Linux – Persist IP address alias across reboots in CentOS/RHEL 6 using “ip” command

You can use the lsb_release command on various Linux distributions:

lsb_release -i -r 

This will tell you the Distribution and Version and is a little bit more accurate than accessing files that may or may not have been modified by the admin or a software package. As well as working across multiple distros.

For RHEL, you should use:

cat /etc/redhat-release

It is the same machine with multiple ips, Linux is capable of mapping multiple IP addresses to a single NIC by using IP aliasing.

To set up an IP alias, for example:

ifconfig eth0:0 192.198.5.2 netmask 255.255.255.0 up

This assigns the IP address 192.198.5.2 to eth0 as the first alias (noted as eth0:0) on eth0. If you look at the output of ifconfig, you'll see the distinct IP address for eth0 and another for eth0:0.

The aliases are NetworkInterface:Number for example eth0:0, eth0:1, eth0:2 and so forth.

In some systems you can simple create the aliases file ifcfg-ethX:Y (where X is the Network Interface and Y the alias) in the directory /etc/sysconfig/network-scripts/ and it will read on boot / network restart.

The content of the file is similar to the other interface files, for example:

DEVICE=eth0
ONBOOT=yes
IPADDR="192.198.5.2"
NETMASK="255.255.255.0"

On systems that don't use these network scripts, just add the call to ifconfig directly in your startup script (usually /etc/rc.d/rc.local).