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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.
Note
In Red Hat Enterprise Linux 6, NetworkManager now reads
ifcfg
alias files and assigns the addresses in them to their master interface, using the alias name as the address label. For example, if ifcfg-eth0
and ifcfg-eth0:1
files are present, NetworkManager reads the alias file's DEVICE line and stores this as an address label. The use of secondary addresses rather than alias is still preferred.
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.
Warning
Alias interfaces do not support
DHCP
.
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.