many different socket buffers (SKB) can have the same hash and therefore pass traffic over the same link. The use of a short hash is a quick way to sort traffic into different streams for the purposes of load balancing across multiple links. In static mode, the hash is only used to decide out of which port the traffic should be sent. In active mode, the runner will continually reassign hashes to different ports in an attempt to reach a perfect balance.
The following fragment types or strings can be used for packet Tx hash computation:
  • eth — Uses source and destination MAC addresses.
  • vlan — Uses VLAN ID.
  • ipv4 — Uses source and destination IPv4 addresses.
  • ipv6 — Uses source and destination IPv6 addresses.
  • ip — Uses source and destination IPv4 and IPv6 addresses.
  • l3 — Uses source and destination IPv4 and IPv6 addresses.
  • tcp — Uses source and destination TCP ports.
  • udp — Uses source and destination UDP ports.
  • sctp — Uses source and destination SCTP ports.
  • l4 — Uses source and destination TCP and UDP and SCTP ports.
These strings can be used by adding a line in the following format to the load balance runner: 
"tx_hash": ["eth", "ipv4", "ipv6"]
See Section 8.13.5, “Configure the loadbalance Runner” for an example.

8.14. Creating a Network Team Using a GUI

8.14.1. Establishing a Team Connection

You can use nm-connection-editor to direct NetworkManager to create a team from two or more Wired or InfiniBand connections. It is not necessary to create the connections to be teamed first. They can be configured as part of the process to configure the team. You must have the MAC addresses of the interfaces available in order to complete the configuration process.

Procedure 8.1. Adding a New Team Connection Using nm-connection-editor

Follow the below steps to add a new team connection.
  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
  2. Click the Add button. The Choose a Connection Type window appears. Select Team and click Create. The Editing Team connection 1 window appears.
    The NetworkManager Graphical User Interface Add a menu

    Figure 8.6. The NetworkManager Graphical User Interface Add a menu

  3. On the Team tab, click Add and select the type of interface you want to use with the team connection. Click the Create button. Note that the dialog to select the port type only comes up when you create the first port; after that, it will automatically use that same type for all further ports.
  4. The Editing team0 slave 1 window appears.
    The NetworkManager Graphical User Interface Add a Slave Connection

    Figure 8.7. The NetworkManager Graphical User Interface Add a Slave Connection

  5. If custom port settings are to be applied, click on the Team Port tab and enter a JSON configuration string or import it from a file.
  6. Click the Save button.
  7. The name of the teamed port appears in the Teamed connections window. Click the Add button to add further port connections.
  8. Review and confirm the settings and then click the Save button.
  9. Edit the team-specific settings by referring to Section 8.14.1.1, “Configuring the Team Tab” below.

Procedure 8.2. Editing an Existing Team Connection

Follow the below steps to edit an existing team connection.
  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
  2. Select the connection you want to edit and click the Edit button.
  3. Select the General tab.
  4. Five settings in the Editing dialog are common to the most connection types. See the General tab:
    • Connection name — Enter a descriptive name for your network connection. This name is used to list this connection in the menu of the Network window.
    • Connection priority for auto-activation — If the connection is set to autoconnect, the number is activated (0 by default). The higher number means higher priority.
    • Automatically connect to this network when it is available — Select this box if you want NetworkManager to auto-connect to this connection when it is available. See the section called “Editing an Existing Connection with control-center” for more information.
    • All users may connect to this network — Select this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 3.4.5, “Managing System-wide and Private Connection Profiles with a GUI” for details.
    • Automatically connect to VPN when using this connection — Select this box if you want NetworkManager to auto-connect to a VPN connection when it is available. Select the VPN from the drop-down menu.
    • Firewall Zone — Select the firewall zone from the drop-down menu. See the Red Hat Enterprise Linux 7 Security Guide for more information on firewall zones.
  5. Edit the team-specific settings by referring to Section 8.14.1.1, “Configuring the Team Tab” below.
Saving Your New (or Modified) Connection and Making Further Configurations
Once you have finished editing your team connection, click the Save button to save your customized configuration.
Then, to configure:
8.14.1.1. Configuring the Team Tab
If you have already added a new team connection you can enter a custom JSON configuration string in the text box or import a configuration file. Click Save to apply the JSON configuration to the team interface.
For examples of JSON strings, see Section 8.13, “Configure teamd Runners”
See Procedure 8.1, “Adding a New Team Connection Using nm-connection-editor” for instructions on how to add a new team.

8.15. Additional Resources

Installed Documentation

  • teamd(8) man page — Describes the teamd service.
  • teamdctl(8) man page — Describes the teamd control tool.
  • teamd.conf(5) man page — Describes the teamd configuration file.
  • teamnl(8) man page — Describes the teamd Netlink library.
  • bond2team(1) man page — Describes a tool to convert bonding options to team.

Online Documentation

http://www.w3schools.com/js/js_json_syntax.asp
An explanation of JSON syntax.

Chapter 9. Configure Network Bridging

A network bridge is a link-layer device which forwards traffic between networks based on MAC addresses. It makes forwarding decisions based on a table of MAC addresses which it builds by listening to network traffic and thereby learning what hosts are connected to each network. A software bridge can be used within a Linux host in order to emulate a hardware bridge, for example in virtualization applications for sharing a NIC with one or more virtual NICs.
Note that a bridge cannot be established over Wi-Fi networks operating in Ad-Hoc or Infrastructure modes. This is due to the IEEE 802.11 standard that specifies the use of 3-address frames in Wi-Fi for the efficient use of airtime.

9.1. Configure Bridging Using the Text User Interface, nmtui

The text user interface tool nmtui can be used to configure bridging in a terminal window. Issue the following command to start the tool: 
~]$ nmtui
The text user interface appears. Any invalid command prints a usage message.
To navigate, use the arrow keys or press Tab to step forwards and press Shift+Tab to step back through the options. Press Enter to select an option. The Space bar toggles the status of a check box.
  1. From the starting menu, select Edit a connection. Select Add, the New Connection screen opens.
    The NetworkManager Text User Interface Add a Bridge Connection menu

    Figure 9.1. The NetworkManager Text User Interface Add a Bridge Connection menu

  2. Select Bridge, the Edit connection screen opens.
  3. To add port interfaces to the bridge select Add, the New Connection screen opens. Once the type of Connection has been chosen select the Create button to cause the bridge's Edit Connection display to appear.
    The NetworkManager Text User Interface Adding a new Bridge Slave Connection menu

    Figure 9.2. The NetworkManager Text User Interface Adding a new Bridge Slave Connection menu

  4. Enter the required port's device name or MAC address in the Device section. If required, enter a clone MAC address to be used as the bridge's MAC address by selecting Show to the right of the Ethernet label. Select the OK button.

    Note

    If the device is specified without a MAC address the Device section will be automatically populated once the Edit Connection window is reloaded, but only if it successfully finds the device.
    The NetworkManager Text User Interface Configuring a Bridge Slave Connection menu

    Figure 9.3. The NetworkManager Text User Interface Configuring a Bridge Slave Connection menu

  5. The name of the bridge port appears in the Slaves section. Repeat the above steps to add further port connections.
  6. Review and confirm the settings before selecting the OK button.
    The NetworkManager Text User Interface Configuring a Bridge menu

    Figure 9.4. The NetworkManager Text User Interface Configuring a Bridge menu

See Section 9.4.1.1, “Configuring the Bridge Tab” for definitions of the bridge terms.
See Section 3.2, “Configuring IP Networking with nmtui” for information on installing nmtui.

9.2. Using the NetworkManager Command Line Tool, nmcli

To create a bridge, named bridge-br0, issue a command as follows as root: 
~]# nmcli con add type bridge ifname br0
Connection 'bridge-br0' (6ad5bba6-98a0-4f20-839d-c997ba7668ad) successfully added.
If no interface name is specified, the name will default to bridge, bridge-1, bridge-2, and so on.
To view the connections, issue the following command: 
~]$ nmcli con show
NAME        UUID                                  TYPE            DEVICE
bridge-br0  79cf6a3e-0310-4a78-b759-bda1cc3eef8d  bridge          br0
enp1s0      4d5c449a-a6c5-451c-8206-3c9a4ec88bca  802-3-ethernet  enp1s0
Spanning tree protocol (STP) is enabled by default. The values used are from the IEEE 802.1D-1998 standard. To disable STP for this bridge, issue a command as follows as root: 
~]# nmcli con modify bridge-br0 bridge.stp no
To re-enable 802.1D STP for this bridge, issue a command as follows as root: 
~]# nmcli con modify bridge-br0 bridge.stp yes
The default bridge priority for 802.1D STP is 32768. The lower number is preferred in root bridge selection. For example, a bridge with priority of 28672 would be selected as the root bridge in preference to a bridge with priority value of 32768 (the default). To create a bridge with a non-default value, issue a command as follows: 
~]$ nmcli con add type bridge ifname br5 stp yes priority 28672
Connection 'bridge-br5' (86b83ad3-b466-4795-aeb6-4a66eb1856c7) successfully added.
The allowed values are in the range 0 to 65535.
To change the bridge priority of an existing bridge to a non-default value, issue a command in the following format: 
~]$ nmcli connection modify bridge-br5 bridge.priority 36864
The allowed values are in the range 0 to 65535.
To configure a bridge connection to forward group addresses in the range from 01:80:C2:00:00:00 to 01:80:C2:00:00:0F, change the group-forward-mask property. This property is a mask of 16 bits. Each bit corresponds to a group address in the above-mentioned range that must be forwarded. For example: 
~]$ nmcli connection modify bridge-br5 bridge.group-forward-mask 8

Important

The group-forward-mask property cannot have any of the 0, 1, 2 bits set to 1 because those addresses are used for Spanning tree protocol (STP), Link Aggregation Control Protocol (LACP) and Ethernet MAC pause frames.
To view the bridge settings, issue the following command: 
~]$ nmcli -f bridge con show bridge-br0
Further options for 802.1D STP are listed in the bridge section of the nmcli(1) man page.
To add, or assign an interface, for example enp1s0, to the bridge bridge-br0, issue a command as follows: 
~]$ nmcli con add type ethernet ifname enp1s0 master bridge-br0
Connection 'bridge-slave-enp1s0' (70ffae80-7428-4d9c-8cbd-2e35de72476e) successfully added.
To assign an existing connection to a bridge, proceed as follows:
  1. Change its controller and port-type properties. For example to assign an existing VLAN connection named vlan100: 
    ~]$ nmcli connection modify vlan100 master bridge-br0 slave-type bridge
  2. Reactivate the connection to apply the changes: 
    ~]$ nmcli connection up vlan100
To change a value using interactive mode, issue the following command: 
~]$ nmcli connection edit bridge-br0
You will be placed at the nmcli prompt. 
nmcli> set bridge.priority 4096
nmcli> save
Connection 'bridge-br0' (79cf6a3e-0310-4a78-b759-bda1cc3eef8d) successfully saved.
nmcli> quit
See Section 3.3, “Configuring IP Networking with nmcli” for an introduction to nmcli.

9.3. Using the Command Line Interface (CLI)

9.3.1. Check if Bridging Kernel Module is Installed

In Red Hat Enterprise Linux 7, the bridging module is loaded by default. If necessary, you can make sure that the module is loaded by issuing the following command as root: 
~]# modprobe --first-time bridge
modprobe: ERROR: could not insert 'bridge': Module already in kernel
To display information about the module, issue the following command: 
~]$ modinfo bridge
See the modprobe(8) man page for more command options.

9.3.2. Create a Network Bridge

To create a network bridge, create a file in the /etc/sysconfig/network-scripts/ directory called ifcfg-brN, replacing N with the number for the interface, such as 0.
The contents of the file is similar to whatever type of interface is getting bridged to, such as an Ethernet interface. The differences in this example are as follows:
  • The DEVICE directive is given an interface name as its argument in the format brN, where N is replaced with the number of the interface.
  • The TYPE directive is given an argument Bridge. This directive determines the device type and the argument is case sensitive.
  • The bridge interface configuration file is given an IP address whereas the physical interface configuration file must only have a MAC address (see below).
  • An extra directive, DELAY=0, is added to prevent the bridge from waiting while it monitors traffic, learns where hosts are located, and builds a table of MAC addresses on which to base its filtering decisions. The default delay of 15 seconds is not needed if no routing loops are possible.

Example 9.1. Example ifcfg-br0 Interface Configuration File

The following is an example of a bridge interface configuration file using a static IP address: 
DEVICE=br0
TYPE=Bridge
IPADDR=192.168.1.1
PREFIX=24
BOOTPROTO=none
ONBOOT=yes
DELAY=0
To complete the bridge another interface is created, or an existing interface is modified, and pointed to the bridge interface.

Example 9.2. Example ifcfg-enp1s0 Interface Configuration File

The following is an example of an Ethernet interface configuration file pointing to a bridge interface. Configure your physical interface in /etc/sysconfig/network-scripts/ifcfg-device_name, where device_name is the name of the interface 
DEVICE=device_name
TYPE=Ethernet
HWADDR=AA:BB:CC:DD:EE:FF
BOOTPROTO=none
ONBOOT=yes
BRIDGE=br0
Optionally specify a name using the NAME directive. If no name is specified, the NetworkManager plug-in, ifcfg-rh, will create a name for the connection profile in the form “Type Interface”. In this example, this means the bridge will be named Bridge br0. Alternately, if NAME=bridge-br0 is added to the ifcfg-br0 file the connection profile will be named bridge-br0.

Note

For the DEVICE directive, almost any interface name could be used as it does not determine the device type. TYPE=Ethernet is not strictly required. If the TYPE directive is not set, the device is treated as an Ethernet device (unless its name explicitly matches a different interface configuration file).
The directives are case sensitive.
Specifying the hardware or MAC address using the HWADDR directive will influence the device naming procedure as explained in Chapter 11, Consistent Network Device Naming.

Warning

If you are configuring bridging on a remote host, and you are connected to that host over the physical NIC you are configuring, consider the implications of losing connectivity before proceeding. You will lose connectivity when restarting the service and may not be able to regain connectivity if any errors have been made. Console, or out-of-band access is advised.
To open the new or recently configured interfaces, issue a command as root in the following format: 
ifup device
This command will detect if NetworkManager is running and call nmcli con load UUID and then call nmcli con up UUID.
Alternatively, to reload all interfaces, issue the following command as root: 
~]# systemctl restart network
This command will stop the network service, start the network service, and then call ifup for all ifcfg files with ONBOOT=yes.

Note

The default behavior is for NetworkManager not to be aware of changes to ifcfg files and to continue using the old configuration data until the interface is next brought up. This is set by the monitor-connection-files option in the NetworkManager.conf file. See the NetworkManager.conf(5) manual page for more information.

9.3.3. Network Bridge with Bond

An example of a network bridge formed from two or more bonded Ethernet interfaces will now be given as this is another common application in a virtualization environment. If you are not very familiar with the configuration files for bonded interfaces, see Section 7.4.2, “Create a Channel Bonding Interface”
Create or edit two or more Ethernet interface configuration files, which are to be bonded, as follows: 
DEVICE=interface_name
TYPE=Ethernet
SLAVE=yes
MASTER=bond0
BOOTPROTO=none
HWADDR=AA:BB:CC:DD:EE:FF

Note

Using interface_name as the interface name is common practice but almost any name could be used.
Create or edit one interface configuration file, /etc/sysconfig/network-scripts/ifcfg-bond0, as follows: 
DEVICE=bond0
ONBOOT=yes
BONDING_OPTS='mode=1 miimon=100'
BRIDGE=brbond0
For further instructions and advice on configuring the bonding module and to view the list of bonding parameters, see Section 7.7, “Using Channel Bonding”.
Create or edit one interface configuration file, /etc/sysconfig/network-scripts/ifcfg-brbond0, as follows: 
DEVICE=brbond0
ONBOOT=yes
TYPE=Bridge
IPADDR=192.168.1.1
PREFIX=24
We now have two or more interface configuration files with the MASTER=bond0 directive. These point to the configuration file named /etc/sysconfig/network-scripts/ifcfg-bond0, which contains the DEVICE=bond0 directive. This ifcfg-bond0 in turn points to the /etc/sysconfig/network-scripts/ifcfg-brbond0 configuration file, which contains the IP address, and acts as an interface to the virtual networks inside the host.
To open the new or recently configured interfaces, issue a command as root in the following format: 
ifup device
This command will detect if NetworkManager is running and call nmcli con load UUID and then call nmcli con up UUID.
Alternatively, to reload all interfaces, issue the following command as root: 
~]# systemctl restart network
This command will stop the network service, start the network service, and then call ifup for all ifcfg files with ONBOOT=yes.

Note

The default behavior is for NetworkManager not to be aware of changes to ifcfg files and to continue using the old configuration data until the interface is next brought up. This is set by the monitor-connection-files option in the NetworkManager.conf file. See the NetworkManager.conf(5) manual page for more information.

9.4. Configure Network Bridging Using a GUI

When starting a bridge interface, NetworkManager waits for at least one port to enter the “forwarding” state before beginning any network-dependent IP configuration such as DHCP or IPv6 autoconfiguration. Static IP addressing is allowed to proceed before any ports or ports are connected or begin forwarding packets.

9.4.1. Establishing a Bridge Connection with a GUI

Procedure 9.1. Adding a New Bridge Connection Using nm-connection-editor

Follow the below instructions to create a new bridge connection:
  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
  2. Click the Add button. The Choose a Connection Type window appears. Select Bridge and click Create. The Editing Bridge connection 1 window appears.
    Editing Bridge Connection 1

    Figure 9.5. Editing Bridge Connection 1

  3. Add port devices by referring to Procedure 9.3, “Adding a Port Interface to a Bridge” below.

Procedure 9.2. Editing an Existing Bridge Connection

  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
  2. Select the Bridge connection you want to edit.
  3. Click the Edit button.
Configuring the Connection Name, Auto-Connect Behavior, and Availability Settings
Five settings in the Editing dialog are common to all connection types, see the General tab:
  • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the menu of the Network window.
  • Automatically connect to this network when it is available — Select this box if you want NetworkManager to auto-connect to this connection when it is available. See the section called “Editing an Existing Connection with control-center” for more information.
  • All users may connect to this network — Select this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 3.4.5, “Managing System-wide and Private Connection Profiles with a GUI” for details.
  • Automatically connect to VPN when using this connection — Select this box if you want NetworkManager to auto-connect to a VPN connection when it is available. Select the VPN from the dropdown menu.
  • Firewall Zone — Select the Firewall Zone from the dropdown menu. See the Red Hat Enterprise Linux 7 Security Guide for more information on Firewall Zones.
9.4.1.1. Configuring the Bridge Tab
Interface name
The name of the interface to the bridge.
Bridged connections
One or more port interfaces.
Aging time
The time, in seconds, a MAC address is kept in the MAC address forwarding database.
Enable IGMP snooping
If required, select the check box to enable IGMP snooping on the device.
Enable STP (Spanning Tree Protocol)
If required, select the check box to enable STP.
Priority
The bridge priority; the bridge with the lowest priority will be elected as the root bridge.
Forward delay
The time, in seconds, spent in both the Listening and Learning states before entering the Forwarding state. The default is 15 seconds.
Hello time
The time interval, in seconds, between sending configuration information in bridge protocol data units (BPDU).
Max age
The maximum time, in seconds, to store the configuration information from BPDUs. This value should be twice the Hello Time plus 1 but less than twice the Forwarding delay minus 1.
Group forward mask
This property is a mask of group addresses that allows group addresses to be forwarded. In most cases, group addresses in the range from 01:80:C2:00:00:00 to 01:80:C2:00:00:0F are not forwarded by the bridge device. This property is a mask of 16 bits, each corresponding to a group address in the above range, that must be forwarded. Note that the Group forward mask property cannot have any of the 0, 1, 2 bits set to 1 because those addresses are used for Spanning tree protocol (STP), Link Aggregation Control Protocol (LACP) and Ethernet MAC pause frames.

Procedure 9.3. Adding a Port Interface to a Bridge

  1. To add a port to a bridge, select the Bridge tab in the Editing Bridge connection 1 window. If necessary, open this window by following the procedure in Procedure 9.2, “Editing an Existing Bridge Connection”.
  2. Click Add. The Choose a Connection Type menu appears.
  3. Select the type of connection to be created from the list. Click Create. A window appropriate to the connection type selected appears.
    The NetworkManager Graphical User Interface Add a Bridge Connection

    Figure 9.6. The NetworkManager Graphical User Interface Add a Bridge Connection

  4. Select the Bridge Port tab. Configure Priority and Path cost as required. Note the STP priority for a bridge port is limited by the Linux kernel. Although the standard allows a range of 0 to 255, Linux only allows 0 to 63. The default is 32 in this case.
    The NetworkManager Graphical User Interface Bridge Port tab

    Figure 9.7. The NetworkManager Graphical User Interface Bridge Port tab

  5. If required, select the Hairpin mode check box to enable forwarding of frames for external processing. Also known as virtual Ethernet port aggregator (VEPA) mode.
Then, to configure:
Saving Your New (or Modified) Connection and Making Further Configurations
Once you have finished editing your new bridge connection, click the Save button to save your customized configuration. If the profile was in use while being edited, power cycle the connection to make NetworkManager apply the changes. If the profile is OFF, set it to ON or select it in the network connection icon's menu. See Section 3.4.1, “Connecting to a Network Using the control-center GUI” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network window and clicking Options to return to the Editing dialog.
Then, to configure:
Once saved the Bridge will appear in the Network settings tool with each port showing in the display.
The NetworkManager Graphical User Interface with Bridge

Figure 9.8. The NetworkManager Graphical User Interface with Bridge

9.5. Ethernet Bridge Configuration Using iproute

The iproute package can be used as an alternative to the bridge-utils. It allows to set bridge port options such as priority, cost or state.
To set port options for an interface enp1s0 assigned to a bridge device, using the ip utility, issue the following command as root: 
~]# ip link set enp1s0 type bridge_slave option
To select the available options, using the ip utility, issue the following command as root: 
~]# ip link help bridge_slave
      Usage: ... bridge_slave [ state STATE ] [ priority PRIO ] [cost COST ]
                          [ guard {on | off} ]
                          [ hairpin {on | off} ]
                          [ fastleave {on | off} ]
                          [ root_block {on | off} ]
                          [ learning {on | off} ]
                          [ flood {on | off} ]
For more details on the port options, see the ip-link(8) man page.

9.6. Additional Resources

  • nmcli(1) man page — Describes NetworkManager's command‐line tool.
  • nmcli-examples(5) man page — Gives examples of nmcli commands.
  • nm-settings(5) man page — Description of settings and parameters of NetworkManager connections.
  • ip-link(8) man page — Description of the bridge port options.

Chapter 10. Configure 802.1Q VLAN tagging

To create a VLAN, an interface is created on top of another interface referred to as the parent interface. The VLAN interface will tag packets with the VLAN ID as they pass through the interface, and returning packets will be untagged. VLAN interface can be configured similarly to any other interface. The parent interface does not need to be an Ethernet interface. An 802.1Q VLAN tagging interface can be created on top of bridge, bond, and team interfaces, however there are some things to note:
  • In the case of VLANs over bonds, it is important that the bond has ports and that they are “up” before opening the VLAN interface. Adding a VLAN interface to a bond without ports does not work.
  • A VLAN port cannot be configured on a bond with the fail_over_mac=follow option, because the VLAN virtual device cannot change its MAC address to match the parent's new MAC address. In such a case, traffic would still be sent with the now incorrect source MAC address.
  • Sending VLAN tagged packets through a network switch requires the switch to be properly configured. For example, ports on Cisco switches must be assigned to one VLAN or be configured as trunk ports to accept tagged packets from multiple VLANs. Some vendor switches allow untagged frames of the native VLAN to be processed by a trunk port. Some devices allow you to enable or disable the native VLAN, other devices have it disabled by default. Consequence of this disparity may result in native VLAN misconfiguration between two different switches, posing a security risk. For example:
    One switch uses native VLAN 1 while the other uses native VLAN 10. If the frames are allowed to pass without the tag being inserted, an attacker is able to jump VLANs - this common network penetration technique is also known as VLAN hopping.
    To minimize security risks, configure your interface as follows:
    Switches
    • Unless you need them, disable trunk ports.
    • If you need trunk ports, disable native VLAN, so that untagged frames are not allowed.
    Red Hat Enterprise Linux server
    • Use the nftables or ebtables utilities to drop untagged frames in ingress filtering.
  • Some older network interface cards, loopback interfaces, Wimax cards, and some InfiniBand devices, are said to be VLAN challenged, meaning they cannot support VLANs. This is usually because the devices cannot cope with VLAN headers and the larger MTU size associated with tagged packets.

Note

Bonding on top of VLAN is not supported by Red Hat. See the Red Hat Knowledgebase article Whether configuring bond on top of VLAN as port interfaces is a valid configuration? for more information.

10.1. Selecting VLAN Interface Configuration Methods

10.2. Configure 802.1Q VLAN tagging Using the Text User Interface, nmtui

The text user interface tool nmtui can be used to configure 802.1Q VLANs in a terminal window. Issue the following command to start the tool: 
~]$ nmtui
The text user interface appears. Any invalid command prints a usage message.
To navigate, use the arrow keys or press Tab to step forwards and press Shift+Tab to step back through the options. Press Enter to select an option. The Space bar toggles the status of a check box.
From the starting menu, select Edit a connection. Select Add, the New Connection screen opens.
The NetworkManager Text User Interface Add a VLAN Connection menu

Figure 10.1. The NetworkManager Text User Interface Add a VLAN Connection menu

Select VLAN, the Edit connection screen opens. Follow the on-screen prompts to complete the configuration.
The NetworkManager Text User Interface Configuring a VLAN Connection menu

Figure 10.2. The NetworkManager Text User Interface Configuring a VLAN Connection menu

See Section 10.5.1.1, “Configuring the VLAN Tab” for definitions of the VLAN terms.
See Section 3.2, “Configuring IP Networking with nmtui” for information on installing nmtui.

10.3. Configure 802.1Q VLAN Tagging Using the Command Line Tool, nmcli

To view the available interfaces on the system, issue a command as follows: 
~]$ nmcli con show
NAME         UUID                                  TYPE            DEVICE
System enp2s0  9c92fad9-6ecb-3e6c-eb4d-8a47c6f50c04  802-3-ethernet  enp2s0
System enp1s0  5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03  802-3-ethernet  enp1s0
Note that the NAME field in the output always denotes the connection ID. It is not the interface name even though it might look the same. The ID can be used in nmcli connection commands to identify a connection. Use the DEVICE name with other applications such as firewalld.
To create an 802.1Q VLAN interface on Ethernet interface enp1s0, with VLAN interface VLAN10 and ID 10, issue a command as follows: 
~]$ nmcli con add type vlan ifname VLAN10 dev enp1s0 id 10
Connection 'vlan-VLAN10' (37750b4a-8ef5-40e6-be9b-4fb21a4b6d17) successfully added.
Note that as no con-name was given for the VLAN interface, the name was derived from the interface name by prepending the type. Alternatively, specify a name with the con-name option as follows: 
~]$ nmcli con add type vlan con-name VLAN12 dev enp1s0 id 12
Connection 'VLAN12' (b796c16a-9f5f-441c-835c-f594d40e6533) successfully added.

