16.2. Interface Configuration Files
Interface configuration 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 <name> refers to the name of the device that the configuration file controls.
16.2.1. Ethernet Interfaces
One of the most common interface files is
/etc/sysconfig/network-scripts/ifcfg-eth0, which controls the first Ethernet network interface card or NIC in the system. In a system with multiple NICs, there are multiple ifcfg-eth<X> files (where <X> is a unique number corresponding to a specific interface). Because each device has its own configuration file, an administrator can control how each interface functions individually.
The following is a sample
ifcfg-eth0 file for a system using a fixed IP address:
DEVICE=eth0 BOOTPROTO=none ONBOOT=yes NETMASK=255.255.255.0 IPADDR=10.0.1.27 USERCTL=no
The values required in an interface configuration file can change based on other values. For example, the
ifcfg-eth0 file for an interface using DHCP looks different because IP information is provided by the DHCP server:
DEVICE=eth0 BOOTPROTO=dhcp ONBOOT=yes
The Network Administration Tool (
system-config-network) is an easy way to make changes to the various network interface configuration files (refer to Chapter 17, Network Configuration for detailed instructions on using this tool).
However, it is also possible to manually edit the configuration files for a given network interface.
Below is a listing of the configurable parameters in an Ethernet interface configuration file:
-
BONDING_OPTS=<parameters> - sets the configuration parameters for the bonding device, and is used in
/etc/sysconfig/network-scripts/ifcfg-bond<N>(see Section 16.2.3, “Channel Bonding Interfaces”). These parameters are identical to those used for bonding devices in/sys/class/net/<bonding device>/bonding, and the module parameters for the bonding driver as described inbondingModule Directives.This configuration method is used so that multiple bonding devices can have different configurations. If you useBONDING_OPTSinifcfg-<name>, do not use/etc/modprobe.confto specify options for the bonding device. -
BOOTPROTO=<protocol> - where
<protocol>is one of the following:none— No boot-time protocol should be used.bootp— The BOOTP protocol should be used.dhcp— TheDHCPprotocol should be used.
-
BROADCAST=<address> - where
<address>is the broadcast address. This directive is deprecated, as the value is calculated automatically withipcalc. -
DEVICE=<name> - where
<name>is the name of the physical device (except for dynamically-allocated PPP devices where it is the logical name). -
DHCP_HOSTNAME=<name> - where
<name>is a short host name to be sent to theDHCPserver. Use this option only if theDHCPserver requires the client to specify a host name before receiving anIPaddress. -
DNS{1,2}=<address> - where
<address>is a name server address to be placed in/etc/resolv.confif thePEERDNSdirective is set toyes. -
ETHTOOL_OPTS=<options> - where
<options>are any device-specific options supported byethtool. For example, if you wanted to force 100Mb, full duplex:ETHTOOL_OPTS="autoneg off speed 100 duplex full"
Instead of a custom initscript, useETHTOOL_OPTSto set the interface speed and duplex settings. Custom initscripts run outside of the network init script lead to unpredictable results during a post-boot network service restart.Note
Changing speed or duplex settings almost always requires disabling autonegotiation with theautoneg offoption. This needs to be stated first, as the option entries are order-dependent. -
GATEWAY=<address> - where <address> is the
IPaddress of the network router or gateway device (if any). -
HOTPLUG=<answer> - where <answer> is one of the following:
yes— This device should be activated when it is hot-plugged (this is the default option).no— This device should not be activated when it is hot-plugged.
TheHOTPLUG=nooption can be used to prevent a channel bonding interface from being activated when a bonding kernel module is loaded.Refer to Section 16.2.3, “Channel Bonding Interfaces” for more about channel bonding interfaces. -
HWADDR=<MAC-address> - where <MAC-address> is the hardware address of the Ethernet device in the form AA:BB:CC:DD:EE:FF. This directive must be used in machines containing more than one NIC to ensure that the interfaces are assigned the correct device names regardless of the configured load order for each NIC's module. This directive should not be used in conjunction with
MACADDR. -
IPADDR=<address> - where
<address>is theIPaddress. -
LINKDELAY=<time> - where <time> is the number of seconds to wait for link negotiation before configuring the device.
-
MACADDR=<MAC-address> - where <MAC-address> is the hardware address of the Ethernet device in the form AA:BB:CC:DD:EE:FF. This directive is used to assign a MAC address to an interface, overriding the one assigned to the physical NIC. This directive should not be used in conjunction with
HWADDR. -
MASTER=<bond-interface> - where
<bond-interface>is the channel bonding interface to which the Ethernet interface is linked.This directive is used in conjunction with theSLAVEdirective.Refer to Section 16.2.3, “Channel Bonding Interfaces” for more information about channel bonding interfaces. -
NETMASK=<mask> - where
<mask>is the netmask value. -
NETWORK=<address> - where
<address>is the network address. This directive is deprecated, as the value is calculated automatically withipcalc. -
ONBOOT=<answer> - where
<answer>is one of the following:yes— This device should be activated at boot-time.no— This device should not be activated at boot-time.
-
PEERDNS=<answer> - where
<answer>is one of the following:yes— Modify/etc/resolv.confif the DNS directive is set. If usingDHCP, thenyesis the default.no— Do not modify/etc/resolv.conf.
-
SLAVE=<answer> - where
<answer>is one of the following:yes— This device is controlled by the channel bonding interface specified in theMASTERdirective.no— This device is not controlled by the channel bonding interface specified in theMASTERdirective.
This directive is used in conjunction with theMASTERdirective.Refer to Section 16.2.3, “Channel Bonding Interfaces” for more about channel bonding interfaces. -
SRCADDR=<address> - where
<address>is the specified sourceIPaddress for outgoing packets. -
USERCTL=<answer> - where
<answer>is one of the following:yes— Non-root users are allowed to control this device.no— Non-root users are not allowed to control this device.
