11.2.8. Alias and Clone Files

Two lesser-used types of interface configuration files are alias and clone files. As the ip utility now supports assigning multiple addresses to the same interface it is no longer necessary to use this 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 eth1
~]# ip address add 192.168.4.223/24 dev eth1
~]# ip addr
3: eth1: <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 eth1
    inet 192.168.4.223/24 scope global eth1

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 6 is iproute.

For new installations, users should select the Manual method on the IPv4 or IPv6 tab in NetworkManager to assign multiple IP address to the same interface. For more information on using this tool, see Chapter 10, NetworkManager.

Alias interface configuration files, which are used to bind multiple addresses to a single interface, use the ifcfg-if-name:alias-value naming scheme.

For example, an ifcfg-eth0:0 file could be configured to specify DEVICE=eth0:0 and a static IP address of 10.0.0.2, serving as an alias of an Ethernet interface already configured to receive its IP information via DHCP in ifcfg-eth0. Under this configuration, eth0 is bound to a dynamic IP address, but the same physical network card can receive requests via the fixed, 10.0.0.2 IP address.

A clone interface configuration file should use the following naming convention: ifcfg-if-name-clone-name. While an alias file allows multiple addresses for an existing interface, a clone file is used to specify additional options for an interface. For example, a standard DHCP Ethernet interface called eth0, may look similar to this:

DEVICE=eth0
ONBOOT=yes
BOOTPROTO=dhcp

Since the default value for the USERCTL directive is no if it is not specified, users cannot bring this interface up and down. To give users the ability to control the interface, create a clone by copying ifcfg-eth0 to ifcfg-eth0-user and add the following line to ifcfg-eth0-user:

USERCTL=yes

This way a user can bring up the eth0 interface using the /sbin/ifup eth0-user command because the configuration options from ifcfg-eth0 and ifcfg-eth0-user are combined. While this is a very basic example, this method can be used with a variety of options and interfaces.

It is no longer possible to create alias and clone interface configuration files using a graphical tool. However, as explained at the beginning of this section, it is no longer necessary to use this method as it is now possible to directly assign multiple IP address to the same interface. For new installations, users should select the Manual method on the IPv4 or IPv6 tab in NetworkManager to assign multiple IP address to the same interface. For more information on using this tool, see Chapter 10, NetworkManager.