Assigning Addresses to VLAN Interfaces

You can use the same nmcli commands to assign static and dynamic interface addresses as with any other interface.
For example, a command to create a VLAN interface with a static IPv4 address and gateway is as follows: 
~]$ nmcli con add type vlan con-name VLAN20 dev enp1s0 id 20 ip4 10.10.10.10/24 \
gw4 10.10.10.254
To create a VLAN interface with dynamically assigned addressing, issue a command as follows: 
~]$ nmcli con add type vlan con-name VLAN30 dev enp1s0 id 30
See Section 3.3.6, “Connecting to a Network Using nmcli” for examples of using nmcli commands to configure interfaces.
To review the VLAN interfaces created, issue a command as follows: 
~]$ nmcli con show
NAME         UUID                                  TYPE            DEVICE
VLAN12         4129a37d-4feb-4be5-ac17-14a193821755  vlan            enp1s0.12
System enp2s0  9c92fad9-6ecb-3e6c-eb4d-8a47c6f50c04  802-3-ethernet  enp2s0
System enp1s0  5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03  802-3-ethernet  enp1s0
vlan-VLAN10    1be91581-11c2-461a-b40d-893d42fed4f4  vlan            VLAN10
To view detailed information about the newly configured connection, issue a command as follows: 
~]$ nmcli -p con show VLAN12
===============================================================================
                      Connection profile details (VLAN12)
===============================================================================
connection.id:                          VLAN12
connection.uuid:                        4129a37d-4feb-4be5-ac17-14a193821755
connection.interface-name:              --
connection.type:                        vlan
connection.autoconnect:                 yes
…
-------------------------------------------------------------------------------
802-3-ethernet.port:                    --
802-3-ethernet.speed:                   0
802-3-ethernet.duplex:                  --
802-3-ethernet.auto-negotiate:          yes
802-3-ethernet.mac-address:             --
802-3-ethernet.cloned-mac-address:      --
802-3-ethernet.mac-address-blacklist:
802-3-ethernet.mtu:                     auto
…
vlan.interface-name:                    --
vlan.parent:                            enp1s0
vlan.id:                                12
vlan.flags:                             0 (NONE)
vlan.ingress-priority-map:
vlan.egress-priority-map:
-------------------------------------------------------------------------------
===============================================================================
      Activate connection details (4129a37d-4feb-4be5-ac17-14a193821755)
===============================================================================
GENERAL.NAME:                           VLAN12
GENERAL.UUID:                           4129a37d-4feb-4be5-ac17-14a193821755
GENERAL.DEVICES:                        enp1s0.12
GENERAL.STATE:                          activating
[output truncated]
Further options for the VLAN command are listed in the VLAN section of the nmcli(1) man page. In the man pages the device on which the VLAN is created is referred to as the parent device. In the example above the device was specified by its interface name, enp1s0, it can also be specified by the connection UUID or MAC address.
To create an 802.1Q VLAN connection profile with ingress priority mapping on Ethernet interface enp2s0, with name VLAN1 and ID 13, issue a command as follows: 
~]$ nmcli con add type vlan con-name VLAN1 dev enp2s0 id 13 ingress "2:3,3:5"
To view all the parameters associated with the VLAN created above, issue a command as follows: 
~]$ nmcli connection show vlan-VLAN10
To change the MTU, issue a command as follows: 
~]$ nmcli connection modify vlan-VLAN10 802.mtu 1496
The MTU setting determines the maximum size of the network layer packet. The maximum size of the payload the link-layer frame can carry in turn limits the network layer MTU. For standard Ethernet frames this means an MTU of 1500 bytes. It should not be necessary to change the MTU when setting up a VLAN as the link-layer header is increased in size by 4 bytes to accommodate the 802.1Q tag.
At time of writing, connection.interface-name and vlan.interface-name have to be the same (if they are set). They must therefore be changed simultaneously using nmcli's interactive mode. To change a VLAN connections name, issue commands as follows: 
~]$ nmcli con edit vlan-VLAN10
nmcli> set vlan.interface-name superVLAN
nmcli> set connection.interface-name superVLAN
nmcli> save
nmcli> quit
The nmcli utility can be used to set and clear ioctl flags which change the way the 802.1Q code functions. The following VLAN flags are supported by NetworkManager:
  • 0x01 - reordering of output packet headers
  • 0x02 - use GVRP protocol
  • 0x04 - loose binding of the interface and its master
The state of the VLAN is synchronized to the state of the parent or master interface (the interface or device on which the VLAN is created). If the parent interface is set to the “down” administrative state then all associated VLANs are set down and all routes are flushed from the routing table. Flag 0x04 enables a loose binding mode, in which only the operational state is passed from the parent to the associated VLANs, but the VLAN device state is not changed.
To set a VLAN flag, issue a command as follows: 
~]$ nmcli connection modify vlan-VLAN10 vlan.flags 1
See Section 3.3, “Configuring IP Networking with nmcli” for an introduction to nmcli.

10.4. Configure 802.1Q VLAN Tagging Using the Command Line

In Red Hat Enterprise Linux 7, the 8021q module is loaded by default. If necessary, you can make sure that the module is loaded by issuing the following command as root: 
~]# modprobe --first-time 8021q
modprobe: ERROR: could not insert '8021q': Module already in kernel
To display information about the module, issue the following command: 
~]$ modinfo 8021q
See the modprobe(8) man page for more command options.

10.4.1. Setting Up 802.1Q VLAN Tagging Using ifcfg Files

  1. Configure the parent interface in /etc/sysconfig/network-scripts/ifcfg-device_name, where device_name is the name of the interface: 
    DEVICE=interface_name
TYPE=Ethernet
BOOTPROTO=none
ONBOOT=yes
  2. Configure the VLAN interface configuration in the /etc/sysconfig/network-scripts/ directory. The configuration file name should be the parent interface plus a . character plus the VLAN ID number. For example, if the VLAN ID is 192, and the parent interface is enp1s0, then the configuration file name should be ifcfg-enp1s0.192: 
    DEVICE=enp1s0.192
BOOTPROTO=none
ONBOOT=yes
IPADDR=192.168.1.1
PREFIX=24
NETWORK=192.168.1.0
VLAN=yes
    If there is a need to configure a second VLAN, with for example, VLAN ID 193, on the same interface, enp1s0, add a new file with the name enp1s0.193 with the VLAN configuration details.
  3. Restart the networking service in order for the changes to take effect. As root issue the following command: 
    ~]# systemctl restart network

10.4.2. Configure 802.1Q VLAN Tagging Using ip Commands

To create an 802.1Q VLAN interface on Ethernet interface enp1s0, with name VLAN8 and ID 8, issue a command as root as follows: 
~]# ip link add link enp1s0 name enp1s0.8 type vlan id 8
To view the VLAN, issue the following command: 
~]$ ip -d link show enp1s0.8
4: enp1s0.8@enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT
     link/ether 52:54:00:ce:5f:6c brd ff:ff:ff:ff:ff:ff promiscuity 0
     vlan protocol 802.1Q id 8 <REORDER_HDR>
Note that the ip utility interprets the VLAN ID as a hexadecimal value if it is preceded by 0x and as an octal value if it has a leading 0. This means that in order to assign a VLAN ID with a decimal value of 22, you must not add any leading zeros.
To remove the VLAN, issue a command as root as follows: 
~]# ip link delete enp1s0.8
To use multiple interfaces belonging to multiple VLANs, create locally enp1s0.1 and enp1s0.2 with the appropriate VLAN ID on top of a physical interface enp1s0: 
~]# ip link add link enp1s0 name enp1s0.1 type vlan id 1
    ip link set dev enp1s0.1 up
~]# ip link add link enp1s0 name enp1s0.2 type vlan id 2
    ip link set dev enp1s0.2 up
Note that running a network sniffer on a physical device, you can capture the tagged frames reaching the physical device, even if no VLAN device is configured on top of enp1s0. For example: 
tcpdump -nnei enp1s0 -vvv

Note

VLAN interfaces created using ip commands at the command prompt will be lost if the system is shutdown or restarted. To configure VLAN interfaces to be persistent after a system restart, use ifcfg files. See Section 10.4.1, “Setting Up 802.1Q VLAN Tagging Using ifcfg Files”

10.5. Configure 802.1Q VLAN Tagging Using a GUI

10.5.1. Establishing a VLAN Connection

You can use nm-connection-editor to create a VLAN using an existing interface as the parent interface. Note that VLAN devices are only created automatically if the parent interface is set to connect automatically.

Procedure 10.1. Adding a New VLAN Connection Using nm-connection-editor

  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
  2. Click the Add button. The Choose a Connection Type window appears. Select VLAN and click Create. The Editing VLAN connection 1 window appears.
  3. On the VLAN tab, select the parent interface from the drop-down list you want to use for the VLAN connection.
  4. Enter the VLAN ID
  5. Enter a VLAN interface name. This is the name of the VLAN interface that will be created. For example, enp1s0.1 or vlan2. (Normally this is either the parent interface name plus “.” and the VLAN ID, or “vlan” plus the VLAN ID.)
  6. Review and confirm the settings and then click the Save button.
  7. To edit the VLAN-specific settings see Section 10.5.1.1, “Configuring the VLAN Tab”.
Adding a New VLAN Connection Using nm-connection-editor

Figure 10.3. Adding a New VLAN Connection Using nm-connection-editor

Procedure 10.2. Editing an Existing VLAN Connection

Follow these steps to edit an existing VLAN connection.
  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
  2. Select the connection you want to edit and click the Edit button.
  3. Select the General tab.
  4. Configure the connection name, auto-connect behavior, and availability settings.
    These settings in the Editing dialog are common to all connection types:
  5. To edit the VLAN-specific settings see Section 10.5.1.1, “Configuring the VLAN Tab”.
Saving Your New (or Modified) Connection and Making Further Configurations
Once you have finished editing your VLAN connection, click the Save button to save your customized configuration.
Then, to configure:
10.5.1.1. Configuring the VLAN Tab
If you have already added a new VLAN connection (see Procedure 10.1, “Adding a New VLAN Connection Using nm-connection-editor” for instructions), you can edit the VLAN tab to set the parent interface and the VLAN ID.
Parent Interface
A previously configured interface can be selected in the drop-down list.
VLAN ID
The identification number to be used to tag the VLAN network traffic.
VLAN interface name
The name of the VLAN interface that will be created. For example, enp1s0.1 or vlan2.
Cloned MAC address
Optionally sets an alternate MAC address to use for identifying the VLAN interface. This can be used to change the source MAC address for packets sent on this VLAN.
MTU
Optionally sets a Maximum Transmission Unit (MTU) size to be used for packets to be sent over the VLAN connection.

10.6. VLAN on Bond and Bridge Using ip Commands

To use VLANs over bonds and bridges, proceed as follows:
  1. Add a bond device as root: 
    # ip link add bond0 type bond
# ip link set bond0 type bond miimon 100 mode active-backup
# ip link set em1 down
# ip link set em1 master bond0
# ip link set em2 down
# ip link set em2 master bond0
# ip link set bond0 up
  2. Set VLAN on the bond device: 
    # ip link add link bond0 name bond0.2 type vlan id 2
# ip link set bond0.2 up
  3. Add the bridge device and attach VLAN to it: 
    # ip link add br0 type bridge
# ip link set bond0.2 master br0
# ip link set br0 up

10.7. VLAN on Bond and Bridge Using the NetworkManager Command Line Tool, nmcli

To use VLANs over bonds and bridges, proceed as follows:
  1. Add a bond device: 
    ~]$ nmcli connection add type bond con-name Bond0 ifname bond0 bond.options "mode=active-backup,miimon=100" ipv4.method disabled ipv6.method ignore
    Note that in this case a bond connection serves only as a "lower interface" for VLAN, and does not get any IP address. Therefore, the ipv4.method disabled and ipv6.method ignore parameters have been added on the command line.
  2. Add ports to the bond device: 
    ~]$ nmcli connection add type ethernet con-name Slave1 ifname em1 master bond0 slave-type bond
~]$ nmcli connection add type ethernet con-name Slave2 ifname em2 master bond0 slave-type bond
  3. Add a bridge device: 
    ~]$ nmcli connection add type bridge con-name Bridge0 ifname br0 ipv4.method manual ipv4.addresses 192.0.2.1/24
  4. Add a VLAN interface on top of bond, assigned to the bridge device: 
    ~]$ nmcli connection add type vlan con-name Vlan2 ifname bond0.2 dev bond0 id 2 master br0 slave-type bridge
  5. View the created connections: 
    ~]$ nmcli connection show
 NAME     UUID                                  TYPE            DEVICE
 Bond0    f05806fa-72c3-4803-8743-2377f0c10bed  bond            bond0
 Bridge0  22d3c0de-d79a-4779-80eb-10718c2bed61  bridge          br0
 Slave1   e59e13cb-d749-4df2-aee6-de3bfaec698c  802-3-ethernet  em1
 Slave2   25361a76-6b3c-4ae5-9073-005be5ab8b1c  802-3-ethernet  em2
 Vlan2    e2333426-eea4-4f5d-a589-336f032ec822  vlan            bond0.2

10.8. Configuring VLAN switchport mode

Red Hat Enterprise Linux machines are often used as routers and enable an advanced VLAN configuration on their network interfaces. You need to set switchport mode when the Ethernet interface is connected to a switch and there are VLANs running over the physical interface. A Red Hat Enterprise Linux server or workstation is usually connected to only one VLAN, which makes switchport mode access suitable, and the default setting.
In certain scenarios, multiple tagged VLANs use the same physical link, that is Ethernet between the switch and Red Hat Enterprise Linux machine, which requires switchport mode trunk to be configured on both ends.
For example, when a Red Hat Enterprise Linux machine is used as a router, the machine needs to forward tagged packets from the various VLANs behind the router to the switch over the same physical Ethernet, and maintain separation between those VLANs.
With the setup described, for example, in Section 10.3, “Configure 802.1Q VLAN Tagging Using the Command Line Tool, nmcli”, use the Cisco switchport mode trunk. If you only set an IP address on an interface, use Cisco switchport mode access.

10.9. Additional Resources

  • ip-link(8) man page — Describes the ip utility's network device configuration commands.
  • nmcli(1) man page — Describes NetworkManager's command‐line tool.
  • nmcli-examples(5) man page — Gives examples of nmcli commands.
  • nm-settings(5) man page — Description of settings and parameters of NetworkManager connections.
  • nm-settings-ifcfg-rh(5) man page — Description of ifcfg-rh settings in the /etc/sysconfig/network-scripts/ifcfg-* files.

Chapter 11. Consistent Network Device Naming

Red Hat Enterprise Linux provides methods for consistent and predictable network device naming for network interfaces. These features change the name of network interfaces on a system in order to make locating and differentiating the interfaces easier.
Traditionally, network interfaces in Linux are enumerated as eth[0123…]s0, but these names do not necessarily correspond to actual labels on the chassis. Modern server platforms with multiple network adapters can encounter non-deterministic and counter-intuitive naming of these interfaces. This affects both network adapters embedded on the motherboard (Lan-on-Motherboard, or LOM) and add-in (single and multiport) adapters.
In Red Hat Enterprise Linux, udev supports a number of different naming schemes. The default is to assign fixed names based on firmware, topology, and location information. This has the advantage that the names are fully automatic, fully predictable, that they stay fixed even if hardware is added or removed (no re-enumeration takes place), and that broken hardware can be replaced seamlessly. The disadvantage is that they are sometimes harder to read than the eth or wla names traditionally used. For example: enp5s0.

Warning

Red Hat does not support systems with consistent device naming disabled. For further details, see Is it safe to set net.ifnames=0?

11.1. Naming Schemes Hierarchy

By default, systemd will name interfaces using the following policy to apply the supported naming schemes:
  • Scheme 1: Names incorporating Firmware or BIOS provided index numbers for on-board devices (example: eno1), are applied if that information from the firmware or BIOS is applicable and available, else falling back to scheme 2.
  • Scheme 2: Names incorporating Firmware or BIOS provided PCI Express hotplug slot index numbers (example: ens1) are applied if that information from the firmware or BIOS is applicable and available, else falling back to scheme 3.
  • Scheme 3: Names incorporating physical location of the connector of the hardware (example: enp2s0), are applied if applicable, else falling directly back to scheme 5 in all other cases.
  • Scheme 4: Names incorporating interface's MAC address (example: enx78e7d1ea46da), is not used by default, but is available if the user chooses.
  • Scheme 5: The traditional unpredictable kernel naming scheme, is used if all other methods fail (example: eth0).
This policy, the procedure outlined above, is the default. If the system has biosdevname enabled, it will be used. Note that enabling biosdevname requires passing biosdevname=1 as a kernel command-line parameter, except in the case of a Dell system, where biosdevname will be used by default as long as it is installed. If the user has added udev rules which change the name of the kernel devices, those rules will take precedence.

11.2. Understanding the Device Renaming Procedure

The device name procedure in detail is as follows:
  1. A rule in /usr/lib/udev/rules.d/60-net.rules instructs the udev helper utility, /lib/udev/rename_device, to look into all /etc/sysconfig/network-scripts/ifcfg-suffix files. If it finds an ifcfg file with a HWADDR entry matching the MAC address of an interface it renames the interface to the name given in the ifcfg file by the DEVICE directive.
  2. A rule in /usr/lib/udev/rules.d/71-biosdevname.rules instructs biosdevname to rename the interface according to its naming policy, provided that it was not renamed in a previous step, biosdevname is installed, and biosdevname=0 was not given as a kernel command on the boot command line.
  3. A rule in /lib/udev/rules.d/75-net-description.rules instructs udev to fill in the internal udev device property values ID_NET_NAME_ONBOARD, ID_NET_NAME_SLOT, ID_NET_NAME_PATH, ID_NET_NAME_MAC by examining the network interface device. Note, that some device properties might be undefined.
  4. A rule in /usr/lib/udev/rules.d/80-net-name-slot.rules instructs udev to rename the interface, provided that it was not renamed in step 1 or 2, and the kernel parameter net.ifnames=0 was not given, according to the following priority: ID_NET_NAME_ONBOARD, ID_NET_NAME_SLOT, ID_NET_NAME_PATH. It falls through to the next in the list, if one is unset. If none of these are set, then the interface will not be renamed.
Steps 3 and 4 are implementing the naming schemes 1, 2, 3, and optionally 4, described in Section 11.1, “Naming Schemes Hierarchy”. Step 2 is explained in more detail in Section 11.6, “Consistent Network Device Naming Using biosdevname”.

11.3. Understanding the Predictable Network Interface Device Names

The names have two-character prefixes based on the type of interface:
  1. en for Ethernet,
  2. wl for wireless LAN (WLAN),
  3. ww for wireless wide area network (WWAN).
The names have the following types:
o<index>
on-board device index number
s<slot>[f<function>][d<dev_id>]
hotplug slot index number. All multi-function PCI devices will carry the [f<function>] number in the device name, including the function 0 device.
x<MAC>
MAC address
[P<domain>]p<bus>s<slot>[f<function>][d<dev_id>]
PCI geographical location. In PCI geographical location, the [P<domain>] number is only mentioned if the value is not 0. For example:
ID_NET_NAME_PATH=P1enp5s0
[P<domain>]p<bus>s<slot>[f<function>][u<port>][..][c<config>][i<interface>]
USB port number chain. For USB devices, the full chain of port numbers of hubs is composed. If the name gets longer than the maximum number of 15 characters, the name is not exported. If there are multiple USB devices in the chain, the default values for USB configuration descriptors (c1) and USB interface descriptors (i0) are suppressed.

11.4. Naming Scheme for Network Devices Available for Linux on System z

Use the bus-ID to create predictable device names for network interfaces in Linux on System z instances. The bus-ID identifies a device in the s390 channel subsystem. A bus ID identifies the device within the scope of a Linux instance. For a CCW device, the bus ID is the device's device number with a leading 0.n, where n is the subchannel set ID. For example, 0.1.0ab1.
Network interfaces of device type Ethernet are named as follows: 
enccw0.0.1234
CTC network devices of device type SLIP are named as follows: 
slccw0.0.1234
Use the znetconf -c command or the lscss -a command to display available network devices and their bus-IDs.
Table 11.1. Device Name Types for Linux on System z
FormatDescription
enccwbus-IDdevice type Ethernet
slccwbus-IDCTC network devices of device type SLIP

11.5. Naming Scheme for VLAN Interfaces

Traditionally, VLAN interface names in the format: interface-name.VLAN-ID are used. The VLAN-ID ranges from 0 to 4096, which is a maximum of four characters and the total interface name has a limit of 15 characters. The maximum interface name length is defined by the kernel headers and is a global limit, affecting all applications.
In Red Hat Enterprise Linux 7, four naming conventions for VLAN interface names are supported:
VLAN plus VLAN ID
The word vlan plus the VLAN ID. For example: vlan0005
VLAN plus VLAN ID without padding
The word vlan plus the VLAN ID without padding by means of additional leading zeros. For example: vlan5
Device name plus VLAN ID
The name of the parent interface plus the VLAN ID. For example: enp1s0.0005
Device name plus VLAN ID without padding
The name of the parent interface plus the VLAN ID without padding by means of additional leading zeros. For example: enp1s0.5

11.6. Consistent Network Device Naming Using biosdevname

This feature, implemented through the biosdevname udev helper utility, will change the name of all embedded network interfaces, PCI card network interfaces, and virtual function network interfaces from the existing eth[0123…] to the new naming convention as shown in Table 11.2, “The biosdevname Naming Convention”. Note that unless the system is a Dell system, or biosdevname is explicitly enabled as described in Section 11.6.2, “Enabling and Disabling the Feature”, the systemd naming scheme will take precedence.
Table 11.2. The biosdevname Naming Convention
Device Old Name New Name
Embedded network interface (LOM) eth[0123…] em[1234…][a]
PCI card network interface eth[0123…] p<slot>p<ethernet port>[b]
Virtual function eth[0123…] p<slot>p<ethernet port>_<virtual interface>[c]
[a] New enumeration starts at 1.
[b] For example: p3p4
[c] For example: p3p4_1

11.6.1. System Requirements

The biosdevname program uses information from the system's BIOS, specifically the type 9 (System Slot) and type 41 (Onboard Devices Extended Information) fields contained within the SMBIOS. If the system's BIOS does not have SMBIOS version 2.6 or higher and this data, the new naming convention will not be used. Most older hardware does not support this feature because of a lack of BIOSes with the correct SMBIOS version and field information. For BIOS or SMBIOS version information, contact your hardware vendor.
For this feature to take effect, the biosdevname package must also be installed. To install it, issue the following command as root: 
~]# yum install biosdevname

11.6.2. Enabling and Disabling the Feature

To disable this feature, pass the following option on the boot command line, both during and after installation: 
biosdevname=0
To enable this feature, pass the following option on the boot command line, both during and after installation: 
biosdevname=1
Unless the system meets the minimum requirements, this option will be ignored and the system will use the systemd naming scheme as described in the beginning of the chapter.
If the biosdevname install option is specified, it must remain as a boot option for the lifetime of the system.

11.7. Notes for Administrators

Many system customization files can include network interface names, and thus will require updates if moving a system from the old convention to the new convention. If you use the new naming convention, you will also need to update network interface names in areas such as custom iptables rules, scripts altering irqbalance, and other similar configuration files. Also, enabling this change for installation will require modification to existing kickstart files that use device names through the ksdevice parameter; these kickstart files will need to be updated to use the network device's MAC address or the network device's new name.

Note

The maximum interface name length is defined by the kernel headers and is a global limit, affecting all applications.

11.8. Controlling the Selection of Network Device Names

Device naming can be controlled in the following manner:
By identifying the network interface device
Setting the MAC address in an ifcfg file using the HWADDR directive enables it to be identified by udev. The name will be taken from the string given by the DEVICE directive, which by convention is the same as the ifcfg suffix. For example, ifcfg-enp1s0.
By turning on or off biosdevname
The name provided by biosdevname will be used (if biosdevname can determine one).
By turning on or off the systemd-udev naming scheme
The name provided by systemd-udev will be used (if systemd-udev can determine one).

11.9. Troubleshooting Network Device Naming

Predictable interface names will be assigned for each interface, if applicable, as per the procedure described in Section 11.2, “Understanding the Device Renaming Procedure”. To view the list of possible names udev will use, issue a command in the following form as root: 
~]# udevadm info /sys/class/net/ifname | grep ID_NET_NAME
where ifname is one of the interfaces listed by the following command: 
~]$ ls /sys/class/net/
One of the possible names will be applied by udev according to the rules as described in Section 11.2, “Understanding the Device Renaming Procedure”, and summarized here:
  • /usr/lib/udev/rules.d/60-net.rules - from initscripts,
  • /usr/lib/udev/rules.d/71-biosdevname.rules - from biosdevname,
  • /usr/lib/udev/rules.d/80-net-name-slot.rules - from systemd
From the above list of rule files it can be seen that if interface naming is done through initscripts or biosdevname it always takes precedence over udev native naming. However if initscripts renaming is not taking place and biosdevname is disabled, then to alter the interface names copy the 80-net-name-slot.rules from /usr to /etc and edit the file appropriately. In other words, comment out or arrange schemes to be used in a certain order.

Example 11.1. Some Interfaces Have Names from the Kernel Namespace (eth[0,1,2...]) While Others Are Successfully Renamed by udev

Mixed up schemes most likely means that either for some hardware there is no usable information provided by the kernel to udev, thus it could not figure out any names, or the information provided to udev is not suitable, for example non-unique device IDs. The latter is more common and the solution is to use a custom naming scheme in ifcfg files or alter which udev scheme is in use by editing 80-net-name-slot.rules.

Example 11.2. In /var/log/messages or the systemd Journal, Renaming Is Seen to Be Done Twice for Each Interface

Systems with the naming scheme encoded in ifcfg files but which do not have a regenerated initrd image are likely to encounter this issue. The interface name is initially assigned (through biosdevname or udev or dracut parameters on the kernel command line) during early-boot while still in initrd. Then after switching to real rootfs, renaming is done a second time and a new interface name is determined by the /usr/lib/udev/rename_device binary spawned by udev because of processing 60-net.rules. You can safely ignore such messages.

Example 11.3. Using Naming Scheme in ifcfg Files with ethX Names Does Not Work

Red Hat Enterprise Linux does not provide a way to consistently apply the ethX naming convention except under very specific circumstances.
The udev rules, which set an interface to a specific name, fail if the requested name is already in use by some other interface. This includes the functionality provided by the /usr/lib/udev/rules.d/60-net.rules file.
Kernel uses the ethX naming convention at boot time when it enumerates network devices. The ethX names are inconsistent across various reboots, and thus they are unpredictable. Consequently, attempting to use udev to rename an interface to a predictable name or to reorder the unpredictable ethX names given by the kernel fails.
Using the ethX names works correctly for the following scenarios:
  • The system has only one network interface.
  • When used for virtio NICs in Red Hat Enterprise Linux 7 virtual machine guests. See the KVM Paravirtualized (virtio) Drivers and Network Configuration chapters in the Virtualization Deployment and Administration Guide

Example 11.4. Setting net.ifnames=0 Results in Inconsistent enpXxX Names

If both systemd predictable interface naming (net.ifnames) and biosdevname naming schemes are disabled, network interfaces continue to use the unpredictable and potentially inconsistent ethX name originally given by the kernel.
Kernel always uses the enpXxX naming convention at boot when it enumerates network devices. Due to parallelization, the order of the kernel interface enumeration is expected to vary across reboots. Red Hat Enterprise Linux relies on either systemd predictable interface naming scheme or the biosdevname naming scheme to rename the kernel unpredictable ethX interfaces in a predictable way to a name which is always consistent across reboots.
For more information about network adapter naming conventions, see the Is it safe to set net.ifnames=0 in RHEL7? Knowledge Centered Support article on the Red Hat Customer Portal.

