Setting up multiple IP addresses on a single NIC in Linux

In linux, you can bind multiple IP addresses on a single NIC. This is usually done in case you are using your linux machine as a web server and is hosting multiple domains and you want to bind each domain to a unique IP address. This is how it is done.

Let us assume that you already have a NIC which is bound with a static IP address. Then you will have a file called /etc/sysconfig/network-scripts/ifcfg-eth0 .Myifcfg-eth0 file has the following entries:

# File: ifcfg-eth0
DEVICE=eth0
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.0.1
NETMASK=255.255.255.0
BROADCAST=192.168.0.255
NETWORK=192.168.0.0
HWADDR=00:80:48:34:C2:84

Now to bind another IP address to the same NIC, I create a copy of the above file ifcfg-eth0 and name it as ifcfg-eth0:1

# cd /etc/sysconfig/networking-scripts
# cp ifcfg-eth0  ifcfg-eth0:1

Now just change the values of the DEVICE and IPADDR in the file as follows:

# File: ifcfg-eth0:1
DEVICE=eth0:1
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.0.5
NETMASK=255.255.255.0
BROADCAST=192.168.0.255
NETWORK=192.168.0.0
HWADDR=00:80:48:34:C2:84

And lastly, restart the networking service. If you are using RedHat, then it is as simple as :

# service network restart

Note: If you do not know how to configure a NIC, see my previous posts - How to install a network card in Linux and How to assign an IP address.