Example 11.5. Limitations for Prefixes of Ethernet Interfaces

The prefix that you choose must meet the following requirements:
  • It consists of ASCII characters.
  • It is an alpha-numeric string.
  • It is shorter than 16 characters.
  • It does not conflict with any other well-known prefix used for network interface naming, such as eth, eno, ens, and em.

11.10. Additional Resources

Installed Documentation

  • udev(7) man page — Describes the Linux dynamic device management daemon, udevd.
  • systemd(1) man page — Describes systemd system and service manager.
  • biosdevname(1) man page — Describes the utility for obtaining the BIOS-given name of a device.

Online Documentation

Chapter 12. Configuring Policy-based Routing to Define Alternative Routes

By default, the kernel in RHEL decides where to forward network packets based on the destination address using a routing table. Policy-based routing enables you to configure complex routing scenarios. For example, you can route packets based on various criteria, such as the source address, packet metadata, or protocol.
This section describes of how to configure policy-based routing using NetworkManager.

Note

On systems that use NetworkManager, only the nmcli utility supports setting routing rules and assigning routes to specific tables.

12.1. Routing Traffic from a Specific Subnet to a Different Default Gateway

This section describes how to configure RHEL as a router that, by default, routes all traffic to internet provider A using the default route. Using policy-based routing, RHEL routes traffic received from the internal workstations subnet to provider B.
The procedure assumes the following network topology:
Activate a Connection

Figure 12.1. Activate a Connection

Prerequisites
  • The RHEL router you want to set up in the procedure has four network interfaces:
    • The enp7s0 interface is connected to the network of provider A. The gateway IP in the provider’s network is 198.51.100.2, and the network uses a /30 network mask.
    • The enp1s0 interface is connected to the network of provider B. The gateway IP in the provider’s network is 192.0.2.2, and the network uses a /30 network mask.
    • The enp8s0 interface is connected to the 10.0.0.0/24 subnet with internal workstations.
    • The enp9s0 interface is connected to the 203.0.113.0/24 subnet with the company’s servers.
  • Hosts in the internal workstations subnet use 10.0.0.1 as default gateway. In the procedure, you assign this IP address to the enp8s0 network interface of the router.
  • Hosts in the server subnet use 203.0.113.1 as default gateway. In the procedure, you assign this IP address to the enp9s0 network interface of the router.
  • The firewalld service is enabled and active, which is the default.
Procedure
  1. Configure the network interface to provider A: 
    # nmcli connection add type ethernet con-name Provider-A ifname enp7s0 ipv4.method manual ipv4.addresses 198.51.100.1/30 ipv4.gateway 198.51.100.2 ipv4.dns 198.51.100.200 connection.zone external
    The nmcli connection add command creates a NetworkManager connection profile. The following list describes the options of the command:
    • type ethernet: Defines that the connection type is Ethernet.
    • con-name connection_name: Sets the name of the profile. Use a meaningful name to avoid confusion.
    • ifname network_device: Sets the network interface.
    • ipv4.method manual: Enables to configure a static IP address.
    • ipv4.addresses IP_address/subnet_mask: Sets the IPv4 addresses and subnet mask.
    • ipv4.gateway IP_address: Sets the default gateway address.
    • ipv4.dns IP_of_DNS_server: Sets the IPv4 address of the DNS server.
    • connection.zone firewalld_zone: Assigns the network interface to the defined firewalld zone. Note that firewalld automatically enables masquerading interfaces assigned to the external zone.
  2. Configure the network interface to provider B: 
    # nmcli connection add type ethernet con-name Provider-B ifname enp1s0 ipv4.method manual ipv4.addresses 192.0.2.1/30 ipv4.routes "0.0.0.0/1 192.0.2.2 table=5000, 128.0.0.0/1 192.0.2.2 table=5000" connection.zone external
    This command uses the ipv4.routes parameter instead of ipv4.gateway to set the default gateway. This is required to assign the default gateway for this connection to a different routing table (5000) than the default. NetworkManager automatically creates this new routing table when the connection is activated.

    Note

    The nmcli utility does not support using 0.0.0.0/0 for the default gateway in ipv4.gateway. To work around this problem, the command creates separate routes for both the 0.0.0.0/1 and 128.0.0.0/1 subnets, which covers also the full IPv4 address space.
  3. Configure the network interface to the internal workstations subnet: 
    # nmcli connection add type ethernet con-name Internal-Workstations ifname enp8s0 ipv4.method manual ipv4.addresses 10.0.0.1/24 ipv4.routes "10.0.0.0/24 src=192.0.2.1 table=5000" ipv4.routing-rules "priority 5 from 10.0.0.0/24 table 5000" connection.zone trusted
    This command uses the ipv4.routes parameter to add a static route to the routing table with ID 5000. This static route for the 10.0.0.0/24 subnet uses the IP of the local network interface to provider B (192.0.2.1) as next hop.
    Additionally, the command uses the ipv4.routing-rules parameter to add a routing rule with priority 5 that routes traffic from the 10.0.0.0/24 subnet to table 5000. Low values have a high priority.
    Note that the syntax in the ipv4.routing-rules parameter is the same as in an ip route add command, except that ipv4.routing-rules always requires specifying a priority.
  4. Configure the network interface to the server subnet: 
    # nmcli connection add type ethernet con-name Servers ifname enp9s0 ipv4.method manual ipv4.addresses 203.0.113.1/24 connection.zone trusted
Verification Steps
  1. On a RHEL host in the internal workstation subnet:
    1. Install the traceroute package: 
      # yum install traceroute
    2. Use the traceroute utility to display the route to a host on the internet: 
      # traceroute redhat.com
traceroute to redhat.com (209.132.183.105), 30 hops max, 60 byte packets
 1  10.0.0.1 (10.0.0.1)     0.337 ms  0.260 ms  0.223 ms
 2  192.0.2.1 (192.0.2.1)   0.884 ms  1.066 ms  1.248 ms
 ...
      The output of the command displays that the router sends packets over 192.0.2.1, which is the network of provider B.
  2. On a RHEL host in the server subnet:
    1. Install the traceroute package: 
      # yum install traceroute
    2. Use the traceroute utility to display the route to a host on the internet: 
      # traceroute redhat.com
traceroute to redhat.com (209.132.183.105), 30 hops max, 60 byte packets
 1  203.0.113.1 (203.0.113.1)    2.179 ms  2.073 ms  1.944 ms
 2  198.51.100.2 (198.51.100.2)  1.868 ms  1.798 ms  1.549 ms
 ...
      The output of the command displays that the router sends packets over 198.51.100.2, which is the network of provider A.
Troubleshooting Steps
On the RHEL router:
  1. Display the rule list: 
    # ip rule list
0:	from all lookup local
5: from 10.0.0.0/24 lookup 5000
32766:	from all lookup main
32767:	from all lookup default
  2. Display the routes in table 5000: 
    # ip route list table 5000
0.0.0.0/1 via 192.0.2.2 dev enp1s0 proto static metric 100
10.0.0.0/24 dev enp8s0 proto static scope link src 192.0.2.1 metric 102
128.0.0.0/1 via 192.0.2.2 dev enp1s0 proto static metric 100
  3. Display which interfaces are assigned to which firewall zones: 
    # firewall-cmd --get-active-zones
external
  interfaces: enp1s0 enp7s0
trusted
  interfaces: enp8s0 enp9s0
  4. Verify that the external zone has masquerading enabled: 
    # firewall-cmd --info-zone=external
external (active)
  target: default
  icmp-block-inversion: no
  interfaces: enp1s0 enp7s0
  sources:
  services: ssh
  ports:
  protocols:
  masquerade: yes
  ...
Additional Resources
  • For further details about the ipv4.* parameters you can set in the nmcli connection add command, see the IPv4 settings section in the nm-settings(5) man page.
  • For further details about the connection.* parameters you can set in the nmcli connection add command, see the Connection settings section in the nm-settings(5) man page.
  • For further details about managing NetworkManager connections using nmcli, see the Connection management commands section in the nmcli(1) man page.

Part III. InfiniBand and RDMA Networking

This part discusses how to set up RDMA, InfiniBand, and IP over InfiniBand network connections.

Chapter 13. Configure InfiniBand and RDMA Networks

13.1. Understanding InfiniBand and RDMA technologies

InfiniBand refers to two distinct things. The first is a physical link-layer protocol for InfiniBand networks. The second is a higher level programming API called the InfiniBand Verbs API. The InfiniBand Verbs API is an implementation of a remote direct memory access (RDMA) technology.
RDMA provides direct access from the memory of one computer to the memory of another without involving either computer’s operating system. This technology enables high-throughput, low-latency networking with low CPU utilization, which is especially useful in massively parallel computer clusters.
In a typical IP data transfer, application X on machine A sends some data to application Y on machine B. As part of the transfer, the kernel on machine B must first receive the data, decode the packet headers, determine that the data belongs to application Y, wake up application Y, wait for application Y to perform a read syscall into the kernel, then it must manually copy the data from the kernel's own internal memory space into the buffer provided by application Y. This process means that most network traffic must be copied across the system's main memory bus at least twice (once when the host adapter uses DMA to put the data into the kernel-provided memory buffer, and again when the kernel moves the data to the application's memory buffer) and it also means the computer must execute a number of context switches to switch between kernel context and application Y context. Both of these things impose extremely high CPU loads on the system when network traffic is flowing at very high rates and can make other tasks to slow down.
RDMA communications differ from normal IP communications because they bypass kernel intervention in the communication process, and in the process greatly reduce the CPU overhead normally needed to process network communications. The RDMA protocol allows the host adapter in the machine to know when a packet comes in from the network, which application should receive that packet, and where in the application's memory space it should go. Instead of sending the packet to the kernel to be processed and then copied into the user application's memory, it places the contents of the packet directly in the application's buffer without any further intervention necessary. However, it cannot be accomplished using the standard Berkeley Sockets API that most IP networking applications are built upon, so it must provide its own API, the InfiniBand Verbs API, and applications must be ported to this API before they can use RDMA technology directly.
Red Hat Enterprise Linux 7 supports both the InfiniBand hardware and the InfiniBand Verbs API. In addition, there are two additional supported technologies that allow the InfiniBand Verbs API to be utilized on non-InfiniBand hardware:
  • The Internet Wide Area RDMA Protocol (iWARP)
    iWARP is a computer networking protocol that implements remote direct memory access (RDMA) for efficient data transfer over Internet Protocol (IP) networks.
  • The RDMA over Converged Ethernet (RoCE) protocol, which later renamed to InfiniBand over Ethernet (IBoE).
    RoCE is a network protocol that allows remote direct memory access (RDMA) over an Ethernet network.

Prerequisites

Both iWARP and RoCE technologies have a normal IP network link layer as their underlying technology, and so the majority of their configuration is actually covered in Chapter 3, Configuring IP Networking. For the most part, once their IP networking features are properly configured, their RDMA features are all automatic and will show up as long as the proper drivers for the hardware are installed. The kernel drivers are always included with each kernel Red Hat provides, however the user-space drivers must be installed manually if the InfiniBand package group was not selected at machine install time.
Since Red Hat Enterprise Linux 7.4, all RDMA user-space drivers are merged into the rdma-core package. To install all supported iWARP, RoCE or InfiniBand user-space drivers, enter as root: 
~]# yum install libibverbs
If you are using Priority Flow Control (PFC) and mlx4-based cards, then edit /etc/modprobe.d/mlx4.conf to instruct the driver which packet priority is configured for the “no-drop” service on the Ethernet switches the cards are plugged into and rebuild the initramfs to include the modified file. Newer mlx5-based cards auto-negotiate PFC settings with the switch and do not need any module option to inform them of the “no-drop” priority or priorities.
To set the Mellanox cards to use one or both ports in Ethernet mode, see Section 13.5.4, “Configuring Mellanox cards for Ethernet operation”.
With these driver packages installed (in addition to the normal RDMA packages typically installed for any InfiniBand installation), a user should be able to utilize most of the normal RDMA applications to test and see RDMA protocol communication taking place on their adapters. However, not all of the programs included in Red Hat Enterprise Linux 7 properly support iWARP or RoCE/IBoE devices. This is because the connection establishment protocol on iWARP in particular is different than it is on real InfiniBand link-layer connections. If the program in question uses the librdmacm connection management library, it handles the differences between iWARP and InfiniBand silently and the program should work. If the application tries to do its own connection management, then it must specifically support iWARP or else it does not work.

13.2. Transferring Data Using RoCE

RDMA over Converged Ethernet (RoCE) is a network protocol that enables remote direct memory access (RDMA) over an Ethernet network. There are two RoCE versions, RoCE v1 and RoCE v2, depending on the network adapter used.

RoCE v1
The RoCE v1 protocol is an Ethernet link layer protocol with ethertype 0x8915 that enables communication between any two hosts in the same Ethernet broadcast domain. RoCE v1 is the default version for RDMA Connection Manager (RDMA_CM) when using the ConnectX-3 network adapter.
RoCE v2
The RoCE v2 protocol exists on top of either the UDP over IPv4 or the UDP over IPv6 protocol. The UDP destination port number 4791 has been reserved for RoCE v2. Since Red Hat Enterprise Linux 7.5, RoCE v2 is the default version for RDMA_CM when using the ConnectX-3 Pro, ConnectX-4, ConnectX-4 Lx and ConnectX-5 network adapters. Hardware supports both RoCE v1 and RoCE v2.
RDMA Connection Manager (RDMA_CM) is used to set up a reliable connection between a client and a server for transferring data. RDMA_CM provides an RDMA transport-neutral interface for establishing connections. The communication is over a specific RDMA device, and data transfers are message-based.

Prerequisites

An RDMA_CM session requires one of the following:
  • Both client and server support the same RoCE mode.
  • A client supports RoCE v1 and a server RoCE v2.
Since a client determines the mode of the connection, the following cases are possible:
A successful connection:
If a client is in RoCE v1 or in RoCE v2 mode depending on the network card and the driver used, the corresponding server must have the same version to create a connection. Also, the connection is successful if a client is in RoCE v1 and a server in RoCE v2 mode.
A failed connection:
If a client is in RoCE v2 and the corresponding server is in RoCE v1, no connection can be established. In this case, update the driver or the network adapter of the corresponding server, see Section 13.2, “Transferring Data Using RoCE”
Table 13.1. RoCE Version Defaults Using RDMA_CM
ClientServerDefault setting
RoCE v1RoCE v1Connection
RoCE v1RoCE v2Connection
RoCE v2RoCE v2Connection
RoCE v2RoCE v1No connection
That RoCE v2 on the client and RoCE v1 on the server are not compatible. To resolve this issue, force both the server and client-side environment to communicate over RoCE v1. This means to force hardware that supports RoCE v2 to use RoCE v1:

Procedure 13.1. Changing the Default RoCE Mode When the Hardware Is Already Running in Roce v2

  1. Change into the /sys/kernel/config/rdma_cm directory to et the RoCE mode: 
    ~]# cd /sys/kernel/config/rdma_cm
  2. Enter the ibstat command with an Ethernet network device to display the status. For example, for mlx5_0: 
    ~]$ ibstat mlx5_0
    CA 'mlx5_0'
        CA type: MT4115
        Number of ports: 1
        Firmware version: 12.17.1010
        Hardware version: 0
        Node GUID: 0x248a0703004bf0a4
        System image GUID: 0x248a0703004bf0a4
        Port 1:
            State: Active
            Physical state: LinkUp
            Rate: 40
            Base lid: 0
            LMC: 0
            SM lid: 0
            Capability mask: 0x04010000
            Port GUID: 0x268a07fffe4bf0a4
            Link layer: Ethernet
  3. Create a directory for the mlx5_0 device: 
    ~]# mkdir mlx5_0
  4. Display the RoCE mode in the default_roce_mode file in the tree format: 
    ~]# cd mlx5_0
    ~]$ tree
└── ports
    └── 1
        ├── default_roce_mode
        └── default_roce_tos
    ~]$ cat /sys/kernel/config/rdma_cm/mlx5_0/ports/1/default_roce_mode
    RoCE v2
  5. Change the default RoCE mode: 
    ~]# echo "RoCE v1" > /sys/kernel/config/rdma_cm/mlx5_0/ports/1/default_roce_mode
  6. View the changes: 
    ~]$ cat /sys/kernel/config/rdma_cm/mlx5_0/ports/1/default_roce_mode
    RoCE v1

13.3. Configuring Soft-RoCE

RoCE can be implemented both in the hardware and in the software. Soft-RoCE is the software implementation of the RDMA transport.

Prerequisites

Since Red Hat Enterprise Linux 7.4, the Soft-RoCE driver is already merged into the kernel. The user-space driver also is merged into the rdma-core package. Soft-RoCE is also known as RXE. To start, stop and configure RXE, use the rxe_cfg script. To view options for rxe_cfg, enter rxe_cfg help.

Procedure 13.2. Configuring Soft-RoCE

  1. As the root user, enter the following command to display the current configuration status of RXE: 
    ~]# rxe_cfg
  rdma_rxe module not loaded
  Name        Link  Driver   Speed   NMTU  IPv4_addr  RDEV  RMTU
  igb_1       yes   igb
  mlx4_1      no    mlx4_en
  mlx4_2      no    mlx4_en
  2. To load the RXE kernel module and start RXE, enter as root: 
    ~]# rxe_cfg start
  Name        Link  Driver   Speed   NMTU  IPv4_addr  RDEV  RMTU
  igb_1       yes   igb
  mlx4_1      no    mlx4_en
  mlx4_2      no    mlx4_en
    Optionally, to verify that the RXE kernel module is loaded, enter: 
    ~]# lsmod |grep rdma_rxe
  rdma_rxe              111129  0
  ip6_udp_tunnel         12755  1 rdma_rxe
  udp_tunnel             14423  1 rdma_rxe
  ib_core               236827  15 rdma_cm,ib_cm,iw_cm,rpcrdma,mlx4_ib,ib_srp,ib_ucm,ib_iser,ib_srpt,ib_umad,ib_uverbs,rdma_rxe,rdma_ucm,ib_ipoib,ib_isert
  3. Before adding a new RXE device over an Ethernet interface, the corresponding interface should be opened and has a valid IP address assigned. To add a new RXE device, for example igb_1: 
    ~]# rxe_cfg add igb_1
    ~]# rxe_cfg status
  Name        Link  Driver   Speed   NMTU  IPv4_addr  RDEV  RMTU
  igb_1       yes   igb                               rxe0  1024  (3)
  mlx4_1      no    mlx4_en
  mlx4_2      no    mlx4_en
    The rxe0 in the RDEV column indicates that rxe is enabled for the igb_1 device.
  4. To verify the status of an RXE device, use the ibv_devices command: 
    ~]# ibv_devices
  device                 node GUID
  ------              ----------------
  mlx4_0              0002c90300b3cff0
  rxe0                a2369ffffe018294
    Alternatively, enter the ibstat for a detailed status: 
    ~]# ibstat rxe0
CA 'rxe0'
    CA type:
    Number of ports: 1
    Firmware version:
    Hardware version:
    Node GUID: 0xa2369ffffe018294
    System image GUID: 0x0000000000000000
    Port 1:
        State: Active
        Physical state: LinkUp
        Rate: 2.5
        Base lid: 0
        LMC: 0
        SM lid: 0
        Capability mask: 0x00890000
        Port GUID: 0xa2369ffffe018294
        Link layer: Ethernet

Removing an RXE device

If you want to remove an RXE device, enter: 
~]# rxe_cfg remove igb_1

Verifying Connectivity of an RXE device

The following examples show how to verify connectivity of an RXE device on the server and client side.

Example 13.1. Verifying Connectivity of an RXE device on the Server Side

~]$ ibv_rc_pingpong -d rxe0 -g 0
  local address:  LID 0x0000, QPN 0x000012, PSN 0xe2965f, GID fe80::290:faff:fe29:486a
  remote address: LID 0x0000, QPN 0x000011, PSN 0x4bf206, GID fe80::290:faff:fe29:470a
8192000 bytes in 0.05 seconds = 1244.06 Mbit/sec
1000 iters in 0.05 seconds = 52.68 usec/iter

Example 13.2. Verifying Connectivity of an RXE device on the Client Side

~]$ ibv_rc_pingpong -d rxe0 -g 0 172.31.40.4
  local address:  LID 0x0000, QPN 0x000011, PSN 0x4bf206, GID fe80::290:faff:fe29:470a
  remote address: LID 0x0000, QPN 0x000012, PSN 0xe2965f, GID fe80::290:faff:fe29:486a
 8192000 bytes in 0.05 seconds = 1245.72 Mbit/sec
 1000 iters in 0.05 seconds = 52.61 usec/iter

13.5. Configuring the Base RDMA Subsystem

Startup of the rdma service is automatic. When RDMA capable hardware, whether InfiniBand or iWARP or RoCE/IBoE is detected, udev instructs systemd to start the rdma service.  
~]# systemctl status rdma
● rdma.service - Initialize the iWARP/InfiniBand/RDMA stack in the kernel
   Loaded: loaded (/usr/lib/systemd/system/rdma.service; disabled; vendor preset: disabled)
   Active: inactive (dead)
     Docs: file:/etc/rdma/rdma.conf
Users need not enable the rdma service, but they can if they want to force it on all the time. To do that, enter the following command as root: 
~]# systemctl enable rdma

13.5.1. Configuration of the rdma.conf file

The rdma service reads /etc/rdma/rdma.conf to find out which kernel-level and user-level RDMA protocols the administrator wants to be loaded by default. Users should edit this file to turn various drivers on or off.
The various drivers that can be enabled and disabled are:
  • IPoIB — This is an IP network emulation layer that allows IP applications to run over InfiniBand networks.
  • SRP — This is the SCSI Request Protocol. It allows a machine to mount a remote drive or drive array that is exported through the SRP protocol on the machine as though it were a local hard disk.
  • SRPT — This is the target mode, or server mode, of the SRP protocol. This loads the kernel support necessary for exporting a drive or drive array for other machines to mount as though it were local on their machine. Further configuration of the target mode support is required before any devices will actually be exported. See the documentation in the targetd and targetcli packages for further information.
  • ISER — This is a low-level driver for the general iSCSI layer of the Linux kernel that provides transport over InfiniBand networks for iSCSI devices.
  • RDS — This is the Reliable Datagram Service in the Linux kernel. It is not enabled in Red Hat Enterprise Linux 7 kernels and so cannot be loaded.

13.5.2. Usage of 70-persistent-ipoib.rules

The rdma package provides the file /etc/udev.d/rules.d/70-persistent-ipoib.rules. This udev rules file is used to rename IPoIB devices from their default names (such as ib0 and ib1) to more descriptive names. Users must edit this file to change how their devices are named. First, find out the GUID address for the device to be renamed: 
~]$ ip link show ib0
8: ib0: >BROADCAST,MULTICAST,UP,LOWER_UP< mtu 65520 qdisc pfifo_fast state UP mode DEFAULT qlen 256
    link/infiniband 80:00:02:00:fe:80:00:00:00:00:00:00:f4:52:14:03:00:7b:cb:a1 brd 00:ff:ff:ff:ff:12:40:1b:ff:ff:00:00:00:00:00:00:ff:ff:ff:ff
Immediately after link/infiniband is the 20 byte hardware address for the IPoIB interface. The final 8 bytes of the address, marked in bold above, is all that is required to make a new name. Users can make up whatever naming scheme suits them. For example, use a device_fabric naming convention such as mlx4_ib0 if a mlx4 device is connected to an ib0 subnet fabric. The only thing that is not recommended is to use the standard names, like ib0 or ib1, as these can conflict with the kernel assigned automatic names. Next, add an entry in the rules file. Copy the existing example in the rules file, replace the 8 bytes in the ATTR{address} entry with the highlighted 8 bytes from the device to be renamed, and enter the new name to be used in the NAME field.

13.5.3. Relaxing memlock restrictions for users

RDMA communications require that physical memory in the computer be pinned (meaning that the kernel is not allowed to swap that memory out to a paging file in the event that the overall computer starts running short on available memory). Pinning memory is normally a very privileged operation. In order to allow users other than root to run large RDMA applications, it will likely be necessary to increase the amount of memory that non-root users are allowed to pin in the system. This is done by adding a file in the /etc/security/limits.d/ directory with contents such as the following: 
~]$ more /etc/security/limits.d/rdma.conf
# configuration for rdma tuning
*       soft    memlock         unlimited
*       hard    memlock         unlimited
# rdma tuning end

13.5.4. Configuring Mellanox cards for Ethernet operation

Certain hardware from Mellanox is capable of running in either InfiniBand or Ethernet mode. These cards generally default to InfiniBand. Users can set the cards to Ethernet mode. There is currently support for setting the mode only on ConnectX family hardware (which uses either the mlx5 or mlx4 driver).
To configure Mellanox mlx5 cards, use the mstconfig program from the mstflint package. For more details, see the Configuring Mellanox mlx5 cards in Red Hat Enterprise Linux 7 Knowledge Base article on the Red Hat Customer Portal.
To configure Mellanox mlx4 cards, use mstconfig to set the port types on the card as described in the Knowledge Base article. If mstconfig does not support your card, edit the /etc/rdma/mlx4.conf file and follow the instructions in that file to set the port types properly for RoCE/IBoE usage. In this case is also necessary to rebuild the initramfs to make sure the updated port settings are copied into the initramfs.
Once the port type has been set, if one or both ports are set to Ethernet and mstconfig was not used to set the port types, then users might see this message in their logs: 
mlx4_core 0000:05:00.0: Requested port type for port 1 is not supported on this HCA
This is normal and does not affect operation. The script responsible for setting the port type has no way of knowing when the driver has finished switching port 2 to the requested type internally, and from the time that the script issues a request for port 2 to switch until that switch is complete, the attempts to set port 1 to a different type get rejected. The script retries until the command succeeds or until a timeout has passed indicating that the port switch never completed.

13.5.5. Connecting to a Remote Linux SRP Target

The SCSI RDMA Protocol (SRP) is a network protocol that enables a system to use RDMA to access SCSI devices that are attached to another system. To allow an SRP initiator to connect an SRP target on the SRP target side, you must add an access control list (ACL) entry for the host channel adapter (HCA) port used in the initiator.
ACL IDs for HCA ports are not unique. The ACL IDs depend on the GID format of the HCAs. HCAs that use the same driver, for example ib_qib, can have different format of GIDs. The ACL ID also depends on how you initiate the connection request.

Connecting to a Remote Linux SRP Target: High-Level Overview

  1. Prepare the target side:
    1. Create storage back end. For example get the /dev/sdc1 partition: 
      /> /backstores/block create vol1 /dev/sdc1
    2. Create an SRP target: 
      /> /srpt create 0xfe80000000000000001175000077dd7e
    3. Create a LUN based on the back end created in step a: 
      /> /srpt/ib.fe80000000000000001175000077dd7e/luns create /backstores/block/vol1
    4. Create a Node ACL for the remote SRP client: 
      /> /srpt/ib.fe80000000000000001175000077dd7e/acls create 0x7edd770000751100001175000077d708
      Note that the Node ACL is different for srp_daemon and ibsrpdm.
  2. Initiate an SRP connection with srp_daemon or ibsrpdm for the client side: 
    [root@initiator]# srp_daemon -e -n -i qib0 -p 1 -R 60 &
    [root@initiator]# ibsrpdm -c -d /dev/infiniband/umad0 > /sys/class/infiniband_srp/srp-qib0-1/add_target
  3. Optional. It is recommended to verify the SRP connection with different tools, such as lsscsi or dmesg.

Procedure 13.3. Connecting to a Remote Linux SRP Target with srp_daemon or ibsrpdm

  1. Use the ibstat command on the target to determine the State and Port GUID values. The HCA must be in Active state. The ACL ID is based on the Port GUID: 
    [root@target]# ibstat
CA 'qib0'
	CA type: InfiniPath_QLE7342
	Number of ports: 1
	Firmware version:
	Hardware version: 2
	Node GUID: 0x001175000077dd7e
	System image GUID: 0x001175000077dd7e
	Port 1:
		State: Active
		Physical state: LinkUp
		Rate: 40
		Base lid: 1
		LMC: 0
		SM lid: 1
		Capability mask: 0x0769086a
		Port GUID: 0x001175000077dd7e
		Link layer: InfiniBand
  2. Get the SRP target ID, which is based on the GUID of the HCA port. Note that you need a dedicated disk partition as a back end for a SRP target, for example /dev/sdc1. The following command replaces the default prefix of fe80, removes the colon, and adds the new prefix to the remainder of the string: 
    [root@target]# ibstatus | grep '<default-gid>' | sed -e 's/<default-gid>://' -e 's/://g' | grep 001175000077dd7e
fe80000000000000001175000077dd7e
  3. Use the targetcli tool to create the LUN vol1 on the block device, create an SRP target, and export the LUN: 
    [root@target]# targetcli


/> /backstores/block create vol1 /dev/sdc1
Created block storage object vol1 using /dev/sdc1.
/> /srpt create 0xfe80000000000000001175000077dd7e
Created target ib.fe80000000000000001175000077dd7e.
/> /srpt/ib.fe80000000000000001175000077dd7e/luns create /backstores/block/vol1
Created LUN 0.
/> ls /
o- / ............................................................................. [...]
  o- backstores .................................................................. [...]
  | o- block ...................................................... [Storage Objects: 1]
  | | o- vol1 ............................... [/dev/sdc1 (77.8GiB) write-thru activated]
  | o- fileio ..................................................... [Storage Objects: 0]
  | o- pscsi ...................................................... [Storage Objects: 0]
  | o- ramdisk .................................................... [Storage Objects: 0]
  o- iscsi ................................................................ [Targets: 0]
  o- loopback ............................................................. [Targets: 0]
  o- srpt ................................................................. [Targets: 1]
    o- ib.fe80000000000000001175000077dd7e ............................... [no-gen-acls]
      o- acls ................................................................ [ACLs: 0]
      o- luns ................................................................ [LUNs: 1]
        o- lun0 ............................................... [block/vol1 (/dev/sdc1)]
/>
  4. Use the ibstat command on the initiator to check if the state is Active and determine the Port GUID: 
    [root@initiator]# ibstat
CA 'qib0'
	CA type: InfiniPath_QLE7342
	Number of ports: 1
	Firmware version:
	Hardware version: 2
	Node GUID: 0x001175000077d708
	System image GUID: 0x001175000077d708
	Port 1:
		State: Active
		Physical state: LinkUp
		Rate: 40
		Base lid: 2
		LMC: 0
		SM lid: 1
		Capability mask: 0x07690868
		Port GUID: 0x001175000077d708
		Link layer: InfiniBand
  5. Use the following command to scan without connecting to a remote SRP target. The target GUID shows that the initiator had found remote target. The ID string shows that the remote target is a Linux software target (ib_srpt.ko). 
    [root@initiator]# srp_daemon -a -o
IO Unit Info:
    port LID:        0001
    port GID:        fe80000000000000001175000077dd7e
    change ID:       0001
    max controllers: 0x10

    controller[  1]
        GUID:      001175000077dd7e
        vendor ID: 000011
        device ID: 007322
        IO class : 0100
        ID:        Linux SRP target
        service entries: 1
            service[  0]: 001175000077dd7e / SRP.T10:001175000077dd7e
  6. To verify the SRP connection, use the lsscsi command to list SCSI devices and compare the lsscsi output before and after the initiator connects to target. 
    [root@initiator]# lsscsi
[0:0:10:0]   disk    IBM-ESXS ST9146803SS      B53C  /dev/sda
  7. To connect to a remote target without configuring a valid ACL for the initiator port, which is expected to fail, use the following commands for srp_daemon or ibsrpdm: 
    [root@initiator]# srp_daemon -e -n -i qib0 -p 1 -R 60 &
[1] 4184

    [root@initiator]# ibsrpdm -c -d /dev/infiniband/umad0 > /sys/class/infiniband_srp/srp-qib0-1/add_target
  8. The output of the dmesg shows why the SRP connection operation failed. In a later step, the dmesg command on the target side is used to make the situation clear. 
    [root@initiator]# dmesg -c
[ 1230.059652] scsi host5: ib_srp: REJ received
[ 1230.059659] scsi host5: ib_srp: SRP LOGIN from fe80:0000:0000:0000:0011:7500:0077:d708 to fe80:0000:0000:0000:0011:7500:0077:dd7e REJECTED, reason 0x00010006
[ 1230.073792] scsi host5: ib_srp: Connection 0/2 failed
[ 1230.078848] scsi host5: ib_srp: Sending CM DREQ failed
  9. Because of failed LOGIN, the output of the lsscsi command is the same as in the earlier step. 
    [root@initiator]# lsscsi
[0:0:10:0]   disk    IBM-ESXS ST9146803SS      B53C  /dev/sda
  10. Using the dmesg on the target side (ib_srpt.ko) provides an explanation of why LOGIN failed. Also, the output contains the valid ACL ID provided by srp_daemon: 0x7edd770000751100001175000077d708. 
    [root@target]# dmesg
[ 1200.303001] ib_srpt Received SRP_LOGIN_REQ with i_port_id 0x7edd770000751100:0x1175000077d708, t_port_id 0x1175000077dd7e:0x1175000077dd7e and it_iu_len 260 on port 1 (guid=0xfe80000000000000:0x1175000077dd7e)
[ 1200.322207] ib_srpt Rejected login because no ACL has been configured yet for initiator 0x7edd770000751100001175000077d708.
  11. Use the targetcli tool to add a valid ACL: 
    [root@target]# targetcli
targetcli shell version 2.1.fb41
Copyright 2011-2013 by Datera, Inc and others.
For help on commands, type 'help'.

/> /srpt/ib.fe80000000000000001175000077dd7e/acls create 0x7edd770000751100001175000077d708
Created Node ACL for ib.7edd770000751100001175000077d708
Created mapped LUN 0.
  12. Verify the SRP LOGIN operation:
    1. Wait for 60 seconds to allow srp_daemon to re-try logging in: 
      [root@initiator]# sleep 60
    2. Verify the SRP LOGIN operation: 
      [root@initiator]# lsscsi
[0:0:10:0]   disk    IBM-ESXS ST9146803SS      B53C  /dev/sda
[7:0:0:0] disk LIO-ORG vol1 4.0 /dev/sdb
    3. For a kernel log of SRP target discovery, use: 
      [root@initiator]# dmesg -c
[ 1354.182072] scsi host7: SRP.T10:001175000077DD7E
[ 1354.187258] scsi 7:0:0:0: Direct-Access     LIO-ORG  vol1             4.0  PQ: 0 ANSI: 5
[ 1354.208688] scsi 7:0:0:0: alua: supports implicit and explicit TPGS
[ 1354.215698] scsi 7:0:0:0: alua: port group 00 rel port 01
[ 1354.221409] scsi 7:0:0:0: alua: port group 00 state A non-preferred supports TOlUSNA
[ 1354.229147] scsi 7:0:0:0: alua: Attached
[ 1354.233402] sd 7:0:0:0: Attached scsi generic sg1 type 0
[ 1354.233694] sd 7:0:0:0: [sdb] 163258368 512-byte logical blocks: (83.5 GB/77.8 GiB)
[ 1354.235127] sd 7:0:0:0: [sdb] Write Protect is off
[ 1354.235128] sd 7:0:0:0: [sdb] Mode Sense: 43 00 00 08
[ 1354.235550] sd 7:0:0:0: [sdb] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
[ 1354.255491] sd 7:0:0:0: [sdb] Attached SCSI disk
[ 1354.265233] scsi host7: ib_srp: new target: id_ext 001175000077dd7e ioc_guid 001175000077dd7e pkey ffff service_id 001175000077dd7e sgid fe80:0000:0000:0000:0011:7500:0077:d708 dgid fe80:0000:0000:0000:0011:7500:0077:dd7e
xyx

13.6. Configuring the Subnet Manager

13.6.1. Determining Necessity

Most InfiniBand switches come with an embedded subnet manager. However, if a more up to date subnet manager is required than the one in the switch firmware, or if more complete control than the switch manager allows is required, Red Hat Enterprise Linux 7 includes the opensm subnet manager. All InfiniBand networks must have a subnet manager running for the network to function. This is true even when doing a simple network of two machines with no switch and the cards are plugged in back to back, a subnet manager is required for the link on the cards to come up. It is possible to have more than one, in which case one will act as controller, and any other subnet managers will act as ports that will take over should the controller subnet manager fail.

13.6.2. Configuring the opensm main configuration file

The opensm program keeps its main configuration file in /etc/rdma/opensm.conf. Users may edit this file at any time and edits will be kept on upgrade. There is extensive documentation of the options in the file itself. However, for the two most common edits needed, setting the GUID to bind to and the PRIORITY to run with, it is highly recommended that the opensm.conf file is not edited but instead edit /etc/sysconfig/opensm. If there are no edits to the base /etc/rdma/opensm.conf file, it will get upgraded whenever the opensm package is upgraded. As new options are added to this file regularly, this makes it easier to keep the current configuration up to date. If the opensm.conf file has been changed, then on upgrade, it might be necessary to merge new options into the edited file.

13.6.3. Configuring the opensm startup options

The options in the /etc/sysconfig/opensm file control how the subnet manager is actually started, as well as how many copies of the subnet manager are started. For example, a dual port InfiniBand card, with each port plugged into physically separate networks, will need a copy of the subnet manager running on each port. The opensm subnet manager will only manage one subnet per instance of the application and must be started once for each subnet that needs to be managed. In addition, if there is more than one opensm server, then set the priorities on each server to control which are to be ports and which are to be controller.
The file /etc/sysconfig/opensm is used to provide a simple means to set the priority of the subnet manager and to control which GUID the subnet manager binds to. There is an extensive explanation of the options in the /etc/sysconfig/opensm file itself. Users need only read and follow the directions in the file itself to enable failover and multifabric operation of opensm.

13.6.4. Creating a P_Key definition

By default, opensm.conf looks for the file /etc/rdma/partitions.conf to get a list of partitions to create on the fabric. All fabrics must contain the 0x7fff subnet, and all switches and all hosts must belong to that fabric. Any other partition can be created in addition to that, and all hosts and all switches do not have to be members of these additional partitions. This allows an administrator to create subnets akin to Ethernet’s VLANs on InfiniBand fabrics. If a partition is defined with a given speed, such as 40 Gbps, and there is a host on the network unable to do 40 Gbps, then that host will be unable to join the partition even if it has permission to do so as it will be unable to match the speed requirements, therefore it is recommended that the speed of a partition be set to the slowest speed of any host with permission to join the partition. If a faster partition for some subset of hosts is required, create a different partition with the higher speed.
The following partition file would result in a default 0x7fff partition at a reduced speed of 10 Gbps, and a partition of 0x0002 with a speed of 40 Gbps: 
~]$ more /etc/rdma/partitions.conf
# For reference:
# IPv4 IANA reserved multicast addresses:
#   http://www.iana.org/assignments/multicast-addresses/multicast-addresses.txt
# IPv6 IANA reserved multicast addresses:
#   http://www.iana.org/assignments/ipv6-multicast-addresses/ipv6-multicast-addresses.xml
#
# mtu =
#   1 = 256
#   2 = 512
#   3 = 1024
#   4 = 2048
#   5 = 4096
#
# rate =
#   2  =   2.5 GBit/s
#   3  =  10   GBit/s
#   4  =  30   GBit/s
#   5  =   5   GBit/s
#   6  =  20   GBit/s
#   7  =  40   GBit/s
#   8  =  60   GBit/s
#   9  =  80   GBit/s
#   10 = 120   GBit/s

Default=0x7fff, rate=3, mtu=4, scope=2, defmember=full:
        ALL, ALL_SWITCHES=full;
Default=0x7fff, ipoib, rate=3, mtu=4, scope=2:
        mgid=ff12:401b::ffff:ffff       # IPv4 Broadcast address
        mgid=ff12:401b::1               # IPv4 All Hosts group
        mgid=ff12:401b::2               # IPv4 All Routers group
        mgid=ff12:401b::16              # IPv4 IGMP group
        mgid=ff12:401b::fb              # IPv4 mDNS group
        mgid=ff12:401b::fc              # IPv4 Multicast Link Local Name Resolution group
        mgid=ff12:401b::101             # IPv4 NTP group
        mgid=ff12:401b::202             # IPv4 Sun RPC
        mgid=ff12:601b::1               # IPv6 All Hosts group
        mgid=ff12:601b::2               # IPv6 All Routers group
        mgid=ff12:601b::16              # IPv6 MLDv2-capable Routers group
        mgid=ff12:601b::fb              # IPv6 mDNS group
        mgid=ff12:601b::101             # IPv6 NTP group
        mgid=ff12:601b::202             # IPv6 Sun RPC group
        mgid=ff12:601b::1:3             # IPv6 Multicast Link Local Name Resolution group
        ALL=full, ALL_SWITCHES=full;

ib0_2=0x0002, rate=7, mtu=4, scope=2, defmember=full:
        ALL, ALL_SWITCHES=full;
ib0_2=0x0002, ipoib, rate=7, mtu=4, scope=2:
        mgid=ff12:401b::ffff:ffff       # IPv4 Broadcast address
        mgid=ff12:401b::1               # IPv4 All Hosts group
        mgid=ff12:401b::2               # IPv4 All Routers group
        mgid=ff12:401b::16              # IPv4 IGMP group
        mgid=ff12:401b::fb              # IPv4 mDNS group
        mgid=ff12:401b::fc              # IPv4 Multicast Link Local Name Resolution group
        mgid=ff12:401b::101             # IPv4 NTP group
        mgid=ff12:401b::202             # IPv4 Sun RPC
        mgid=ff12:601b::1               # IPv6 All Hosts group
        mgid=ff12:601b::2               # IPv6 All Routers group
        mgid=ff12:601b::16              # IPv6 MLDv2-capable Routers group
        mgid=ff12:601b::fb              # IPv6 mDNS group
        mgid=ff12:601b::101             # IPv6 NTP group
        mgid=ff12:601b::202             # IPv6 Sun RPC group
        mgid=ff12:601b::1:3             # IPv6 Multicast Link Local Name Resolution group
        ALL=full, ALL_SWITCHES=full;

13.6.5. Enabling opensm

Users need to enable the opensm service as it is not enabled by default when installed. Issue the following command as root: 
~]# systemctl enable opensm

13.7. Testing Early InfiniBand RDMA operation

Note

This section applies only to InfiniBand devices. Since iWARP and RoCE/IBoE devices are IP based devices, users should proceed to the section on testing RDMA operations once IPoIB has been configured and the devices have IP addresses.
Once the rdma service is enabled, and the opensm service (if needed) is enabled, and the proper user-space library for the specific hardware has been installed, user space rdma operation should be possible. Simple test programs from the libibverbs-utils package are helpful in determining that RDMA operations are working properly. The ibv_devices program will show which devices are present in the system and the ibv_devinfo command will give detailed information about each device. For example: 
~]$ ibv_devices
    device                 node GUID
    ------              ----------------
    mlx4_0              0002c903003178f0
    mlx4_1              f4521403007bcba0
~]$ ibv_devinfo -d mlx4_1
hca_id: mlx4_1
        transport:                      InfiniBand (0)
        fw_ver:                         2.30.8000
        node_guid:                      f452:1403:007b:cba0
        sys_image_guid:                 f452:1403:007b:cba3
        vendor_id:                      0x02c9
        vendor_part_id:                 4099
        hw_ver:                         0x0
        board_id:                       MT_1090120019
        phys_port_cnt:                  2
                port:   1
                        state:                  PORT_ACTIVE (4)
                        max_mtu:                4096 (5)
                        active_mtu:             2048 (4)
                        sm_lid:                 2
                        port_lid:               2
                        port_lmc:               0x01
                        link_layer:             InfiniBand

                port:   2
                        state:                  PORT_ACTIVE (4)
                        max_mtu:                4096 (5)
                        active_mtu:             4096 (5)
                        sm_lid:                 0
                        port_lid:               0
                        port_lmc:               0x00
                        link_layer:             Ethernet
~]$ ibstat mlx4_1
CA 'mlx4_1'
        CA type: MT4099
        Number of ports: 2
        Firmware version: 2.30.8000
        Hardware version: 0
        Node GUID: 0xf4521403007bcba0
        System image GUID: 0xf4521403007bcba3
        Port 1:
                State: Active
                Physical state: LinkUp
                Rate: 56
                Base lid: 2
                LMC: 1
                SM lid: 2
                Capability mask: 0x0251486a
                Port GUID: 0xf4521403007bcba1
                Link layer: InfiniBand
        Port 2:
                State: Active
                Physical state: LinkUp
                Rate: 40
                Base lid: 0
                LMC: 0
                SM lid: 0
                Capability mask: 0x04010000
                Port GUID: 0xf65214fffe7bcba2
                Link layer: Ethernet
The ibv_devinfo and ibstat commands output slightly different information (such as port MTU exists in ibv_devinfo but not in ibstat output, and the Port GUID exists in ibstat output but not in ibv_devinfo output), and a few things are named differently (for example, the Base local identifier (LID) in ibstat output is the same as the port_lid output of ibv_devinfo)
Simple ping programs, such as ibping from the infiniband-diags package, can be used to test RDMA connectivity. The ibping program uses a client-server model. You must first start an ibping server on one machine, then run ibping as a client on another machine and tell it to connect to the ibping server. Since we are wanting to test the base RDMA capability, we need to use an RDMA specific address resolution method instead of IP addresses for specifying the server.
On the server machine, the user can use the ibv_devinfo and ibstat commands to print out the port_lid (or Base lid) and the Port GUID of the port they want to test (assuming port 1 of the above interface, the port_lid/Base LID is 2 and Port GUID is 0xf4521403007bcba1)). Then start ibping with the necessary options to bind specifically to the card and port to be tested, and also specifying ibping should run in server mode. You can see the available options to ibping by passing -? or --help, but in this instance we will need either the -S or --Server option and for binding to the specific card and port we will need either -C or --Ca and -P or --Port. Note: port in this instance does not denote a network port number, but denotes the physical port number on the card when using a multi-port card. To test connectivity to the RDMA fabric using, for example, the second port of a multi-port card, requires telling ibping to bind to port 2 on the card. When using a single port card, or testing the first port on a card, this option is not needed. For example: 
~]$ ibping -S -C mlx4_1 -P 1
Then change to the client machine and run ibping. Make note of either the port GUID of the port the server ibping program is bound to, or the local identifier (LID) of the port the server ibping program is bound to. Also, take note which card and port in the client machine is physically connected to the same network as the card and port that was bound to on the server. For example, if the second port of the first card on the server was bound to, and that port is connected to a secondary RDMA fabric, then on the client specify whichever card and port are necessary to also be connected to that secondary fabric. Once these things are known, run the ibping program as a client and connect to the server using either the port LID or GUID that was collected on the server as the address to connect to. For example: 
~]$ ibping -c 10000 -f -C mlx4_0 -P 1 -L 2
--- rdma-host.example.com.(none) (Lid 2) ibping statistics ---
10000 packets transmitted, 10000 received, 0% packet loss, time 816 ms
rtt min/avg/max = 0.032/0.081/0.446 ms
or 
~]$ ibping -c 10000 -f -C mlx4_0 -P 1 -G 0xf4521403007bcba1 \
--- rdma-host.example.com.(none) (Lid 2) ibping statistics ---
10000 packets transmitted, 10000 received, 0% packet loss, time 769 ms
rtt min/avg/max = 0.027/0.076/0.278 ms
This outcome verifies that end to end RDMA communications are working for user space applications.
The following error may be encountered: 
~]$ ibv_devinfo
libibverbs: Warning: no userspace device-specific driver found for /sys/class/infiniband_verbs/uverbs0
No IB devices found
This error indicates that the necessary user-space library is not installed. The administrator will need to install one of the user-space libraries (as appropriate for their hardware) listed in section Section 13.4, “InfiniBand and RDMA related software packages”. On rare occasions, this can happen if a user installs the wrong arch type for the driver or for libibverbs. For example, if libibverbs is of arch x86_64, and libmlx4 is installed but is of type i686, then this error can result.

Note

Many sample applications prefer to use host names or addresses instead of LIDs to open communication between the server and client. For those applications, it is necessary to set up IPoIB before attempting to test end-to-end RDMA communications. The ibping application is unusual in that it will accept simple LIDs as a form of addressing, and this allows it to be a simple test that eliminates possible problems with IPoIB addressing from the test scenario and therefore gives us a more isolated view of whether or not simple RDMA communications are working.

13.8. Configuring IPoIB

13.8.1. Understanding the role of IPoIB

As mentioned in Section 1.1, “Comparing IP to non-IP Networks”, most networks are IP networks. InfiniBand is not. The role of IPoIB is to provide an IP network emulation layer on top of InfiniBand RDMA networks. This allows existing applications to run over InfiniBand networks unmodified. However, the performance of those applications is considerably lower than if the application were written to use RDMA communication natively. Since most InfiniBand networks have some set of applications that really must get all of the performance they can out of the network, and then some other applications for which a degraded rate of performance is acceptable if it means that the application does not need to be modified to use RDMA communications, IPoIB is there to allow those less critical applications to run on the network as they are.
Because both iWARP and RoCE/IBoE networks are actually IP networks with RDMA layered on top of their IP link layer, they have no need of IPoIB. As a result, the kernel will refuse to create any IPoIB devices on top of iWARP or RoCE/IBoE RDMA devices.

13.8.2. Understanding IPoIB communication modes

IPoIB devices can be configured to run in either datagram or connected mode. The difference is in what type of queue pair the IPoIB layer attempts to open with the machine at the other end of the communication. For datagram mode, an unreliable, disconnected queue pair is opened. For connected mode, a reliable, connected queue pair is opened.
When using datagram mode, the unreliable, disconnected queue pair type does not allow any packets larger than the InfiniBand link-layer’s MTU. The IPoIB layer adds a 4 byte IPoIB header on top of the IP packet being transmitted. As a result, the IPoIB MTU must be 4 bytes less than the InfiniBand link-layer MTU. As 2048 is a common InfiniBand link-layer MTU, the common IPoIB device MTU in datagram mode is 2044.
When using connected mode, the reliable, connected queue pair type allows messages that are larger than the InfiniBand link-layer MTU and the host adapter handles packet segmentation and reassembly at each end. As a result, there is no size limit imposed on the size of IPoIB messages that can be sent by the InfiniBand adapters in connected mode. However, there is still the limitation that an IP packet only has a 16 bit size field, and is therefore limited to 65535 as the maximum byte count. The maximum allowed MTU is actually smaller than that because we have to account for various TCP/IP headers that must also fit in that size. As a result, the IPoIB MTU in connected mode is capped at 65520 in order to make sure there is sufficient room for all needed TCP headers.
The connected mode option generally has higher performance, but it also consumes more kernel memory. Because most systems care more about performance than memory consumption, connected mode is the most commonly used mode.
However, if a system is configured for connected mode, it must still send multicast traffic in datagram mode (the InfiniBand switches and fabric cannot pass multicast traffic in connected mode) and it will also fall back to datagram mode when communicating with any hosts not configured for connected mode. Administrators should be aware that if they intend to run programs that send multicast data, and those programs try to send multicast data up to the maximum MTU on the interface, then it is necessary to configure the interface for datagram operation or find some way to configure the multicast application to cap their packet send size at a size that will fit in datagram sized packets.

13.8.3. Understanding IPoIB hardware addresses

IPoIB devices have a 20 byte hardware addresses. The deprecated utility ifconfig is unable to read all 20 bytes and should never be used to try and find the correct hardware address for an IPoIB device. The ip utilities from the iproute package work properly.
The first 4 bytes of the IPoIB hardware address are flags and the queue pair number. The next 8 bytes are the subnet prefix. When the IPoIB device is first created, it will have the default subnet prefix of 0xfe:80:00:00:00:00:00:00. The device will use the default subnet prefix (0xfe80000000000000) until it makes contact with the subnet manager, at which point it will reset the subnet prefix to match what the subnet manager has configured it to be. The final 8 bytes are the GUID address of the InfiniBand port that the IPoIB device is attached to. Because both the first 4 bytes and the next 8 bytes can change from time to time, they are not used or matched against when specifying the hardware address for an IPoIB interface. Section Section 13.5.2, “Usage of 70-persistent-ipoib.rules” explains how to derive the address by leaving the first 12 bytes out of the ATTR{address} field in the udev rules file so that device matching will happen reliably. When configuring IPoIB interfaces, the HWADDR field of the configuration file can contain all 20 bytes, but only the last 8 bytes are actually used to match against and find the hardware specified by a configuration file. However, if the TYPE=InfiniBand entry is not spelled correctly in the device configuration file, and ifup-ib is not the actual script used to open the IPoIB interface, then an error about the system being unable to find the hardware specified by the configuration will be issued. For IPoIB interfaces, the TYPE= field of the configuration file must be either InfiniBand or infiniband (the entry is case sensitive, but the scripts will accept these two specific spellings).

13.8.4. Understanding InfiniBand P_Key subnets

An InfiniBand fabric can be logically segmented into virtual subnets by the use of different P_Key subnets. This is highly analogous to using VLANs on Ethernet interfaces. All switches and hosts must be a member of the default P_Key subnet, but administrators can create additional subnets and limit members of those subnets to subsets of the hosts or switches in the fabric. A P_Key subnet must be defined by the subnet manager before a host can use it. See section Section 13.6.4, “Creating a P_Key definition” for information on how to define a P_Key subnet using the opensm subnet manager. For IPoIB interfaces, once a P_Key subnet has been created, we can create additional IPoIB configuration files specifically for those P_Key subnets. Just like VLAN interfaces on Ethernet devices, each IPoIB interface will behave as though it were on a completely different fabric from other IPoIB interfaces that share the same link but have different P_Key values.
There are special requirements for the names of IPoIB P_Key interfaces. All IPoIB P_Keys range from 0x0000 to 0x7fff, and the high bit, 0x8000, denotes that membership in a P_Key is full membership instead of partial membership. The Linux kernel’s IPoIB driver only supports full membership in P_Key subnets, so for any subnet that Linux can connect to, the high bit of the P_Key number will always be set. That means that if a Linux computer joins P_Key 0x0002, its actual P_Key number once joined will be 0x8002, denoting that we are full members of P_Key 0x0002. For this reason, when creating a P_Key definition in an opensm partitions.conf file as depicted in section Section 13.6.4, “Creating a P_Key definition”, it is required to specify a P_Key value without 0x8000, but when defining the P_Key IPoIB interfaces on the Linux clients, add the 0x8000 value to the base P_Key value.

13.8.5. Configure InfiniBand Using the Text User Interface, nmtui

The text user interface tool nmtui can be used to configure InfiniBand in a terminal window. Issue the following command to start the tool: 
~]$ nmtui
The text user interface appears. Any invalid command prints a usage message.
To navigate, use the arrow keys or press Tab to step forwards and press Shift+Tab to step back through the options. Press Enter to select an option. The Space bar toggles the status of a check box.
From the starting menu, select Edit a connection. Select Add, the New Connection screen opens.
The NetworkManager Text User Interface Add an InfiniBand Connection menu

Figure 13.1. The NetworkManager Text User Interface Add an InfiniBand Connection menu

Select InfiniBand, the Edit connection screen opens. Follow the on-screen prompts to complete the configuration.
The NetworkManager Text User Interface Configuring a InfiniBand Connection menu

Figure 13.2. The NetworkManager Text User Interface Configuring a InfiniBand Connection menu

See Section 13.8.9.1, “Configuring the InfiniBand Tab” for definitions of the InfiniBand terms.
See Section 3.2, “Configuring IP Networking with nmtui” for information on installing nmtui.

13.8.6. Configure IPoIB using the command-line tool, nmcli

First determine if renaming the default IPoIB device(s) is required, and if so, follow the instructions in section Section 13.5.2, “Usage of 70-persistent-ipoib.rules” to rename the devices using udev renaming rules. Users can force the IPoIB interfaces to be renamed without performing a reboot by removing the ib_ipoib kernel module and then reloading it as follows: 
~]$ rmmod ib_ipoib
~]$ modprobe ib_ipoib
Once the devices have the name required, use the nmcli tool to create the IPoIB interface(s). The following examples display two ways:

Example 13.3. Creating and modifying IPoIB in two separate commands.

~]$ nmcli con add type infiniband con-name mlx4_ib0 ifname mlx4_ib0 transport-mode connected mtu 65520
Connection 'mlx4_ib0' (8029a0d7-8b05-49ff-a826-2a6d722025cc) successfully added.
~]$ nmcli con edit mlx4_ib0

===| nmcli interactive connection editor |===

Editing existing 'infiniband' connection: 'mlx4_ib0'

Type 'help' or '?' for available commands.
Type 'describe [>setting<.>prop<]' for detailed property description.

You may edit the following settings: connection, infiniband, ipv4, ipv6
nmcli> set infiniband.mac-address 80:00:02:00:fe:80:00:00:00:00:00:00:f4:52:14:03:00:7b:cb:a3
nmcli> save
Connection 'mlx4_ib3' (8029a0d7-8b05-49ff-a826-2a6d722025cc) successfully updated.
nmcli> quit
or you can run nmcli c add and nmcli c modify in one command, as follows:

Example 13.4. Creating and modifying IPoIB in one command.

nmcli con add type infiniband con-name mlx4_ib0 ifname mlx4_ib0 transport-mode connected mtu 65520  infiniband.mac-address 80:00:02:00:fe:80:00:00:00:00:00:00:f4:52:14:03:00:7b:cb:a3
At these points, an IPoIB interface named mlx4_ib0 has been created and set to use connected mode, with the maximum connected mode MTU, DHCP for IPv4 and IPv6. If using IPoIB interfaces for cluster traffic and an Ethernet interface for out-of-cluster communications, it is likely that disabling default routes and any default name server on the IPoIB interfaces will be required. This can be done as follows: 
~]$ nmcli con edit mlx4_ib0

===| nmcli interactive connection editor |===

Editing existing 'infiniband' connection: 'mlx4_ib0'

Type 'help' or '?' for available commands.
Type 'describe [>setting<.>prop<]' for detailed property description.

You may edit the following settings: connection, infiniband, ipv4, ipv6
nmcli> set ipv4.ignore-auto-dns yes
nmcli> set ipv4.ignore-auto-routes yes
nmcli> set ipv4.never-default true
nmcli> set ipv6.ignore-auto-dns yes
nmcli> set ipv6.ignore-auto-routes yes
nmcli> set ipv6.never-default true
nmcli> save
Connection 'mlx4_ib0' (8029a0d7-8b05-49ff-a826-2a6d722025cc) successfully updated.
nmcli> quit
If a P_Key interface is required, create one using nmcli as follows: 
~]$ nmcli con add type infiniband con-name mlx4_ib0.8002 ifname mlx4_ib0.8002 parent mlx4_ib0 p-key 0x8002
Connection 'mlx4_ib0.8002' (4a9f5509-7bd9-4e89-87e9-77751a1c54b4) successfully added.
~]$ nmcli con modify mlx4_ib0.8002 infiniband.mtu 65520 infiniband.transport-mode connected ipv4.ignore-auto-dns yes ipv4.ignore-auto-routes yes ipv4.never-default true ipv6.ignore-auto-dns yes ipv6.ignore-auto-routes yes ipv6.never-default true

13.8.7. Configure IPoIB Using the command line

First determine if renaming the default IPoIB device(s) is required, and if so, follow the instructions in section Section 13.5.2, “Usage of 70-persistent-ipoib.rules” to rename the devices using udev renaming rules. Users can force the IPoIB interfaces to be renamed without performing a reboot by removing the ib_ipoib kernel module and then reloading it as follows: 
~]$ rmmod ib_ipoib
~]$ modprobe ib_ipoib
Once the devices have the name required, administrators can create ifcfg files with their preferred editor to control the devices. A typical IPoIB configuration file with static IPv4 addressing looks as follows: 
~]$ more ifcfg-mlx4_ib0
DEVICE=mlx4_ib0
TYPE=InfiniBand
ONBOOT=yes
HWADDR=80:00:00:4c:fe:80:00:00:00:00:00:00:f4:52:14:03:00:7b:cb:a1
BOOTPROTO=none
IPADDR=172.31.0.254
PREFIX=24
NETWORK=172.31.0.0
BROADCAST=172.31.0.255
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
MTU=65520
CONNECTED_MODE=yes
NAME=mlx4_ib0
The DEVICE field must match the custom name created in any udev renaming rules. The NAME entry need not match the device name. If the GUI connection editor is started, the NAME field is what is used to present a name for this connection to the user. The TYPE field must be InfiniBand in order for InfiniBand options to be processed properly. CONNECTED_MODE is either yes or no, where yes will use connected mode and no will use datagram mode for communications (see section Section 13.8.2, “Understanding IPoIB communication modes”).
For P_Key interfaces, this is a typical configuration file: 
~]$ more ifcfg-mlx4_ib0.8002
DEVICE=mlx4_ib0.8002
PHYSDEV=mlx4_ib0
PKEY=yes
PKEY_ID=2
TYPE=InfiniBand
ONBOOT=yes
HWADDR=80:00:00:4c:fe:80:00:00:00:00:00:00:f4:52:14:03:00:7b:cb:a1
BOOTPROTO=none
IPADDR=172.31.2.254
PREFIX=24
NETWORK=172.31.2.0
BROADCAST=172.31.2.255
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
MTU=65520
CONNECTED_MODE=yes
NAME=mlx4_ib0.8002
For all P_Key interface files, the PHYSDEV directive is required and must be the name of the parent device. The PKEY directive must be set to yes, and PKEY_ID must be the number of the interface (either with or without the 0x8000 membership bit added in). The device name, however, must be the four digit hexadecimal representation of the PKEY_ID combined with the 0x8000 membership bit using the logical OR operator as follows: 
NAME=${PHYSDEV}.$((0x8000 | $PKEY_ID))
By default, the PKEY_ID in the file is treated as a decimal number and converted to hexadecimal and then combined using the logical OR operator with 0x8000 to arrive at the proper name for the device, but users may specify the PKEY_ID in hexadecimal by prepending the standard 0x prefix to the number.

13.8.8. Testing an RDMA network after IPoIB is configured

Once IPoIB is configured, it is possible to use IP addresses to specify RDMA devices. Due to the ubiquitous nature of using IP addresses and host names to specify machines, most RDMA applications use this as their preferred, or in some cases only, way of specifying remote machines or local devices to connect to.
To test the functionality of the IPoIB layer, it is possible to use any standard IP network test tool and provide the IP address of the IPoIB devices to be tested. For example, the ping command between the IP addresses of the IPoIB devices should now work.
There are two different RDMA performance testing packages included with Red Hat Enterprise Linux, qperf and perftest. Either of these may be used to further test the performance of an RDMA network.
However, when using any of the applications that are part of the perftest package, or using the qperf application, there is a special note on address resolution. Even though the remote host is specified using an IP address or host name of the IPoIB device, it is allowed for the test application to actually connect through a different RDMA interface. The reason for this is because the process of converting from the host name or IP address to an RDMA address allows any valid RDMA address pair between the two machines to be used. If there are multiple ways for the client to connect to the server, then the programs might choose to use a different path if there is a problem with the path specified. For example, if there are two ports on each machine connected to the same InfiniBand subnet, and an IP address for the second port on each machine is given, it is likely that the program will find the first port on each machine is a valid connection method and use them instead. In this case, command-line options to any of the perftest programs can be used to tell them which card and port to bind to, as was done with ibping in Section 13.7, “Testing Early InfiniBand RDMA operation”, in order to ensure that testing occurs over the specific ports required to be tested. For qperf, the method of binding to ports is slightly different. The qperf program operates as a server on one machine, listening on all devices (including non-RDMA devices). The client may connect to qperf using any valid IP address or host name for the server. Qperf will first attempt to open a data connection and run the requested test(s) over the IP address or host name given on the client command line, but if there is any problem using that address, qperf will fall back to attempting to run the test on any valid path between the client and server. For this reason, to force qperf to test over a specific link, use the -loc_id and -rem_id options to the qperf client in order to force the test to run on a specific link.

13.8.9. Configure IPoIB Using a GUI

To configure an InfiniBand connection using a graphical tool, use nm-connection-editor

Procedure 13.4. Adding a New InfiniBand Connection Using nm-connection-editor

  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
  2. Click the Add button. The Choose a Connection Type window appears. Select InfiniBand and click Create. The Editing InfiniBand connection 1 window appears.
  3. On the InfiniBand tab, select the transport mode from the drop-down list you want to use for the InfiniBand connection.
  4. Enter the InfiniBand MAC address.
  5. Review and confirm the settings and then click the Save button.
  6. Edit the InfiniBand-specific settings by referring to Section 13.8.9.1, “Configuring the InfiniBand Tab”.

Procedure 13.5. Editing an Existing InfiniBand Connection

Follow these steps to edit an existing InfiniBand connection.
  1. Enter nm-connection-editor in a terminal: 
    ~]$ nm-connection-editor
  2. Select the connection you want to edit and click the Edit button.
  3. Select the General tab.
  4. Configure the connection name, auto-connect behavior, and availability settings.
    Five settings in the Editing dialog are common to all connection types, see the General tab:
    • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the menu of the Network window.
    • Automatically connect to this network when it is available — Select this box if you want NetworkManager to auto-connect to this connection when it is available. See the section called “Editing an Existing Connection with control-center” for more information.
    • All users may connect to this network — Select this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 3.4.5, “Managing System-wide and Private Connection Profiles with a GUI” for details.
    • Automatically connect to VPN when using this connection — Select this box if you want NetworkManager to auto-connect to a VPN connection when it is available. Select the VPN from the drop-down menu.
    • Firewall Zone — Select the Firewall Zone from the drop-down menu. See the Red Hat Enterprise Linux 7 Security Guide for more information on Firewall Zones.
  5. Edit the InfiniBand-specific settings by referring to the Section 13.8.9.1, “Configuring the InfiniBand Tab”.
Saving Your New (or Modified) Connection and Making Further Configurations
Once you have finished editing your InfiniBand connection, click the Save button to save your customized configuration.
Then, to configure:
13.8.9.1. Configuring the InfiniBand Tab
If you have already added a new InfiniBand connection (see Procedure 13.4, “Adding a New InfiniBand Connection Using nm-connection-editor” for instructions), you can edit the InfiniBand tab to set the parent interface and the InfiniBand ID.
Transport mode
Datagram or Connected mode can be selected from the drop-down list. Select the same mode the rest of your IPoIB network is using.
Device MAC address
The MAC address of the InfiniBand capable device to be used for the InfiniBand network traffic.This hardware address field will be pre-filled if you have InfiniBand hardware installed.
MTU
Optionally sets a Maximum Transmission Unit (MTU) size to be used for packets to be sent over the InfiniBand connection.

13.8.10. Additional Resources

Installed Documentation
  • /usr/share/doc/initscripts-version/sysconfig.txt — Describes configuration files and their directives.
Online Documentation
https://www.kernel.org/doc/Documentation/infiniband/ipoib.txt
A description of the IPoIB driver. Includes references to relevant RFCs.

Part IV. Servers

This part discusses how to set up servers normally required for networking.

Note

To monitor and administer servers through a web browser, see Managing systems using the RHEL 7 web console.

Chapter 14. DHCP Servers

Dynamic Host Configuration Protocol (DHCP) is a network protocol that automatically assigns TCP/IP information to client machines. Each DHCP client connects to the centrally located DHCP server, which returns the network configuration (including the IP address, gateway, and DNS servers) of that client.

14.1. Why Use DHCP?

DHCP is useful for automatic configuration of client network interfaces. When configuring the client system, you can choose DHCP instead of specifying an IP address, netmask, gateway, or DNS servers. The client retrieves this information from the DHCP server. DHCP is also useful if you want to change the IP addresses of a large number of systems. Instead of reconfiguring all the systems, you can just edit one configuration file on the server for the new set of IP addresses. If the DNS servers for an organization changes, the changes happen on the DHCP server, not on the DHCP clients. When you restart the network or reboot the clients, the changes go into effect.
If an organization has a functional DHCP server correctly connected to a network, laptops and other mobile computer users can move these devices from office to office.
Note that administrators of DNS and DHCP servers, as well as any provisioning applications, should agree on the host name format used in an organization. See Section 6.1.1, “Recommended Naming Practices” for more information on the format of host names.

14.2. Configuring a DHCP Server

The dhcp package contains an Internet Systems Consortium (ISC) DHCP server. Install the package as root: 
~]# yum install dhcp
Installing the dhcp package creates a file, /etc/dhcp/dhcpd.conf, which is merely an empty configuration file. As root, issue the following command: 
~]# cat /etc/dhcp/dhcpd.conf
#
# DHCP Server Configuration file.
#   see /usr/share/doc/dhcp*/dhcpd.conf.example
#   see dhcpd.conf(5) man page
#
The example configuration file can be found at /usr/share/doc/dhcp-version;/dhcpd.conf.example. You should use this file to help you configure /etc/dhcp/dhcpd.conf, which is explained in detail below.
DHCP also uses the file /var/lib/dhcpd/dhcpd.leases to store the client lease database. See Section 14.2.2, “Lease Database” for more information.

14.2.1. Configuration File

The first step in configuring a DHCP server is to create the configuration file that stores the network information for the clients. Use this file to declare options for client systems.
The configuration file can contain extra tabs or blank lines for easier formatting. Keywords are case-insensitive and lines beginning with a hash sign (#) are considered comments.
There are two types of statements in the configuration file:
  • Parameters — State how to perform a task, whether to perform a task, or what network configuration options to send to the client.
  • Declarations — Describe the topology of the network, describe the clients, provide addresses for the clients, or apply a group of parameters to a group of declarations.
The parameters that start with the keyword option are referred to as options. These options control DHCP options; whereas, parameters configure values that are not optional or control how the DHCP server behaves.
Parameters (including options) declared before a section enclosed in curly brackets ({ }) are considered global parameters. Global parameters apply to all the sections below it.

Important

If the configuration file is changed, the changes do not take effect until the DHCP daemon is restarted with the command systemctl restart dhcpd.

Note

Instead of changing a DHCP configuration file and restarting the service each time, using the omshell command provides an interactive way to connect to, query, and change the configuration of a DHCP server. By using omshell, all changes can be made while the server is running. For more information on omshell, see the omshell man page.
In Example 14.1, “Subnet Declaration”, the routers, subnet-mask, domain-search, domain-name-servers, and time-offset options are used for any host statements declared below it.
For every subnet which will be served, and for every subnet to which the DHCP server is connected, there must be one subnet declaration, which tells the DHCP daemon how to recognize that an address is on that subnet. A subnet declaration is required for each subnet even if no addresses will be dynamically allocated to that subnet.
In this example, there are global options for every DHCP client in the subnet and a range declared. Clients are assigned an IP address within the range.

Example 14.1. Subnet Declaration

subnet 192.168.1.0 netmask 255.255.255.0 {
        option routers                  192.168.1.254;
        option subnet-mask              255.255.255.0;
        option domain-search              "example.com";
        option domain-name-servers       192.168.1.1;
        option time-offset              -18000;     # Eastern Standard Time
	range 192.168.1.10 192.168.1.100;
}
To configure a DHCP server that leases a dynamic IP address to a system within a subnet, modify the example values from Example 14.2, “Range Parameter”. It declares a default lease time, maximum lease time, and network configuration values for the clients. This example assigns IP addresses in the range 192.168.1.10 and 192.168.1.100 to client systems.

Example 14.2. Range Parameter

default-lease-time 600;
max-lease-time 7200;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.1.255;
option routers 192.168.1.254;
option domain-name-servers 192.168.1.1, 192.168.1.2;
option domain-search "example.com";
subnet 192.168.1.0 netmask 255.255.255.0 {
   range 192.168.1.10 192.168.1.100;
}
To assign an IP address to a client based on the MAC address of the network interface card, use the hardware ethernet parameter within a host declaration. As demonstrated in Example 14.3, “Static IP Address Using DHCP”, the host apex declaration specifies that the network interface card with the MAC address 00:A0:78:8E:9E:AA always receives the IP address 192.168.1.4.
Note that you can also use the optional parameter host-name to assign a host name to the client.

Example 14.3. Static IP Address Using DHCP

host apex {
   option host-name "apex.example.com";
   hardware ethernet 00:A0:78:8E:9E:AA;
   fixed-address 192.168.1.4;
}
Red Hat Enterprise Linux 7 supports assigning static IP addresses to InfiniBand IPoIB interfaces. However, as these interfaces do not have a normal hardware Ethernet address, a different method of specifying a unique identifier for the IPoIB interface must be used. The standard is to use the option dhcp-client-identifier= construct to specify the IPoIB interface’s dhcp-client-identifier field. The DHCP server host construct supports at most one hardware Ethernet and one dhcp-client-identifier entry per host stanza. However, there may be more than one fixed-address entry and the DHCP server will automatically respond with an address that is appropriate for the network that the DHCP request was received on.

Example 14.4. Static IP Address Using DHCP on Multiple Interfaces

If a machine has a complex configuration, for example two InfiniBand interfaces, and P_Key interfaces on each physical interface, plus an Ethernet connection, the following static IP construct could be used to serve this configuration: 
Host apex.0 {
    option host-name “apex.example.com”;
    hardware ethernet 00:A0:78:8E:9E:AA;
    option dhcp-client-identifier=ff:00:00:00:00:00:02:00:00:02:c9:00:00:02:c9:03:00:31:7b:11;
    fixed-address 172.31.0.50,172.31.2.50,172.31.1.50,172.31.3.50;
}

host apex.1 {
    option host-name “apex.example.com”;
    hardware ethernet 00:A0:78:8E:9E:AB;
    option dhcp-client-identifier=ff:00:00:00:00:00:02:00:00:02:c9:00:00:02:c9:03:00:31:7b:12;
    fixed-address 172.31.0.50,172.31.2.50,172.31.1.50,172.31.3.50;
}
In order to find the right dhcp-client-identifier for your device, you can usually use the prefix ff:00:00:00:00:00:02:00:00:02:c9:00 and then add the last 8 bytes of the IPoIB interface (which happens to also be the 8 byte GUID of the InfiniBand port the IPoIB interface is on). On some older controllers, this prefix is not correct. In that case, we recommend using tcpdump on the DHCP server to capture the incoming IPoIB DHCP request and gather the right dhcp-client-identifier from that capture. For example: 
]$ tcpdump -vv -i mlx4_ib0
tcpdump: listening on mlx4_ib0, link-type LINUX_SLL (Linux cooked), capture size 65535 bytes
23:42:44.131447 IP (tos 0x10, ttl 128, id 0, offset 0, flags [none], proto UDP (17), length 328)
    0.0.0.0.bootpc > 255.255.255.255.bootps: [udp sum ok] BOOTP/DHCP, Request, length 300, htype 32, hlen 0, xid 0x975cb024, Flags [Broadcast] (0x8000)
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message Option 53, length 1: Discover
            Hostname Option 12, length 10: "rdma-qe-03"
            Parameter-Request Option 55, length 18:
              Subnet-Mask, BR, Time-Zone, Classless-Static-Route
              Domain-Name, Domain-Name-Server, Hostname, YD
              YS, NTP, MTU, Option 119
              Default-Gateway, Classless-Static-Route, Classless-Static-Route-Microsoft, Static-Route
              Option 252, NTP
            Client-ID Option 61, length 20: hardware-type 255, 00:00:00:00:00:02:00:00:02:c9:00:00:02:c9:02:00:21:ac:c1
The above dump shows the Client-ID field. The hardware-type 255 corresponds to the initial ff: of the ID, the rest of the ID is then quoted exactly as it needs to appear in the DHCP configuration file.
All subnets that share the same physical network should be declared within a shared-network declaration as shown in Example 14.5, “Shared-network Declaration”. Parameters within the shared-network, but outside the enclosed subnet declarations, are considered to be global parameters. The name assigned to shared-network must be a descriptive title for the network, such as using the title “test-lab” to describe all the subnets in a test lab environment.

Example 14.5. Shared-network Declaration

shared-network name {
    option domain-search            "test.redhat.com";
    option domain-name-servers      ns1.redhat.com, ns2.redhat.com;
    option routers                  192.168.0.254;
    #more parameters for EXAMPLE shared-network
    subnet 192.168.1.0 netmask 255.255.252.0 {
        #parameters for subnet
        range 192.168.1.1 192.168.1.254;
    }
    subnet 192.168.2.0 netmask 255.255.252.0 {
        #parameters for subnet
        range 192.168.2.1 192.168.2.254;
    }
}
As demonstrated in Example 14.6, “Group Declaration”, the group declaration is used to apply global parameters to a group of declarations. For example, shared networks, subnets, and hosts can be grouped.

Example 14.6. Group Declaration

group {
   option routers                  192.168.1.254;
   option subnet-mask              255.255.255.0;
   option domain-search              "example.com";
   option domain-name-servers       192.168.1.1;
   option time-offset              -18000;     # Eastern Standard Time
   host apex {
      option host-name "apex.example.com";
      hardware ethernet 00:A0:78:8E:9E:AA;
      fixed-address 192.168.1.4;
   }
   host raleigh {
      option host-name "raleigh.example.com";
      hardware ethernet 00:A1:DD:74:C3:F2;
      fixed-address 192.168.1.6;
   }
}

Note

You can use the provided example configuration file as a starting point and add custom configuration options to it. To copy this file to the proper location, use the following command as root: 
~]# cp /usr/share/doc/dhcp-version_number/dhcpd.conf.example /etc/dhcp/dhcpd.conf
... where version_number is the DHCP version number.
For a complete list of option statements and what they do, see the dhcp-options(5) man page.

14.2.2. Lease Database

On the DHCP server, the file /var/lib/dhcpd/dhcpd.leases stores the DHCP client lease database. Do not change this file. DHCP lease information for each recently assigned IP address is automatically stored in the lease database. The information includes the length of the lease, to whom the IP address has been assigned, the start and end dates for the lease, and the MAC address of the network interface card that was used to retrieve the lease.
All times in the lease database are in Coordinated Universal Time (UTC), not local time.
The lease database is recreated from time to time so that it is not too large. First, all known leases are saved in a temporary lease database. The dhcpd.leases file is renamed dhcpd.leases~ and the temporary lease database is written to dhcpd.leases.
The DHCP daemon could be killed or the system could crash after the lease database has been renamed to the backup file but before the new file has been written. If this happens, the dhcpd.leases file does not exist, but it is required to start the service. Do not create a new lease file. If you do, all old leases are lost which causes many problems. The correct solution is to rename the dhcpd.leases~ backup file to dhcpd.leases and then start the daemon.

14.2.3. Starting and Stopping the Server

Important

When the DHCP server is started for the first time, it fails unless the dhcpd.leases file exists. You can use the command touch /var/lib/dhcpd/dhcpd.leases to create the file if it does not exist. If the same server is also running BIND as a DNS server, this step is not necessary, as starting the named service automatically checks for a dhcpd.leases file.
Do not create a new lease file on a system that was previously running. If you do, all old leases are lost which causes many problems. The correct solution is to rename the dhcpd.leases~ backup file to dhcpd.leases and then start the daemon.
To start the DHCP service, use the following command: 
systemctl start dhcpd.service
To stop the DHCP server, type: 
systemctl stop dhcpd.service
By default, the DHCP service does not start at boot time. For information on how to configure the daemon to start automatically at boot time, see Red Hat Enterprise Linux System Administrator's Guide.
If more than one network interface is attached to the system, but the DHCP server should only listen for DHCP requests on one of the interfaces, configure the DHCP server to listen only on that device. The DHCP daemon will only listen on interfaces for which it finds a subnet declaration in the /etc/dhcp/dhcpd.conf file.
This is useful for a firewall machine with two network cards. One network card can be configured as a DHCP client to retrieve an IP address to the Internet. The other network card can be used as a DHCP server for the internal network behind the firewall. Specifying only the network card connected to the internal network makes the system more secure because users cannot connect to the daemon through the Internet.
To specify command-line options, copy and then edit the dhcpd.service file as the root user. For example, as follows: 
~]# cp /usr/lib/systemd/system/dhcpd.service /etc/systemd/system/
~]# vi /etc/systemd/system/dhcpd.service
Edit the line under section [Service]: 
ExecStart=/usr/sbin/dhcpd -f -cf /etc/dhcp/dhcpd.conf -user dhcpd -group dhcpd --no-pid your_interface_name(s)
Then, as the root user, restart the service: 
~]# systemctl --system daemon-reload
~]# systemctl restart dhcpd
Command line options can be appended to ExecStart=/usr/sbin/dhcpd in the /etc/systemd/system/dhcpd.service unit file under section [Service]. They include:
  • -p portnum — Specifies the UDP port number on which dhcpd should listen. The default is port 67. The DHCP server transmits responses to the DHCP clients at a port number one greater than the UDP port specified. For example, if the default port 67 is used, the server listens on port 67 for requests and responds to the client on port 68. If a port is specified here and the DHCP relay agent is used, the same port on which the DHCP relay agent should listen must be specified. See Section 14.3, “DHCP Relay Agent” for details.
  • -f — Runs the daemon as a foreground process. This is mostly used for debugging.
  • -d — Logs the DHCP server daemon to the standard error descriptor. This is mostly used for debugging. If this is not specified, the log is written to /var/log/messages.
  • -cf filename — Specifies the location of the configuration file. The default location is /etc/dhcp/dhcpd.conf.
  • -lf filename — Specifies the location of the lease database file. If a lease database file already exists, it is very important that the same file be used every time the DHCP server is started. It is strongly recommended that this option only be used for debugging purposes on non-production machines. The default location is /var/lib/dhcpd/dhcpd.leases.
  • -q — Do not print the entire copyright message when starting the daemon.

14.3. DHCP Relay Agent

The DHCP Relay Agent (dhcrelay) enables the relay of DHCP and BOOTP requests from a subnet with no DHCP server on it to one or more DHCP servers on other subnets.
When a DHCP client requests information, the DHCP Relay Agent forwards the request to the list of DHCP servers specified when the DHCP Relay Agent is started. When a DHCP server returns a reply, the reply is broadcast or unicast on the network that sent the original request.
The DHCP Relay Agent for IPv4, dhcrelay, listens for DHCPv4 and BOOTP requests on all interfaces unless the interfaces are specified in /etc/sysconfig/dhcrelay with the INTERFACES directive. See Section 14.3.1, “Configure dhcrelay as a DHCPv4 and BOOTP relay agent”. The DHCP Relay Agent for IPv6, dhcrelay6, does not have this default behavior and interfaces to listen for DHCPv6 requests must be specified. See Section 14.3.2, “Configure dhcrelay as a DHCPv6 relay agent”.
dhcrelay can either be run as a DHCPv4 and BOOTP relay agent (by default) or as a DHCPv6 relay agent (with -6 argument). To see the usage message, issue the command dhcrelay -h.

14.3.1. Configure dhcrelay as a DHCPv4 and BOOTP relay agent

To run dhcrelay in DHCPv4 and BOOTP mode specify the servers to which the requests should be forwarded to. Copy and then edit the dhcrelay.service file as the root user: 
~]# cp /lib/systemd/system/dhcrelay.service /etc/systemd/system/
~]# vi /etc/systemd/system/dhcrelay.service
Edit the ExecStart option under section [Service] and add one or more server IPv4 addresses to the end of the line, for example: 
ExecStart=/usr/sbin/dhcrelay -d --no-pid 192.168.1.1
If you also want to specify interfaces where the DHCP Relay Agent listens for DHCP requests, add them to the ExecStart option with -i argument (otherwise it will listen on all interfaces), for example: 
ExecStart=/usr/sbin/dhcrelay -d --no-pid 192.168.1.1 -i em1
For other options see the dhcrelay(8) man page.
To activate the changes made, as the root user, restart the service: 
~]# systemctl --system daemon-reload
~]# systemctl restart dhcrelay

14.3.2. Configure dhcrelay as a DHCPv6 relay agent

To run dhcrelay in DHCPv6 mode add the -6 argument and specify the “lower interface” (on which queries will be received from clients or from other relay agents) and the “upper interface” (to which queries from clients and other relay agents should be forwarded). Copy dhcrelay.service to dhcrelay6.service and edit it as the root user: 
~]# cp /lib/systemd/system/dhcrelay.service /etc/systemd/system/dhcrelay6.service
~]# vi /etc/systemd/system/dhcrelay6.service
Edit the ExecStart option under section [Service] add -6 argument and add the “lower interface” and “upper interface” interface, for example: 
ExecStart=/usr/sbin/dhcrelay -d --no-pid -6 -l em1 -u em2
For other options see the dhcrelay(8) man page.
To activate the changes made, as the root user, restart the service: 
~]# systemctl --system daemon-reload
~]# systemctl restart dhcrelay6

14.4. Configuring a Multihomed DHCP Server

A multihomed DHCP server serves multiple networks, that is, multiple subnets. The examples in these sections detail how to configure a DHCP server to serve multiple networks, select which network interfaces to listen on, and how to define network settings for systems that move networks.
Before making any changes, back up the existing /etc/dhcp/dhcpd.conf file.
The DHCP daemon will only listen on interfaces for which it finds a subnet declaration in the /etc/dhcp/dhcpd.conf file.
The following is a basic /etc/dhcp/dhcpd.conf file, for a server that has two network interfaces, enp1s0 in a 10.0.0.0/24 network, and enp2s0 in a 172.16.0.0/24 network. Multiple subnet declarations allow you to define different settings for multiple networks: 
default-lease-time 600;
max-lease-time 7200;
subnet 10.0.0.0 netmask 255.255.255.0 {
	option subnet-mask 255.255.255.0;
	option routers 10.0.0.1;
	range 10.0.0.5 10.0.0.15;
}
subnet 172.16.0.0 netmask 255.255.255.0 {
	option subnet-mask 255.255.255.0;
	option routers 172.16.0.1;
	range 172.16.0.5 172.16.0.15;
}
subnet 10.0.0.0 netmask 255.255.255.0;
A subnet declaration is required for every network your DHCP server is serving. Multiple subnets require multiple subnet declarations. If the DHCP server does not have a network interface in a range of a subnet declaration, the DHCP server does not serve that network.
If there is only one subnet declaration, and no network interfaces are in the range of that subnet, the DHCP daemon fails to start, and an error such as the following is logged to /var/log/messages: 
dhcpd: No subnet declaration for enp1s0 (0.0.0.0).
dhcpd: ** Ignoring requests on enp1s0.  If this is not what
dhcpd:    you want, please write a subnet declaration
dhcpd:    in your dhcpd.conf file for the network segment
dhcpd:    to which interface enp2s0 is attached. **
dhcpd:
dhcpd:
dhcpd: Not configured to listen on any interfaces!
option subnet-mask 255.255.255.0;
The option subnet-mask option defines a subnet mask, and overrides the netmask value in the subnet declaration. In simple cases, the subnet and netmask values are the same.
option routers 10.0.0.1;
The option routers option defines the default gateway for the subnet. This is required for systems to reach internal networks on a different subnet, as well as external networks.
range 10.0.0.5 10.0.0.15;
The range option specifies the pool of available IP addresses. Systems are assigned an address from the range of specified IP addresses.
For further information, see the dhcpd.conf(5) man page.

Warning

To avoid misconfiguration when DHCP server gives IP addresses from one IP range to another physical Ethernet segment, make sure you do not enclose more subnets in a shared-network declaration.

14.4.1. Host Configuration

Before making any changes, back up the existing /etc/sysconfig/dhcpd and /etc/dhcp/dhcpd.conf files.
Configuring a Single System for Multiple Networks

The following /etc/dhcp/dhcpd.conf example creates two subnets, and configures an IP address for the same system, depending on which network it connects to: 

default-lease-time 600;
max-lease-time 7200;
subnet 10.0.0.0 netmask 255.255.255.0 {
	option subnet-mask 255.255.255.0;
	option routers 10.0.0.1;
	range 10.0.0.5 10.0.0.15;
}
subnet 172.16.0.0 netmask 255.255.255.0 {
	option subnet-mask 255.255.255.0;
	option routers 172.16.0.1;
	range 172.16.0.5 172.16.0.15;
}
host example0 {
	hardware ethernet 00:1A:6B:6A:2E:0B;
	fixed-address 10.0.0.20;
}
host example1 {
	hardware ethernet 00:1A:6B:6A:2E:0B;
	fixed-address 172.16.0.20;
}
host example0
The host declaration defines specific parameters for a single system, such as an IP address. To configure specific parameters for multiple hosts, use multiple host declarations.
Most DHCP clients ignore the name in host declarations, and as such, this name can be anything, as long as it is unique to other host declarations. To configure the same system for multiple networks, use a different name for each host declaration, otherwise the DHCP daemon fails to start. Systems are identified by the hardware ethernet option, not the name in the host declaration.
hardware ethernet 00:1A:6B:6A:2E:0B;
The hardware ethernet option identifies the system. To find this address, run the ip link command.
fixed-address 10.0.0.20;
The fixed-address option assigns a valid IP address to the system specified by the hardware ethernet option. This address must be outside the IP address pool specified with the range option.
If option statements do not end with a semicolon, the DHCP daemon fails to start, and an error such as the following is logged to /var/log/messages: 
/etc/dhcp/dhcpd.conf line 20: semicolon expected.
dhcpd: }
dhcpd: ^
dhcpd: /etc/dhcp/dhcpd.conf line 38: unexpected end of file
dhcpd:
dhcpd: ^
dhcpd: Configuration file errors encountered -- exiting
Configuring Systems with Multiple Network Interfaces

The following host declarations configure a single system, which has multiple network interfaces, so that each interface receives the same IP address. This configuration will not work if both network interfaces are connected to the same network at the same time: 

host interface0 {
	hardware ethernet 00:1a:6b:6a:2e:0b;
	fixed-address 10.0.0.18;
}
host interface1 {
	hardware ethernet 00:1A:6B:6A:27:3A;
	fixed-address 10.0.0.18;
}
For this example, interface0 is the first network interface, and interface1 is the second interface. The different hardware ethernet options identify each interface.
If such a system connects to another network, add more host declarations, remembering to:
  • assign a valid fixed-address for the network the host is connecting to.
  • make the name in the host declaration unique.
When a name given in a host declaration is not unique, the DHCP daemon fails to start, and an error such as the following is logged to /var/log/messages: 
dhcpd: /etc/dhcp/dhcpd.conf line 31: host interface0: already exists
dhcpd: }
dhcpd: ^
dhcpd: Configuration file errors encountered -- exiting
This error was caused by having multiple host interface0 declarations defined in /etc/dhcp/dhcpd.conf.

14.5. DHCP for IPv6 (DHCPv6)

The ISC DHCP includes support for IPv6 (DHCPv6) since the 4.x release with a DHCPv6 server, client, and relay agent functionality. The agents support both IPv4 and IPv6, however the agents can only manage one protocol at a time; for dual support they must be started separately for IPv4 and IPv6. For example, configure both DHCPv4 and DHCPv6 by editing their respective configuration files /etc/dhcp/dhcpd.conf and /etc/dhcp/dhcpd6.conf and then issue the following commands: 
~]# systemctl start dhcpd
~]# systemctl start dhcpd6
The DHCPv6 server configuration file can be found at /etc/dhcp/dhcpd6.conf.
The example server configuration file can be found at /usr/share/doc/dhcp-version/dhcpd6.conf.example.
A simple DHCPv6 server configuration file can look like this: 
subnet6 2001:db8:0:1::/64 {
        range6 2001:db8:0:1::129 2001:db8:0:1::254;
        option dhcp6.name-servers fec0:0:0:1::1;
        option dhcp6.domain-search "domain.example";
}
To assign a fixed-address to a client, based on the MAC address of the network interface card, use the hardware ethernet parameter: 
host otherclient {
        hardware ethernet 01:00:80:a2:55:67;
        fixed-address6 3ffe:501:ffff:100::4321;
 }
The configuration options in the shared-network, and group declaration for IPv6 are the same as IPV4. For more details, see the examples as demonstrated in Example 14.5, “Shared-network Declaration”, and Example 14.6, “Group Declaration”.

14.6. Configuring the radvd daemon for IPv6 routers

The router advertisement daemon (radvd) sends router advertisement messages which are required for IPv6 stateless autoconfiguration. This allows users to automatically configure their addresses, settings, routes and choose a default router based on these advertisements. To configure the radvd daemon:
  1. Install the radvd daemon: 
    ~]# sudo yum install radvd
  2. Set up the /etc/radvd.conf file. For example: 
    interface enp1s0
{
AdvSendAdvert on;
MinRtrAdvInterval 30;
MaxRtrAdvInterval 100;
prefix 2001:db8:1:0::/64
{
AdvOnLink on;
AdvAutonomous on;
AdvRouterAddr off;
};

};

    Note

    If you want to additionally advertise DNS resolvers along with the router advertisements, add the RDNSS <ip> <ip> <ip> { }; option in the /etc/radvd.conf file. To configure a DHCPv6 service for your subnets, you can set the AdvManagedFlag to on, so the router advertisements allow clients to automatically obtain an IPv6 address when a DHCPv6 service is available. For more details on configuring the DHCPv6 service, see Section 14.5, “DHCP for IPv6 (DHCPv6)”
  3. Enable the radvd daemon: 
    ~]# sudo systemctl enable radvd.service
  4. Start the radvd daemon immediately: 
    ~]# sudo systemctl start radvd.service
To display the content of router advertisement packages and the configured values sent by the radvd daemon, use the radvdump command: 
~]# radvdump
Router advertisement from fe80::280:c8ff:feb9:cef9 (hoplimit 255)
        AdvCurHopLimit: 64
        AdvManagedFlag: off
        AdvOtherConfigFlag: off
        AdvHomeAgentFlag: off
        AdvReachableTime: 0
        AdvRetransTimer: 0
        Prefix 2002:0102:0304:f101::/64
                AdvValidLifetime: 30
                AdvPreferredLifetime: 20
                AdvOnLink: off
                AdvAutonomous: on
                AdvRouterAddr: on
        Prefix 2001:0db8:100:f101::/64
                AdvValidLifetime: 2592000
                AdvPreferredLifetime: 604800
                AdvOnLink: on
                AdvAutonomous: on
                AdvRouterAddr: on
        AdvSourceLLAddress: 00 80 12 34 56 78
For more information on the radvd daemon, see the radvd(8), radvd.conf(5), radvdump(8) man pages.

14.7. Comparison of DHCPv6 to radvd

Dynamic Host configuration for IPv4 is mainly applied with DHCPv4. However, for IPv6 the following options are available:
  • Manually
  • Using the radvd daemon
  • Using the DHCPv6 server

Manually

Manual addressing is always available. You can assign IPv6 addresses to a system using the tools described in Section 3.3.6, “Connecting to a Network Using nmcli”, Section 7.2, “Configure Bonding Using the Text User Interface, nmtui”, Section 3.6, “Configuring IP Networking with ip Commands”.

Using the radvd Daemon

A standards-compliant IPv6 network must provide router advertisements, thus IPv6 configuration options can be applied running the router advertisement daemon (radvd). The router advertisements provide the on-link information on which prefix is actually available locally on a physical LAN. On top of router advertisements, you can select either manual IPv6 configuration, automatic IPv6 configuration through router advertisements or the Dynamic Host Configuration Protocol (DHCPv6). For more details on configuring the radvd daemon, see Section 14.6, “Configuring the radvd daemon for IPv6 routers”.

Using the DHCPv6 Server

When address management is under central administration, the user can set up a DHCPv6 server. The availability of DHCPv6 is announced by flags in the router advertisement packets.
Table 14.1. Comparison of DHCPv6 to radvd
DHCPv6 radvd
Guarantee random addresses to protect privacy. Provide information on a default gateway.
Send further network configuration options to clients. For example, Network Time Protocol (NTP) servers, Session Initiation Protocol (SIP) servers, Preboot Execution Environment (iPXE) configuration.  
Map MAC addresses to IPv6 addresses.  

Note

To correctly configure a network, use DHCPv6 in conjunction with radvd, as only router advertisements provide information on a default gateway.

14.8. Additional Resources

  • dhcpd(8) man page — Describes how the DHCP daemon works.
  • dhcpd.conf(5) man page — Explains how to configure the DHCP configuration file; includes some examples.
  • dhcpd.leases(5) man page — Describes a persistent database of leases.
  • dhcp-options(5) man page — Explains the syntax for declaring DHCP options in dhcpd.conf; includes some examples.
  • dhcrelay(8) man page — Explains the DHCP Relay Agent and its configuration options.
  • /usr/share/doc/dhcp-version/ — Contains example files, README files, and release notes for current versions of the DHCP service.

Chapter 15. DNS Servers

DNS (Domain Name System), is a distributed database system that is used to associate host names with their respective IP addresses. For users, this has the advantage that they can refer to machines on the network by names that are usually easier to remember than the numerical network addresses. For system administrators, using a DNS server, also known as a name server, enables changing the IP address for a host without ever affecting the name-based queries. The use of the DNS databases is not only for resolving IP addresses to domain names and their use is becoming broader and broader as DNSSEC is deployed.

15.1. Introduction to DNS

DNS is usually implemented using one or more centralized servers that are authoritative for certain domains. When a client host requests information from a name server, it usually connects to port 53. The name server then attempts to resolve the name requested. If the name server is configured to be a recursive name servers and it does not have an authoritative answer, or does not already have the answer cached from an earlier query, it queries other name servers, called root name servers, to determine which name servers are authoritative for the name in question, and then queries them to get the requested name. Name servers configured as purely authoritative, with recursion disabled, will not do lookups on behalf of clients.

15.1.1. Name server Zones

In a DNS server, all information is stored in basic data elements called resource records (RR). Resource records are defined in RFC 1034. The domain names are organized into a tree structure. Each level of the hierarchy is divided by a period (.). For example: The root domain, denoted by ., is the root of the DNS tree, which is at level zero. The domain name com, referred to as the top-level domain (TLD) is a child of the root domain (.) so it is the first level of the hierarchy. The domain name example.com is at the second level of the hierarchy.

Example 15.1. A Simple Resource Record

An example of a simple resource record (RR): 
example.com.      86400    IN         A           192.0.2.1
The domain name, example.com, is the owner for the RR. The value 86400 is the time to live (TTL). The letters IN, meaning “the Internet system”, indicate the class of the RR. The letter A indicates the type of RR (in this example, a host address). The host address 192.0.2.1 is the data contained in the final section of this RR. This one line example is a RR. A set of RRs with the same type, owner, and class is called a resource record set (RRSet).
Zones are defined on authoritative name servers through the use of zone files, which contain definitions of the resource records in each zone. Zone files are stored on primary name servers (also called master name servers), where changes are made to the files, and secondary name servers (also called slave name servers), which receive zone definitions from the primary name servers. Both primary and secondary name servers are authoritative for the zone and look the same to clients. Depending on the configuration, any name server can also serve as a primary or secondary server for multiple zones at the same time.
Note that administrators of DNS and DHCP servers, as well as any provisioning applications, should agree on the host name format used in an organization. See Section 6.1.1, “Recommended Naming Practices” for more information on the format of host names.

15.1.2. Name server Types

There are two name server configuration types:
authoritative
Authoritative name servers answer to resource records that are part of their zones only. This category includes both primary (master) and secondary (slave) name servers.
recursive
Recursive name servers offer resolution services, but they are not authoritative for any zone. Answers for all resolutions are cached in a memory for a fixed period of time, which is specified by the retrieved resource record.
Although a name server can be both authoritative and recursive at the same time, it is recommended not to combine the configuration types. To be able to perform their work, authoritative servers should be available to all clients all the time. On the other hand, since the recursive lookup takes far more time than authoritative responses, recursive servers should be available to a restricted number of clients only, otherwise they are prone to distributed denial of service (DDoS) attacks.

15.1.3. BIND as a Name server

BIND consists of a set of DNS-related programs. It contains a name server called named, an administration utility called rndc, and a debugging tool called dig. See Red Hat Enterprise Linux System Administrator's Guide for more information on how to run a service in Red Hat Enterprise Linux.

15.2. BIND

This section covers BIND (Berkeley Internet Name Domain), the DNS server included in Red Hat Enterprise Linux. It focuses on the structure of its configuration files, and describes how to administer it both locally and remotely.

15.2.1. Empty Zones

BIND configures a number of “empty zones” to prevent recursive servers from sending unnecessary queries to Internet servers that cannot handle them (thus creating delays and SERVFAIL responses to clients who query for them). These empty zones ensure that immediate and authoritative NXDOMAIN responses are returned instead. The configuration option empty-zones-enable controls whether or not empty zones are created, whilst the option disable-empty-zone can be used in addition to disable one or more empty zones from the list of default prefixes that would be used.
The number of empty zones created for RFC 1918 prefixes has been increased, and users of BIND 9.9 and above will see the RFC 1918 empty zones both when empty-zones-enable is unspecified (defaults to yes), and when it is explicitly set to yes.

15.2.2. Configuring the named Service

When the named service is started, it reads the configuration from the files as described in Table 15.1, “The named Service Configuration Files”.
Table 15.1. The named Service Configuration Files
Path Description
/etc/named.conf The main configuration file.
/etc/named/ An auxiliary directory for configuration files that are included in the main configuration file.
The configuration file consists of a collection of statements with nested options surrounded by opening and closing curly brackets ({ and }). Note that when editing the file, you have to be careful not to make any syntax error, otherwise the named service will not start. A typical /etc/named.conf file is organized as follows: 
statement-1 ["statement-1-name"] [statement-1-class] {
  option-1;
  option-2;
  option-N;
};
statement-2 ["statement-2-name"] [statement-2-class] {
  option-1;
  option-2;
  option-N;
};
statement-N ["statement-N-name"] [statement-N-class] {
  option-1;
  option-2;
  option-N;
};

Note

If you have installed the bind-chroot package, the BIND service will run in the chroot environment. In that case, the initialization script will mount the above configuration files using the mount --bind command, so that you can manage the configuration outside this environment. There is no need to copy anything into the /var/named/chroot/ directory because it is mounted automatically. This simplifies maintenance since you do not need to take any special care of BIND configuration files if it is run in a chroot environment. You can organize everything as you would with BIND not running in a chroot environment.
The following directories are automatically mounted into the /var/named/chroot/ directory if the corresponding mount point directories underneath /var/named/chroot/ are empty:
  • /etc/named
  • /etc/pki/dnssec-keys
  • /run/named
  • /var/named
  • /usr/lib64/bind or /usr/lib/bind (architecture dependent).
The following files are also mounted if the target file does not exist in /var/named/chroot/:
  • /etc/named.conf
  • /etc/rndc.conf
  • /etc/rndc.key
  • /etc/named.rfc1912.zones
  • /etc/named.dnssec.keys
  • /etc/named.iscdlv.key
  • /etc/named.root.key

Important

Editing files which have been mounted in a chroot environment requires creating a backup copy and then editing the original file. Alternatively, use an editor with “edit-a-copy” mode disabled. For example, to edit the BIND's configuration file, /etc/named.conf, with Vim while it is running in a chroot environment, issue the following command as root: 
~]# vim -c "set backupcopy=yes" /etc/named.conf
15.2.2.1. Installing BIND in a chroot Environment
To install BIND to run in a chroot environment, issue the following command as root: 
~]# yum install bind-chroot
To enable the named-chroot service, first check if the named service is running by issuing the following command: 
~]$ systemctl status named
If it is running, it must be disabled.
To disable named, issue the following commands as root: 
~]# systemctl stop named
~]# systemctl disable named
Then, to enable the named-chroot service, issue the following commands as root: 
~]# systemctl enable named-chroot
~]# systemctl start named-chroot
To check the status of the named-chroot service, issue the following command as root: 
~]# systemctl status named-chroot
15.2.2.2. Common Statement Types
The following types of statements are commonly used in /etc/named.conf:
acl
The acl (Access Control List) statement allows you to define groups of hosts, so that they can be permitted or denied access to the nameserver. It takes the following form: 
acl acl-name {
  match-element;
  ...
};
The acl-name statement name is the name of the access control list, and the match-element option is usually an individual IP address (such as 10.0.1.1) or a Classless Inter-Domain Routing (CIDR) network notation (for example, 10.0.1.0/24). For a list of already defined keywords, see Table 15.2, “Predefined Access Control Lists”.
Table 15.2. Predefined Access Control Lists
Keyword Description
any Matches every IP address.
localhost Matches any IP address that is in use by the local system.
localnets Matches any IP address on any network to which the local system is connected.
none Does not match any IP address.
The acl statement can be especially useful in conjunction with other statements such as options. Example 15.2, “Using acl in Conjunction with Options” defines two access control lists, black-hats and red-hats, and adds black-hats on the blacklist while granting red-hats normal access.

Example 15.2. Using acl in Conjunction with Options

acl black-hats {
  10.0.2.0/24;
  192.168.0.0/24;
  1234:5678::9abc/24;
};
acl red-hats {
  10.0.1.0/24;
};
options {
  blackhole { black-hats; };
  allow-query { red-hats; };
  allow-query-cache { red-hats; };
};
include
The include statement allows you to include files in the /etc/named.conf, so that potentially sensitive data can be placed in a separate file with restricted permissions. It takes the following form: 
include "file-name"
The file-name statement name is an absolute path to a file.

Example 15.3. Including a File to /etc/named.conf

include "/etc/named.rfc1912.zones";
options
The options statement allows you to define global server configuration options as well as to set defaults for other statements. It can be used to specify the location of the named working directory, the types of queries allowed, and much more. It takes the following form: 
options {
  option;
  ...
};
For a list of frequently used option directives, see Table 15.3, “Commonly Used Configuration Options” below.
Table 15.3. Commonly Used Configuration Options
Option Description
allow-query Specifies which hosts are allowed to query the nameserver for authoritative resource records. It accepts an access control list, a collection of IP addresses, or networks in the CIDR notation. All hosts are allowed by default.
allow-query-cache Specifies which hosts are allowed to query the nameserver for non-authoritative data such as recursive queries. Only localhost and localnets are allowed by default.
blackhole Specifies which hosts are not allowed to query the nameserver. This option should be used when a particular host or network floods the server with requests. The default option is none.
directory Specifies a working directory for the named service. The default option is /var/named/.
disable-empty-zone Used to disable one or more empty zones from the list of default prefixes that would be used. Can be specified in the options statement and also in view statements. It can be used multiple times.
dnssec-enable Specifies whether to return DNSSEC related resource records. The default option is yes.
dnssec-validation Specifies whether to prove that resource records are authentic through DNSSEC. The default option is yes.
empty-zones-enable Controls whether or not empty zones are created. Can be specified only in the options statement.
forwarders Specifies a list of valid IP addresses for nameservers to which the requests should be forwarded for resolution.
forward
Specifies the behavior of the forwarders directive. It accepts the following options:
  • first — The server will query the nameservers listed in the forwarders directive before attempting to resolve the name on its own.
  • only — When unable to query the nameservers listed in the forwarders directive, the server will not attempt to resolve the name on its own.
listen-on Specifies the IPv4 network interface on which to listen for queries. On a DNS server that also acts as a gateway, you can use this option to answer queries originating from a single network only. All IPv4 interfaces are used by default.
listen-on-v6 Specifies the IPv6 network interface on which to listen for queries. On a DNS server that also acts as a gateway, you can use this option to answer queries originating from a single network only. All IPv6 interfaces are used by default.
max-cache-size Specifies the maximum amount of memory to be used for server caches. When the limit is reached, the server causes records to expire prematurely so that the limit is not exceeded. In a server with multiple views, the limit applies separately to the cache of each view. The default option is 32M.
notify
Specifies whether to notify the secondary nameservers when a zone is updated. It accepts the following options:
  • yes — The server will notify all secondary nameservers.
  • no — The server will not notify any secondary nameserver.
  • master-only — The server will notify primary server for the zone only.
  • explicit — The server will notify only the secondary servers that are specified in the also-notify list within a zone statement.
pid-file Specifies the location of the process ID file created by the named service.
recursion Specifies whether to act as a recursive server. The default option is yes.
statistics-file Specifies an alternate location for statistics files. The /var/named/named.stats file is used by default.

Note

The directory used by named for runtime data has been moved from the BIND default location, /var/run/named/, to a new location /run/named/. As a result, the PID file has been moved from the default location /var/run/named/named.pid to the new location /run/named/named.pid. In addition, the session-key file has been moved to /run/named/session.key. These locations need to be specified by statements in the options section. See Example 15.4, “Using the options Statement”.

Important

To prevent distributed denial of service (DDoS) attacks, it is recommended that you use the allow-query-cache option to restrict recursive DNS services for a particular subset of clients only.
See the BIND 9 Administrator Reference Manual referenced in Section 15.2.8.1, “Installed Documentation”, and the named.conf manual page for a complete list of available options.

Example 15.4. Using the options Statement

options {
  allow-query       { localhost; };
  listen-on port    53 { 127.0.0.1; };
  listen-on-v6 port 53 { ::1; };
  max-cache-size    256M;
  directory         "/var/named";
  statistics-file   "/var/named/data/named_stats.txt";

  recursion         yes;
  dnssec-enable     yes;
  dnssec-validation yes;

  pid-file          "/run/named/named.pid";
  session-keyfile   "/run/named/session.key";
};
zone
The zone statement allows you to define the characteristics of a zone, such as the location of its configuration file and zone-specific options, and can be used to override the global options statements. It takes the following form: 
zone zone-name [zone-class] {
  option;
  ...
};
The zone-name attribute is the name of the zone, zone-class is the optional class of the zone, and option is a zone statement option as described in Table 15.4, “Commonly Used Options in Zone Statements”.
The zone-name attribute is particularly important, as it is the default value assigned for the $ORIGIN directive used within the corresponding zone file located in the /var/named/ directory. The named daemon appends the name of the zone to any non-fully qualified domain name listed in the zone file. For example, if a zone statement defines the namespace for example.com, use example.com as the zone-name so that it is placed at the end of host names within the example.com zone file.
For more information about zone files, see Section 15.2.3, “Editing Zone Files”.
Table 15.4. Commonly Used Options in Zone Statements
Option Description
allow-query Specifies which clients are allowed to request information about this zone. This option overrides global allow-query option. All query requests are allowed by default.
allow-transfer Specifies which secondary servers are allowed to request a transfer of the zone's information. All transfer requests are allowed by default.
allow-update
Specifies which hosts are allowed to dynamically update information in their zone. The default option is to deny all dynamic update requests.
Note that you should be careful when allowing hosts to update information about their zone. Do not set IP addresses in this option unless the server is in the trusted network. Instead, use TSIG key as described in Section 15.2.6.3, “Transaction SIGnatures (TSIG)”.
file Specifies the name of the file in the named working directory that contains the zone's configuration data.
masters Specifies from which IP addresses to request authoritative zone information. This option is used only if the zone is defined as type slave.
notify
Specifies whether to notify the secondary nameservers when a zone is updated. It accepts the following options:
  • yes — The server will notify all secondary nameservers.
  • no — The server will not notify any secondary nameserver.
  • master-only — The server will notify primary server for the zone only.
  • explicit — The server will notify only the secondary servers that are specified in the also-notify list within a zone statement.
type
Specifies the zone type. It accepts the following options:
  • delegation-only — Enforces the delegation status of infrastructure zones such as COM, NET, or ORG. Any answer that is received without an explicit or implicit delegation is treated as NXDOMAIN. This option is only applicable in TLDs (Top-Level Domain) or root zone files used in recursive or caching implementations.
  • forward — Forwards all requests for information about this zone to other nameservers.
  • hint — A special type of zone used to point to the root nameservers which resolve queries when a zone is not otherwise known. No configuration beyond the default is necessary with a hint zone.
  • master — Designates the nameserver as authoritative for this zone. A zone should be set as the master if the zone's configuration files reside on the system.
  • slave — Designates the nameserver as a secondary server for this zone. Primary server is specified in the masters directive.
Most changes to the /etc/named.conf file of a primary or secondary nameserver involve adding, modifying, or deleting zone statements, and only a small subset of zone statement options is usually needed for a nameserver to work efficiently.
In Example 15.5, “A Zone Statement for a Primary nameserver”, the zone is identified as example.com, the type is set to master, and the named service is instructed to read the /var/named/example.com.zone file. It also allows only a secondary nameserver (192.168.0.2) to transfer the zone.

Example 15.5. A Zone Statement for a Primary nameserver

zone "example.com" IN {
  type master;
  file "example.com.zone";
  allow-transfer { 192.168.0.2; };
};
A secondary server's zone statement is slightly different. The type is set to slave, and the masters directive is telling named the IP address of the primary server.
In Example 15.6, “A Zone Statement for a Secondary nameserver”, the named service is configured to query the primary server at the 192.168.0.1 IP address for information about the example.com zone. The received information is then saved to the /var/named/slaves/example.com.zone file. Note that you have to put all secondary zones in the /var/named/slaves/ directory, otherwise the service will fail to transfer the zone.

Example 15.6. A Zone Statement for a Secondary nameserver

zone "example.com" {
  type slave;
  file "slaves/example.com.zone";
  masters { 192.168.0.1; };
};
15.2.2.3. Other Statement Types
The following types of statements are less commonly used in /etc/named.conf:
controls
The controls statement allows you to configure various security requirements necessary to use the rndc command to administer the named service.
See Section 15.2.4, “Using the rndc Utility” for more information on the rndc utility and its usage.
key
The key statement allows you to define a particular key by name. Keys are used to authenticate various actions, such as secure updates or the use of the rndc command. Two options are used with key:
  • algorithm algorithm-name — The type of algorithm to be used (for example, hmac-md5).
  • secret "key-value" — The encrypted key.
See Section 15.2.4, “Using the rndc Utility” for more information on the rndc utility and its usage.
logging
The logging statement allows you to use multiple types of logs, so called channels. By using the channel option within the statement, you can construct a customized type of log with its own file name (file), size limit (size), version number (version), and level of importance (severity). Once a customized channel is defined, a category option is used to categorize the channel and begin logging when the named service is restarted.
By default, named sends standard messages to the rsyslog daemon, which places them in /var/log/messages. Several standard channels are built into BIND with various severity levels, such as default_syslog (which handles informational logging messages) and default_debug (which specifically handles debugging messages). A default category, called default, uses the built-in channels to do normal logging without any special configuration.
Customizing the logging process can be a very detailed process and is beyond the scope of this chapter. For information on creating custom BIND logs, see the BIND 9 Administrator Reference Manual referenced in Section 15.2.8.1, “Installed Documentation”.
server
The server statement allows you to specify options that affect how the named service should respond to remote nameservers, especially with regard to notifications and zone transfers.
The transfer-format option controls the number of resource records that are sent with each message. It can be either one-answer (only one resource record), or many-answers (multiple resource records). Note that while the many-answers option is more efficient, it is not supported by older versions of BIND.
trusted-keys
The trusted-keys statement allows you to specify assorted public keys used for secure DNS (DNSSEC). See Section 15.2.6.4, “DNS Security Extensions (DNSSEC)” for more information on this topic.
view
The view statement allows you to create special views depending upon which network the host querying the nameserver is on. This allows some hosts to receive one answer regarding a zone while other hosts receive totally different information. Alternatively, certain zones may only be made available to particular trusted hosts while non-trusted hosts can only make queries for other zones.
Multiple views can be used as long as their names are unique. The match-clients option allows you to specify the IP addresses that apply to a particular view. If the options statement is used within a view, it overrides the already configured global options. Finally, most view statements contain multiple zone statements that apply to the match-clients list.
Note that the order in which the view statements are listed is important, as the first statement that matches a particular client's IP address is used. For more information on this topic, see Section 15.2.6.1, “Multiple Views”.
15.2.2.4. Comment Tags
Additionally to statements, the /etc/named.conf file can also contain comments. Comments are ignored by the named service, but can prove useful when providing additional information to a user. The following are valid comment tags:
//
Any text after the // characters to the end of the line is considered a comment. For example: 
notify yes;  // notify all secondary nameservers
#
Any text after the # character to the end of the line is considered a comment. For example: 
notify yes;  # notify all secondary nameservers
/* and */
Any block of text enclosed in /* and */ is considered a comment. For example: 
notify yes;  /* notify all secondary nameservers */

15.2.3. Editing Zone Files

As outlined in Section 15.1.1, “Name server Zones”, zone files contain information about a namespace. They are stored in the named working directory located in /var/named/ by default. Each zone file is named according to the file option in the zone statement, usually in a way that relates to the domain in and identifies the file as containing zone data, such as example.com.zone.
Table 15.5. The named Service Zone Files
Path Description
/var/named/ The working directory for the named service. The nameserver is not allowed to write to this directory.
/var/named/slaves/ The directory for secondary zones. This directory is writable by the named service.
/var/named/dynamic/ The directory for other files, such as dynamic DNS (DDNS) zones or managed DNSSEC keys. This directory is writable by the named service.
/var/named/data/ The directory for various statistics and debugging files. This directory is writable by the named service.
A zone file consists of directives and resource records. Directives tell the nameserver to perform tasks or apply special settings to the zone, resource records define the parameters of the zone and assign identities to individual hosts. While the directives are optional, the resource records are required in order to provide name service to a zone.
All directives and resource records should be entered on individual lines.
15.2.3.1. Common Directives
Directives begin with the dollar sign character ($) followed by the name of the directive, and usually appear at the top of the file. The following directives are commonly used in zone files:
$INCLUDE
The $INCLUDE directive allows you to include another file at the place where it appears, so that other zone settings can be stored in a separate zone file.

Example 15.7. Using the $INCLUDE Directive

$INCLUDE /var/named/penguin.example.com
$ORIGIN
The $ORIGIN directive allows you to append the domain name to unqualified records, such as those with the host name only. Note that the use of this directive is not necessary if the zone is specified in /etc/named.conf, since the zone name is used by default.
In Example 15.8, “Using the $ORIGIN Directive”, any names used in resource records that do not end in a trailing period (the . character) are appended with example.com.

Example 15.8. Using the $ORIGIN Directive

$ORIGIN example.com.
$TTL
The $TTL directive allows you to set the default Time to Live (TTL) value for the zone, that is, how long is a zone record valid. Each resource record can contain its own TTL value, which overrides this directive.
Increasing this value allows remote nameservers to cache the zone information for a longer period of time, reducing the number of queries for the zone and lengthening the amount of time required to propagate resource record changes.

Example 15.9. Using the $TTL Directive

$TTL 1D
15.2.3.2. Common Resource Records
The following resource records are commonly used in zone files:
A
The Address record specifies an IP address to be assigned to a name. It takes the following form: 
hostname IN A IP-address
If the hostname value is omitted, the record will point to the last specified hostname.
In Example 15.10, “Using the A Resource Record”, the requests for server1.example.com are pointed to 10.0.1.3 or 10.0.1.5.

Example 15.10. Using the A Resource Record

server1  IN  A  10.0.1.3
         IN  A  10.0.1.5
CNAME
The Canonical Name record maps one name to another. Because of this, this type of record is sometimes referred to as an alias record. It takes the following form: 
alias-name IN CNAME real-name
CNAME records are most commonly used to point to services that use a common naming scheme, such as www for Web servers. However, there are multiple restrictions for their usage:
  • CNAME records should not point to other CNAME records. This is mainly to avoid possible infinite loops.
  • CNAME records should not contain other resource record types (such as A, NS, MX, and so on). The only exception are DNSSEC related records (RRSIG, NSEC, and so on) when the zone is signed.
  • Other resource records that point to the fully qualified domain name (FQDN) of a host (NS, MX, PTR) should not point to a CNAME record.
In Example 15.11, “Using the CNAME Resource Record”, the A record binds a host name to an IP address, while the CNAME record points the commonly used www host name to it.

Example 15.11. Using the CNAME Resource Record

server1  IN  A      10.0.1.5
www      IN  CNAME  server1
MX
The Mail Exchange record specifies where the mail sent to a particular namespace controlled by this zone should go. It takes the following form: 
IN MX preference-value email-server-name
The email-server-name is a fully qualified domain name (FQDN). The preference-value allows numerical ranking of the email servers for a namespace, giving preference to some email systems over others. The MX resource record with the lowest preference-value is preferred over the others. However, multiple email servers can possess the same value to distribute email traffic evenly among them.
In Example 15.12, “Using the MX Resource Record”, the first mail.example.com email server is preferred to the mail2.example.com email server when receiving email destined for the example.com domain.

Example 15.12. Using the MX Resource Record

example.com.  IN  MX  10  mail.example.com.
              IN  MX  20  mail2.example.com.
NS
The Nameserver record announces authoritative nameservers for a particular zone. It takes the following form: 
IN NS nameserver-name
The nameserver-name should be a fully qualified domain name (FQDN). Note that when two nameservers are listed as authoritative for the domain, it is not important whether these nameservers are secondary nameservers, or if one of them is a primary server. They are both still considered authoritative.

Example 15.13. Using the NS Resource Record

IN  NS  dns1.example.com.
IN  NS  dns2.example.com.
PTR
The Pointer record points to another part of the namespace. It takes the following form: 
last-IP-digit IN PTR FQDN-of-system
The last-IP-digit directive is the last number in an IP address, and the FQDN-of-system is a fully qualified domain name (FQDN).
PTR records are primarily used for reverse name resolution, as they point IP addresses back to a particular name. See Section 15.2.3.4.2, “A Reverse Name Resolution Zone File” for examples of PTR records in use.
SOA
The Start of Authority record announces important authoritative information about a namespace to the nameserver. Located after the directives, it is the first resource record in a zone file. It takes the following form: 
@  IN  SOA  primary-name-server hostmaster-email (
       serial-number
       time-to-refresh
       time-to-retry
       time-to-expire
       minimum-TTL )
The directives are as follows:
  • The @ symbol places the $ORIGIN directive (or the zone's name if the $ORIGIN directive is not set) as the namespace being defined by this SOA resource record.
  • The primary-name-server directive is the host name of the primary nameserver that is authoritative for this domain.
  • The hostmaster-email directive is the email of the person to contact about the namespace.
  • The serial-number directive is a numerical value incremented every time the zone file is altered to indicate it is time for the named service to reload the zone.
  • The time-to-refresh directive is the numerical value secondary nameservers use to determine how long to wait before asking the primary nameserver if any changes have been made to the zone.
  • The time-to-retry directive is a numerical value used by secondary nameservers to determine the length of time to wait before issuing a refresh request in the event that the primary nameserver is not answering. If the primary server has not replied to a refresh request before the amount of time specified in the time-to-expire directive elapses, the secondary servers stop responding as an authority for requests concerning that namespace.
  • In BIND 4 and 8, the minimum-TTL directive is the amount of time other nameservers cache the zone's information. In BIND 9, it defines how long negative answers are cached for. Caching of negative answers can be set to a maximum of 3 hours (3H).
When configuring BIND, all times are specified in seconds. However, it is possible to use abbreviations when specifying units of time other than seconds, such as minutes (M), hours (H), days (D), and weeks (W). Table 15.6, “Seconds compared to other time units” shows an amount of time in seconds and the equivalent time in another format.
Table 15.6. Seconds compared to other time units
Seconds Other Time Units
60 1M
1800 30M
3600 1H
10800 3H
21600 6H
43200 12H
86400 1D
259200 3D
604800 1W
31536000 365D

Example 15.14. Using the SOA Resource Record

@  IN  SOA  dns1.example.com.  hostmaster.example.com. (
       2001062501  ; serial
       21600       ; refresh after 6 hours
       3600        ; retry after 1 hour
       604800      ; expire after 1 week
       86400 )     ; minimum TTL of 1 day
15.2.3.3. Comment Tags
Additionally to resource records and directives, a zone file can also contain comments. Comments are ignored by the named service, but can prove useful when providing additional information to the user. Any text after the semicolon character to the end of the line is considered a comment. For example: 
   604800  ; expire after 1 week
15.2.3.4. Example Usage
The following examples show the basic usage of zone files.
15.2.3.4.1. A Simple Zone File
Example 15.15, “A simple zone file” demonstrates the use of standard directives and SOA values.

Example 15.15. A simple zone file

$ORIGIN example.com.
$TTL 86400
@         IN  SOA  dns1.example.com.  hostmaster.example.com. (
              2001062501  ; serial
              21600       ; refresh after 6 hours
              3600        ; retry after 1 hour
              604800      ; expire after 1 week
              86400 )     ; minimum TTL of 1 day
;
;
          IN  NS     dns1.example.com.
          IN  NS     dns2.example.com.
dns1      IN  A      10.0.1.1
          IN  AAAA   aaaa:bbbb::1
dns2      IN  A      10.0.1.2
          IN  AAAA   aaaa:bbbb::2
;
;
@         IN  MX     10  mail.example.com.
          IN  MX     20  mail2.example.com.
mail      IN  A      10.0.1.5
          IN  AAAA   aaaa:bbbb::5
mail2     IN  A      10.0.1.6
          IN  AAAA   aaaa:bbbb::6
;
;
; This sample zone file illustrates sharing the same IP addresses
; for multiple services:
;
services  IN  A      10.0.1.10
          IN  AAAA   aaaa:bbbb::10
          IN  A      10.0.1.11
          IN  AAAA   aaaa:bbbb::11

ftp       IN  CNAME  services.example.com.
www       IN  CNAME  services.example.com.
;
;
In this example, the authoritative nameservers are set as dns1.example.com and dns2.example.com, and are tied to the 10.0.1.1 and 10.0.1.2 IP addresses respectively using the A record.
The email servers configured with the MX records point to mail and mail2 through A records. Since these names do not end in a trailing period, the $ORIGIN domain is placed after them, expanding them to mail.example.com and mail2.example.com.
Services available at the standard names, such as www.example.com (WWW), are pointed at the appropriate servers using the CNAME record.
This zone file would be called into service with a zone statement in the /etc/named.conf similar to the following: 
zone "example.com" IN {
  type master;
  file "example.com.zone";
  allow-update { none; };
};
15.2.3.4.2. A Reverse Name Resolution Zone File
A reverse name resolution zone file is used to translate an IP address in a particular namespace into a fully qualified domain name (FQDN). It looks very similar to a standard zone file, except that the PTR resource records are used to link the IP addresses to a fully qualified domain name as shown in Example 15.16, “A reverse name resolution zone file”.

Example 15.16. A reverse name resolution zone file

$ORIGIN 1.0.10.in-addr.arpa.
$TTL 86400
@  IN  SOA  dns1.example.com.  hostmaster.example.com. (
       2001062501  ; serial
       21600       ; refresh after 6 hours
       3600        ; retry after 1 hour
       604800      ; expire after 1 week
       86400 )     ; minimum TTL of 1 day
;
@  IN  NS   dns1.example.com.
;
1  IN  PTR  dns1.example.com.
2  IN  PTR  dns2.example.com.
;
5  IN  PTR  server1.example.com.
6  IN  PTR  server2.example.com.
;
3  IN  PTR  ftp.example.com.
4  IN  PTR  ftp.example.com.
In this example, IP addresses 10.0.1.1 through 10.0.1.6 are pointed to the corresponding fully qualified domain name.
This zone file would be called into service with a zone statement in the /etc/named.conf file similar to the following: 
zone "1.0.10.in-addr.arpa" IN {
  type master;
  file "example.com.rr.zone";
  allow-update { none; };
};
There is very little difference between this example and a standard zone statement, except for the zone name. Note that a reverse name resolution zone requires the first three blocks of the IP address reversed followed by .in-addr.arpa. This allows the single block of IP numbers used in the reverse name resolution zone file to be associated with the zone.

15.2.4. Using the rndc Utility

The rndc utility is a command-line tool that allows you to administer the named service, both locally and from a remote machine. Its usage is as follows: 
rndc [option...] command [command-option]
15.2.4.1. Configuring the Utility
To prevent unauthorized access to the service, named must be configured to listen on the selected port (953 by default), and an identical key must be used by both the service and the rndc utility.
Table 15.7. Relevant files
Path Description
/etc/named.conf The default configuration file for the named service.
/etc/rndc.conf The default configuration file for the rndc utility.
/etc/rndc.key The default key location.
The rndc configuration is located in /etc/rndc.conf. If the file does not exist, the utility will use the key located in /etc/rndc.key, which was generated automatically during the installation process using the rndc-confgen -a command.
The named service is configured using the controls statement in the /etc/named.conf configuration file as described in Section 15.2.2.3, “Other Statement Types”. Unless this statement is present, only the connections from the loopback address (127.0.0.1) will be allowed, and the key located in /etc/rndc.key will be used.
For more information on this topic, see manual pages and the BIND 9 Administrator Reference Manual listed in Section 15.2.8, “Additional Resources”.

Important

To prevent unprivileged users from sending control commands to the service, make sure only root is allowed to read the /etc/rndc.key file: 
~]# chmod o-rwx /etc/rndc.key
15.2.4.2. Checking the Service Status
To check the current status of the named service, use the following command: 
~]# rndc status
version: 9.7.0-P2-RedHat-9.7.0-5.P2.el6
CPUs found: 1
worker threads: 1
number of zones: 16
debug level: 0
xfers running: 0
xfers deferred: 0
soa queries in progress: 0
query logging is OFF
recursive clients: 0/0/1000
tcp clients: 0/100
server is up and running
15.2.4.3. Reloading the Configuration and Zones
To reload both the configuration file and zones, type the following at a shell prompt: 
~]# rndc reload
server reload successful
This will reload the zones while keeping all previously cached responses, so that you can make changes to the zone files without losing all stored name resolutions.
To reload a single zone, specify its name after the reload command, for example: 
~]# rndc reload localhost
zone reload up-to-date
Finally, to reload the configuration file and newly added zones only, type: 
~]# rndc reconfig

Note

If you intend to manually modify a zone that uses Dynamic DNS (DDNS), make sure you run the freeze command first: 
~]# rndc freeze localhost
Once you are finished, run the thaw command to allow the DDNS again and reload the zone: 
~]# rndc thaw localhost
The zone reload and thaw was successful.
15.2.4.4. Updating Zone Keys
To update the DNSSEC keys and sign the zone, use the sign command. For example: 
~]# rndc sign localhost
Note that to sign a zone with the above command, the auto-dnssec option has to be set to maintain in the zone statement. For example: 
zone "localhost" IN {
  type master;
  file "named.localhost";
  allow-update { none; };
  auto-dnssec maintain;
};
15.2.4.5. Enabling the DNSSEC Validation
To enable the DNSSEC validation, issue the following command as root: 
~]# rndc validation on
Similarly, to disable this option, type: 
~]# rndc validation off
See the options statement described in Section 15.2.2.2, “Common Statement Types” for information on how to configure this option in /etc/named.conf.
The Red Hat Enterprise Linux 7 Security Guide has a comprehensive section on DNSSEC.
15.2.4.6. Enabling the Query Logging
To enable (or disable in case it is currently enabled) the query logging, issue the following command as root: 
~]# rndc querylog
To check the current setting, use the status command as described in Section 15.2.4.2, “Checking the Service Status”.

15.2.5. Using the dig Utility

The dig utility is a command-line tool that allows you to perform DNS lookups and debug a nameserver configuration. Its typical usage is as follows: 
dig [@server] [option...] name type
See Section 15.2.3.2, “Common Resource Records” for a list of common values to use for type.
15.2.5.1. Looking Up a Nameserver
To look up a nameserver for a particular domain, use the command in the following form: 
dig name NS
In Example 15.17, “A sample nameserver lookup”, the dig utility is used to display nameservers for example.com.

Example 15.17. A sample nameserver lookup

~]$ dig example.com NS

; <<>> DiG 9.7.1-P2-RedHat-9.7.1-2.P2.fc13 <<>> example.com NS
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57883
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;example.com.                   IN      NS

;; ANSWER SECTION:
example.com.            99374   IN      NS      a.iana-servers.net.
example.com.            99374   IN      NS      b.iana-servers.net.

;; Query time: 1 msec
;; SERVER: 10.34.255.7#53(10.34.255.7)
;; WHEN: Wed Aug 18 18:04:06 2010
;; MSG SIZE  rcvd: 77
15.2.5.2. Looking Up an IP Address
To look up an IP address assigned to a particular domain, use the command in the following form: 
dig name A
In Example 15.18, “A sample IP address lookup”, the dig utility is used to display the IP address of example.com.

Example 15.18. A sample IP address lookup

~]$ dig example.com A

; <<>> DiG 9.7.1-P2-RedHat-9.7.1-2.P2.fc13 <<>> example.com A
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4849
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0

;; QUESTION SECTION:
;example.com.                   IN      A

;; ANSWER SECTION:
example.com.            155606  IN      A       192.0.32.10

;; AUTHORITY SECTION:
example.com.            99175   IN      NS      a.iana-servers.net.
example.com.            99175   IN      NS      b.iana-servers.net.

;; Query time: 1 msec
;; SERVER: 10.34.255.7#53(10.34.255.7)
;; WHEN: Wed Aug 18 18:07:25 2010
;; MSG SIZE  rcvd: 93
15.2.5.3. Looking Up a Host Name
To look up a host name for a particular IP address, use the command in the following form: 
dig -x address
In Example 15.19, “A Sample Host Name Lookup”, the dig utility is used to display the host name assigned to 192.0.32.10.

Example 15.19. A Sample Host Name Lookup

~]$ dig -x 192.0.32.10

; <<>> DiG 9.7.1-P2-RedHat-9.7.1-2.P2.fc13 <<>> -x 192.0.32.10
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 29683
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 5, ADDITIONAL: 6

;; QUESTION SECTION:
;10.32.0.192.in-addr.arpa.      IN      PTR

;; ANSWER SECTION:
10.32.0.192.in-addr.arpa. 21600 IN      PTR     www.example.com.

;; AUTHORITY SECTION:
32.0.192.in-addr.arpa.  21600   IN      NS      b.iana-servers.org.
32.0.192.in-addr.arpa.  21600   IN      NS      c.iana-servers.net.
32.0.192.in-addr.arpa.  21600   IN      NS      d.iana-servers.net.
32.0.192.in-addr.arpa.  21600   IN      NS      ns.icann.org.
32.0.192.in-addr.arpa.  21600   IN      NS      a.iana-servers.net.

;; ADDITIONAL SECTION:
a.iana-servers.net.     13688   IN      A       192.0.34.43
b.iana-servers.org.     5844    IN      A       193.0.0.236
b.iana-servers.org.     5844    IN      AAAA    2001:610:240:2::c100:ec
c.iana-servers.net.     12173   IN      A       139.91.1.10
c.iana-servers.net.     12173   IN      AAAA    2001:648:2c30::1:10
ns.icann.org.           12884   IN      A       192.0.34.126

;; Query time: 156 msec
;; SERVER: 10.34.255.7#53(10.34.255.7)
;; WHEN: Wed Aug 18 18:25:15 2010
;; MSG SIZE  rcvd: 310

15.2.6. Advanced Features of BIND

Most BIND implementations only use the named service to provide name resolution services or to act as an authority for a particular domain. However, BIND version 9 has a number of advanced features that allow for a more secure and efficient DNS service.

Important

Before attempting to use advanced features like DNSSEC, TSIG, or IXFR (Incremental Zone Transfer), make sure that the particular feature is supported by all nameservers in the network environment, especially when you use older versions of BIND or non-BIND servers.
All of the features mentioned are discussed in greater detail in the BIND 9 Administrator Reference Manual referenced in Section 15.2.8.1, “Installed Documentation”.
15.2.6.1. Multiple Views
Optionally, different information can be presented to a client depending on the network a request originates from. This is primarily used to deny sensitive DNS entries from clients outside of the local network, while allowing queries from clients inside the local network.
To configure multiple views, add the view statement to the /etc/named.conf configuration file. Use the match-clients option to match IP addresses or entire networks and give them special options and zone data.
15.2.6.2. Incremental Zone Transfers (IXFR)
Incremental Zone Transfers (IXFR) allow a secondary nameserver to only download the updated portions of a zone modified on a primary nameserver. Compared to the standard transfer process, this makes the notification and update process much more efficient.
Note that IXFR is only available when using dynamic updating to make changes to primary zone records. If manually editing zone files to make changes, Automatic Zone Transfer (AXFR) is used.
15.2.6.3. Transaction SIGnatures (TSIG)
Transaction SIGnatures (TSIG) ensure that a shared secret key exists on both primary and secondary nameservers before allowing a transfer. This strengthens the standard IP address-based method of transfer authorization, since attackers would not only need to have access to the IP address to transfer the zone, but they would also need to know the secret key.
Since version 9, BIND also supports TKEY, which is another shared secret key method of authorizing zone transfers.

Important

When communicating over an insecure network, do not rely on IP address-based authentication only.
15.2.6.4. DNS Security Extensions (DNSSEC)
Domain Name System Security Extensions (DNSSEC) provide origin authentication of DNS data, authenticated denial of existence, and data integrity. When a particular domain is marked as secure, the SERVFAIL response is returned for each resource record that fails the validation.
Note that to debug a DNSSEC-signed domain or a DNSSEC-aware resolver, you can use the dig utility as described in Section 15.2.5, “Using the dig Utility”. Useful options are +dnssec (requests DNSSEC-related resource records by setting the DNSSEC OK bit), +cd (tells recursive nameserver not to validate the response), and +bufsize=512 (changes the packet size to 512B to get through some firewalls).
15.2.6.5. Internet Protocol version 6 (IPv6)
Internet Protocol version 6 (IPv6) is supported through the use of AAAA resource records, and the listen-on-v6 directive as described in Table 15.3, “Commonly Used Configuration Options”.

15.2.7. Common Mistakes to Avoid

The following is a list of recommendations on how to avoid common mistakes users make when configuring a nameserver:
Use semicolons and curly brackets correctly
An omitted semicolon or unmatched curly bracket in the /etc/named.conf file can prevent the named service from starting.
Use period (the . character) correctly
In zone files, a period at the end of a domain name denotes a fully qualified domain name. If omitted, the named service will append the name of the zone or the value of $ORIGIN to complete it.
Increment the serial number when editing a zone file
If the serial number is not incremented, the primary nameserver will have the correct, new information, but the secondary nameservers will never be notified of the change, and will not attempt to refresh their data of that zone.
Configure the firewall
If a firewall is blocking connections from the named service to other nameservers, the recommended practice is to change the firewall settings.

Warning

Using a fixed UDP source port for DNS queries is a potential security vulnerability that could allow an attacker to conduct cache-poisoning attacks more easily. To prevent this, by default DNS sends from a random ephemeral port. Configure your firewall to allow outgoing queries from a random UDP source port. The range 1024 to 65535 is used by default.

15.2.8. Additional Resources

The following sources of information provide additional resources regarding BIND.
15.2.8.1. Installed Documentation
BIND features a full range of installed documentation covering many different topics, each placed in its own subject directory. For each item below, replace version with the version of the bind package installed on the system:
/usr/share/doc/bind-version/
The main directory containing the most recent documentation. The directory contains the BIND 9 Administrator Reference Manual in HTML and PDF formats, which details BIND resource requirements, how to configure different types of nameservers, how to perform load balancing, and other advanced topics.
/usr/share/doc/bind-version/sample/etc/
The directory containing examples of named configuration files.
rndc(8)
The manual page for the rndc name server control utility, containing documentation on its usage.
named(8)
The manual page for the Internet domain name server named, containing documentation on assorted arguments that can be used to control the BIND nameserver daemon.
lwresd(8)
The manual page for the lightweight resolver daemon lwresd, containing documentation on the daemon and its usage.
named.conf(5)
The manual page with a comprehensive list of options available within the named configuration file.
rndc.conf(5)
The manual page with a comprehensive list of options available within the rndc configuration file.
15.2.8.2. Online Resources
https://access.redhat.com/site/articles/770133
A Red Hat Knowledgebase article about running BIND in a chroot environment, including the differences compared to Red Hat Enterprise Linux 6.
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Security_Guide/
The Red Hat Enterprise Linux 7 Security Guide has a comprehensive section on DNSSEC.
https://www.icann.org/namecollision
The ICANN FAQ on domain name collision.

Chapter 16. Configuring the Squid Caching Proxy Server

Squid is a proxy server that caches content to reduce bandwidth and load web pages more quickly. This chapter describes how to set up Squid as a proxy for the HTTP, HTTPS, and FTP protocol, as well as authentication and restricting access.

16.1. Setting up Squid as a Caching Proxy Without Authentication

This section describes a basic configuration of Squid as a caching proxy without authentication. The procedure limits access to the proxy based on IP ranges.
Prerequisites
  • The procedure assumes that the /etc/squid/squid.conf file is as provided by the squid package. If you edited this file before, remove the file and reinstall the package.
Procedure
  1. Install the squid package: 
    # yum install squid
  2. Edit the /etc/squid/squid.conf file:
    1. Adapt the localnet access control lists (ACL) to match the IP ranges that should be allowed to use the proxy: 
      acl localnet src 192.0.2.0/24
acl localnet 2001:db8::/32
      By default, the /etc/squid/squid.conf file contains the http_access allow localnet rule that allows using the proxy from all IP ranges specified in localnet ACLs. Note that you must specify all localnet ACLs before the http_access allow localnet rule.

      Important

      Remove all existing acl localnet entries that do not match your environment.
    2. The following ACL exists in the default configuration and defines 443 as a port that uses the HTTPS protocol: 
      acl SSL_ports port 443
      If users should be able to use the HTTPS protocol also on other ports, add an ACL for each of these port: 
      acl SSL_ports port port_number
    3. Update the list of acl Safe_ports rules to configure to which ports Squid can establish a connection. For example, to configure that clients using the proxy can only access resources on port 21 (FTP), 80 (HTTP), and 443 (HTTPS), keep only the following acl Safe_ports statements in the configuration: 
      acl Safe_ports port 21
acl Safe_ports port 80
acl Safe_ports port 443
      By default, the configuration contains the http_access deny !Safe_ports rule that defines access denial to ports that are not defined in Safe_ports ACLs.
    4. Configure the cache type, the path to the cache directory, the cache size, and further cache type-specific settings in the cache_dir parameter: 
      cache_dir ufs /var/spool/squid 10000 16 256
      With these settings:
      • Squid uses the ufs cache type.
      • Squid stores its cache in the /var/spool/squid/ directory.
      • The cache grows up to 10000 MB.
      • Squid creates 16 level-1 sub-directories in the /var/spool/squid/ directory.
      • Squid creates 256 sub-directories in each level-1 directory.
      If you do not set a cache_dir directive, Squid stores the cache in memory.
  3. If you set a different cache directory than /var/spool/squid/ in the cache_dir parameter:
    1. Create the cache directory: 
      # mkdir -p path_to_cache_directory
    2. Configure the permissions for the cache directory: 
      # chown squid:squid path_to_cache_directory
    3. If you run SELinux in enforcing mode, set the squid_cache_t context for the cache directory: 
      # semanage fcontext -a -t squid_cache_t "path_to_cache_directory(/.*)?"
# restorecon -Rv path_to_cache_directory
      If the semanage utility is not available on your system, install the policycoreutils-python-utils package.
  4. Open the 3128 port in the firewall: 
    # firewall-cmd --permanent --add-port=3128/tcp
# firewall-cmd --reload
  5. Start the squid service: 
    # systemctl start squid
  6. Enable the squid service to start automatically when the system boots: 
    # systemctl enable squid
Verification Steps
To verify that the proxy works correctly, download a web page using the curl utility: 
# curl -O -L "https://www.redhat.com/index.html" -x "proxy.example.com:3128"
If curl does not display any error and the index.html file was downloaded to the current directory, the proxy works.

16.2. Setting up Squid as a Caching Proxy With LDAP Authentication

This section describes a basic configuration of Squid as a caching proxy that uses LDAP to authenticate users. The procedure configures that only authenticated users can use the proxy.
Prerequisites
  • The procedure assumes that the /etc/squid/squid.conf file is as provided by the squid package. If you edited this file before, remove the file and reinstall the package.
  • An service user, such as uid=proxy_user,cn=users,cn=accounts,dc=example,dc=com exists in the LDAP directory. Squid uses this account only to search for the authenticating user. If the authenticating user exists, Squid binds as this user to the directory to verify the authentication.
Procedure
  1. Install the squid package: 
    # yum install squid
  2. Edit the /etc/squid/squid.conf file:
    1. To configure the basic_ldap_auth helper utility, add the following configuration entry to the top of /etc/squid/squid.conf: 
      auth_param basic program /usr/lib64/squid/basic_ldap_auth -b "cn=users,cn=accounts,dc=example,dc=com" -D "uid=proxy_user,cn=users,cn=accounts,dc=example,dc=com" -W /etc/squid/ldap_password -f "(&(objectClass=person)(uid=%s))" -ZZ -H ldap://ldap_server.example.com:389
      The following describes the parameters passed to the basic_ldap_auth helper utility in the example above:
      • -B base_DN sets the LDAP search base.
      • -D proxy_service_user_DN sets the distinguished name (DN) of the account Squid uses to search for the authenticating user in the directory.
      • -W path_to_password_file sets the path to the file that contains the password of the proxy service user. Using a password file prevents that the password is visible in the operating system's process list.
      • -f LDAP_filter specifies the LDAP search filter. Squid replaces the %s variable with the user name provided by the authenticating user.
        The (&(objectClass=person)(uid=%s)) filter in the example defines that the user name must match the value set in the uid attribute and that the directory entry contains the person object class.
      • -ZZ enforces a TLS-encrypted connection over the LDAP protocol using the STARTTLS command. Omit the -ZZ in the following situations:
        • The LDAP server does not support encrypted connections.
        • The port specified in the URL uses the LDAPS protocol.
      • The -H LDAP_URL parameter specifies the protocol, the host name or IP address, and the port of the LDAP server in URL format.
    2. Add the following ACL and rule to configure that Squid allows only authenticated users to use the proxy: 
      acl ldap-auth proxy_auth REQUIRED
http_access allow ldap-auth

      Important

      Specify these settings before the http_access deny all rule.
    3. Remove the following rule to disable bypassing the proxy authentication from IP ranges specified in localnet ACLs: 
      http_access allow localnet
    4. The following ACL exists in the default configuration and defines 443 as a port that uses the HTTPS protocol: 
      acl SSL_ports port 443
      If users should be able to use the HTTPS protocol also on other ports, add an ACL for each of these port: 
      acl SSL_ports port port_number
    5. Update the list of acl Safe_ports rules to configure to which ports Squid can establish a connection. For example, to configure that clients using the proxy can only access resources on port 21 (FTP), 80 (HTTP), and 443 (HTTPS), keep only the following acl Safe_ports statements in the configuration: 
      acl Safe_ports port 21
acl Safe_ports port 80
acl Safe_ports port 443
      By default, the configuration contains the http_access deny !Safe_ports rule that defines access denial to ports that are not defined in Safe_ports ACLs.
    6. Configure the cache type, the path to the cache directory, the cache size, and further cache type-specific settings in the cache_dir parameter: 
      cache_dir ufs /var/spool/squid 10000 16 256
      With these settings:
      • Squid uses the ufs cache type.
      • Squid stores its cache in the /var/spool/squid/ directory.
      • The cache grows up to 10000 MB.
      • Squid creates 16 level-1 sub-directories in the /var/spool/squid/ directory.
      • Squid creates 256 sub-directories in each level-1 directory.
      If you do not set a cache_dir directive, Squid stores the cache in memory.
  3. If you set a different cache directory than /var/spool/squid/ in the cache_dir parameter:
    1. Create the cache directory: 
      # mkdir -p path_to_cache_directory
    2. Configure the permissions for the cache directory: 
      # chown squid:squid path_to_cache_directory
    3. If you run SELinux in enforcing mode, set the squid_cache_t context for the cache directory: 
      # semanage fcontext -a -t squid_cache_t "path_to_cache_directory(/.*)?"
# restorecon -Rv path_to_cache_directory
      If the semanage utility is not available on your system, install the policycoreutils-python-utils package.
  4. Store the password of the LDAP service user in the /etc/squid/ldap_password file, and set appropriate permissions for the file: 
    # echo "password" > /etc/squid/ldap_password
# chown root:squid /etc/squid/ldap_password
# chmod 640 /etc/squid/ldap_password
  5. Open the 3128 port in the firewall: 
    # firewall-cmd --permanent --add-port=3128/tcp
# firewall-cmd --reload
  6. Start the squid service: 
    # systemctl start squid
  7. Enable the squid service to start automatically when the system boots: 
    # systemctl enable squid
Verification Steps
To verify that the proxy works correctly, download a web page using the curl utility: 
# curl -O -L "https://www.redhat.com/index.html" -x "user_name:password@proxy.example.com:3128"
If curl does not display any error and the index.html file was downloaded to the current directory, the proxy works.
Troubleshooting Steps
To verify that the helper utility works correctly:
  1. Manually start the helper utility with the same settings you used in the auth_param parameter: 
    # /usr/lib64/squid/basic_ldap_auth -b "cn=users,cn=accounts,dc=example,dc=com" -D "uid=proxy_user,cn=users,cn=accounts,dc=example,dc=com" -W /etc/squid/ldap_password -f "(&(objectClass=person)(uid=%s))" -ZZ -H ldap://ldap_server.example.com:389
  2. Enter a valid user name and password, and press Enter: 
    user_name password
    If the helper utility returns OK, authentication succeeded.

16.3. Setting up Squid as a Caching Proxy With Kerberos Authentication

This section describes a basic configuration of Squid as a caching proxy that authenticates users to an Active Directory (AD) using Kerberos. The procedure configures that only authenticated users can use the proxy.
Prerequisites
  • The procedure assumes that the /etc/squid/squid.conf file is as provided by the squid package. If you edited this file before, remove the file and reinstall the package.
  • The server on which you want to install Squid is a member of the AD domain. For details, see Setting up Samba as a Domain Member in the Red Hat Enterprise Linux 7 System Administrator's Guide.
Procedure
  1. Install the following packages: 
    # yum install squid krb5-workstation
  2. Authenticate as the AD domain administrator: 
    # kinit administrator@AD.EXAMPLE.COM
  3. Create a keytab for Squid and store it in the /etc/squid/HTTP.keytab file: 
    # export KRB5_KTNAME=FILE:/etc/squid/HTTP.keytab
# net ads keytab CREATE -U administrator
  4. Add the HTTP service principal to the keytab: 
    # net ads keytab ADD HTTP -U administrator
  5. Set the owner of the keytab file to the squid user: 
    # chown squid /etc/squid/HTTP.keytab
  6. Optionally, verify that the keytab file contains the HTTP service principal for the fully-qualified domain name (FQDN) of the proxy server: 
    #  klist -k /etc/squid/HTTP.keytab
Keytab name: FILE:/etc/squid/HTTP.keytab
KVNO Principal
---- --------------------------------------------------------------------------
...
   2 HTTP/proxy.ad.example.com@AD.EXAMPLE.COM
...
  7. Edit the /etc/squid/squid.conf file:
    1. To configure the negotiate_kerberos_auth helper utility, add the following configuration entry to the top of /etc/squid/squid.conf: 
      auth_param negotiate program /usr/lib64/squid/negotiate_kerberos_auth -k /etc/squid/HTTP.keytab -s HTTP/proxy.ad.example.com@AD.EXAMPLE.COM
      The following describes the parameters passed to the negotiate_kerberos_auth helper utility in the example above:
      • -k file sets the path to the key tab file. Note that the squid user must have read permissions on this file.
      • -s HTTP/host_name@kerberos_realm sets the Kerberos principal that Squid uses.
      Optionally, you can enable logging by passing one or both of the following parameters to the helper utility:
      • -i logs informational messages, such as the authenticating user.
      • -d enables debug logging.
      Squid logs the debugging information from the helper utility to the /var/log/squid/cache.log file.
    2. Add the following ACL and rule to configure that Squid allows only authenticated users to use the proxy: 
      acl kerb-auth proxy_auth REQUIRED
http_access allow kerb-auth

      Important

      Specify these settings before the http_access deny all rule.
    3. Remove the following rule to disable bypassing the proxy authentication from IP ranges specified in localnet ACLs: 
      http_access allow localnet
    4. The following ACL exists in the default configuration and defines 443 as a port that uses the HTTPS protocol: 
      acl SSL_ports port 443
      If users should be able to use the HTTPS protocol also on other ports, add an ACL for each of these port: 
      acl SSL_ports port port_number
    5. Update the list of acl Safe_ports rules to configure to which ports Squid can establish a connection. For example, to configure that clients using the proxy can only access resources on port 21 (FTP), 80 (HTTP), and 443 (HTTPS), keep only the following acl Safe_ports statements in the configuration: 
      acl Safe_ports port 21
acl Safe_ports port 80
acl Safe_ports port 443
      By default, the configuration contains the http_access deny !Safe_ports rule that defines access denial to ports that are not defined in Safe_ports ACLs.
    6. Configure the cache type, the path to the cache directory, the cache size, and further cache type-specific settings in the cache_dir parameter: 
      cache_dir ufs /var/spool/squid 10000 16 256
      With these settings:
      • Squid uses the ufs cache type.
      • Squid stores its cache in the /var/spool/squid/ directory.
      • The cache grows up to 10000 MB.
      • Squid creates 16 level-1 sub-directories in the /var/spool/squid/ directory.
      • Squid creates 256 sub-directories in each level-1 directory.
      If you do not set a cache_dir directive, Squid stores the cache in memory.
  8. If you set a different cache directory than /var/spool/squid/ in the cache_dir parameter:
    1. Create the cache directory: 
      # mkdir -p path_to_cache_directory
    2. Configure the permissions for the cache directory: 
      # chown squid:squid path_to_cache_directory
    3. If you run SELinux in enforcing mode, set the squid_cache_t context for the cache directory: 
      # semanage fcontext -a -t squid_cache_t "path_to_cache_directory(/.*)?"
# restorecon -Rv path_to_cache_directory
      If the semanage utility is not available on your system, install the policycoreutils-python-utils package.
  9. Open the 3128 port in the firewall: 
    # firewall-cmd --permanent --add-port=3128/tcp
# firewall-cmd --reload
  10. Start the squid service: 
    # systemctl start squid
  11. Enable the squid service to start automatically when the system boots: 
    # systemctl enable squid
Verification Steps
To verify that the proxy works correctly, download a web page using the curl utility: 
# curl -O -L "https://www.redhat.com/index.html" --proxy-negotiate -u : -x "proxy.ad.example.com:3128"
If curl does not display any error and the index.html file exists in the current directory, the proxy works.
Troubleshooting Steps
To manually test Kerberos authentication:
  1. Obtain a Kerberos ticket for the AD account: 
    # kinit user@AD.EXAMPLE.COM
  2. Optionally, display the ticket: 
    # klist
  3. Use the negotiate_kerberos_auth_test utility to test the authentication: 
    # /usr/lib64/squid/negotiate_kerberos_auth_test proxy.ad.example.com
    If the helper utility returns a token, the authentication succeeded. 
    Token: YIIFtAYGKwYBBQUCoIIFqDC...

16.4. Configuring a Domain Blacklist in Squid

Frequently, administrators want to block access to specific domains. This section describes how to configure a domain blacklist in Squid.
Prerequisites
  • Squid is configured, and users can use the proxy.
Procedure
  1. Edit the /etc/squid/squid.conf file and add the following settings: 
    acl domain_blacklist dstdomain "/etc/squid/domain_blacklist.txt"
http_access deny all domain_blacklist

    Important

    Add these entries before the first http_access allow statement that allows access to users or clients.
  2. Create the /etc/squid/domain_blacklist.txt file and add the domains you want to block. For example, to block access to example.com including subdomains and to block example.net, add: 
    .example.com
example.net

    Important

    If you referred to the /etc/squid/domain_blacklist.txt file in the squid configuration, this file must not be empty. If the file is empty, Squid fails to start.
  3. Restart the squid service: 
    # systemctl restart squid

16.5. Configuring the Squid Service to Listen on a Specific Port or IP Address

By default, the Squid proxy service listens on the 3128 port on all network interfaces. This section describes how to change the port and configuring Squid to listen on a specific IP address.
Prerequisites
  • Squid is installed.
Procedure
  1. Edit the /etc/squid/squid.conf file:
    • To set the port on which the Squid service listens, set the port number in the http_port parameter. For example, to set the port to 8080, set: 
      http_port 8080
    • To configure on which IP address the Squid service listens, set the IP address and port number in the http_port parameter. For example, to configure that Squid listens only on the 192.0.2.1 IP address on port 3128, set: 
      http_port 192.0.2.1:3128
    Add multiple http_port parameters to the configuration file to configure that Squid listens on multiple ports and IP addresses: 
    http_port 192.0.2.1:3128
http_port 192.0.2.1:8080
  2. If you configured that Squid uses a different port as the default (3128):
    1. Open the port in the firewall: 
      # firewall-cmd --permanent --add-port=port_number/tcp
# firewall-cmd --reload
    2. If you run SELinux in enforcing mode, assign the port to the squid_port_t port type definition: 
      # semanage port -a -t squid_port_t -p tcp port_number
      If the semanage utility is not available on your system, install the policycoreutils-python-utils package.
  3. Restart the squid service: 
    # systemctl restart squid

16.6. Additional Resources

  • See the /usr/share/doc/squid-<version>/squid.conf.documented file for a list of all configuration parameters you can set in the /etc/squid/squid.conf file together with a detailed description.

Appendix A. Red Hat Customer Portal Labs Relevant to Networking

Red Hat Customer Portal Labs are tools designed to help you improve performance, troubleshoot issues, identify security problems, and optimize configuration. This appendix provides an overview of Red Hat Customer Portal Labs relevant to networking. All Red Hat Customer Portal Labs are available at https://access.redhat.com/labs/.

Bridge Configuration

The Bridge Configuration is designed to configure a bridged network interface for applications such as KVM using Red Hat Enterprise Linux 5.4 or later.

Network Bonding Helper

The Network Bonding Helper allows administrators to bind multiple Network Interface Controllers together into a single channel using the bonding kernel module and the bonding network interface.
Use the Network Bonding Helper to enable two or more network interfaces to act as one bonding interface.

Packet capture syntax generator

The Packet capture syntax generator helps you to capture network packets.
Use the Packet capture syntax generator to generate the tcpdump command that selects an interface and then prints information to the console. You need root access to enter the command.

Appendix B. Revision History

Revision History
Revision 0.10-06Tue 03 Mar 2020Marc Muehlfeld
Added the Configuring Policy-based Routing to Define Alternative Routes section.
Revision 0.10-05Fri 22 Nov 2019Marc Muehlfeld
Rewrote the Configuring the Squid Caching Proxy Server chapter.
Revision 0.10-04Tue 06 Aug 2019Marc Muehlfeld
Version for 7.7 GA publication.
Revision 0.10-03Thu 22 Mar 2018Ioanna Gkioka
Version for 7.5 GA publication.
Revision 0.10-02Mon 14 Aug 2017Ioanna Gkioka
Async release with misc. updates
Revision 0.10-01Tue 25 Jul 2017Mirek Jahoda
Version for 7.4 GA publication.
Revision 0.9-30Tue 18 Oct 2016Mirek Jahoda
Version for 7.3 GA publication.
Revision 0.9-25Wed 11 Nov 2015Jana Heves
Version for 7.2 GA release.
Revision 0.9-15Tue 17 Feb 2015Christian Huffman
Version for 7.1 GA release
Revision 0.9-14Fri Dec 05 2014Christian Huffman
Updated the nmtui and NetworkManager GUI sections.
Revision 0.9-12Wed Nov 05 2014Stephen Wadeley
Improved IP Networking, 802.1Q VLAN tagging, and Teaming.
Revision 0.9-11Tues Oct 21 2014Stephen Wadeley
Improved Bonding, Bridging, and Teaming.
Revision 0.9-9Tue Sep 2 2014Stephen Wadeley
Improved Bonding and Consistent Network Device Naming.
Revision 0.9-8Tue July 8 2014Stephen Wadeley
Red Hat Enterprise Linux 7.0 GA release of the Networking Guide.
Revision 0-0Wed Dec 12 2012Stephen Wadeley
Initialization of the Red Hat Enterprise Linux 7 Networking Guide.

B.1. Acknowledgments

Certain portions of this text first appeared in the Red Hat Enterprise Linux 6 Deployment Guide, copyright © 2014 Red Hat, Inc., available at https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/index.html.

Index

Symbols

/etc/named.conf (see BIND)

A

authoritative name server (see BIND)

B

Berkeley Internet Name Domain (see BIND)
BIND
additional resources, Online Resources
installed documentation, Installed Documentation
common mistakes, Common Mistakes to Avoid
configuration
acl statement, Common Statement Types
comment tags, Comment Tags
controls statement, Other Statement Types
include statement, Common Statement Types
key statement, Other Statement Types
logging statement, Other Statement Types
options statement, Common Statement Types
server statement, Other Statement Types
trusted-keys statement, Other Statement Types
view statement, Other Statement Types
zone statement, Common Statement Types
directories
/etc/named/, Configuring the named Service
/var/named/, Editing Zone Files
/var/named/data/, Editing Zone Files
/var/named/dynamic/, Editing Zone Files
/var/named/slaves/, Editing Zone Files
features
Automatic Zone Transfer (AXFR), Incremental Zone Transfers (IXFR)
DNS Security Extensions (DNSSEC), DNS Security Extensions (DNSSEC)
Incremental Zone Transfer (IXFR), Incremental Zone Transfers (IXFR)
Internet Protocol version 6 (IPv6), Internet Protocol version 6 (IPv6)
multiple views, Multiple Views
Transaction SIGnature (TSIG), Transaction SIGnatures (TSIG)
files
/etc/named.conf, Configuring the named Service, Configuring the Utility
/etc/rndc.conf, Configuring the Utility
/etc/rndc.key, Configuring the Utility
resource record, Name server Zones
types
authoritative name server, Name server Types
primary (master) name server, Name server Zones, Name server Types
recursive name server, Name server Types
secondary (slave) name server, Name server Zones, Name server Types
utilities
dig, BIND as a Name server, Using the dig Utility, DNS Security Extensions (DNSSEC)
named, BIND as a Name server, Configuring the named Service
rndc, BIND as a Name server, Using the rndc Utility
zones
$INCLUDE directive, Common Directives
$ORIGIN directive, Common Directives
$TTL directive, Common Directives
A (Address) resource record, Common Resource Records
CNAME (Canonical Name) resource record, Common Resource Records
comment tags, Comment Tags
description, Name server Zones
example usage, A Simple Zone File, A Reverse Name Resolution Zone File
MX (Mail Exchange) resource record, Common Resource Records
NS (Nameserver) resource record, Common Resource Records
PTR (Pointer) resource record, Common Resource Records
SOA (Start of Authority) resource record, Common Resource Records
bonding (see channel bonding)

C

channel bonding
configuration, Using Channel Bonding
description, Using Channel Bonding
parameters to bonded interfaces, Bonding Module Directives
channel bonding interface (see kernel module)

D

DHCP, DHCP Servers
additional resources, Additional Resources
command-line options, Starting and Stopping the Server
dhcpd.conf, Configuration File
dhcpd.leases, Starting and Stopping the Server
dhcpd6.conf, DHCP for IPv6 (DHCPv6)
DHCPv6, DHCP for IPv6 (DHCPv6)
dhcrelay, DHCP Relay Agent
global parameters, Configuration File
group, Configuration File
options, Configuration File
reasons for using, Why Use DHCP?
Relay Agent, DHCP Relay Agent
server configuration, Configuring a DHCP Server
shared-network, Configuration File
starting the server, Starting and Stopping the Server
stopping the server, Starting and Stopping the Server
subnet, Configuration File
dhcpd.conf, Configuration File
dhcpd.leases, Starting and Stopping the Server
dhcrelay, DHCP Relay Agent
dig (see BIND)
DNS
definition, DNS Servers
(see also BIND)
Dynamic Host Configuration Protocol (see DHCP)

K

kernel module
bonding module, Using Channel Bonding
description, Using Channel Bonding
parameters to bonded interfaces, Bonding Module Directives
module parameters
bonding module parameters, Bonding Module Directives

M

Multihomed DHCP
host configuration, Host Configuration
server configuration, Configuring a Multihomed DHCP Server

N

name server (see DNS)
named (see BIND)
NIC
binding into single channel, Using Channel Bonding

P

primary name server (see BIND)

R

recursive name server (see BIND)
resource record (see BIND)
rndc (see BIND)
root name server (see BIND)

S

secondary name server (see BIND)

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