1. Invoke the linuxconf tool. ( type linuxconf in the shell prompt and press Enter ). For starting this tool you have to be logged in as Super user.

2. In the displayed menu, select the menu item : IP Aliases for virtual hosts and press Enter. This will display the two interfaces eth0 and lo. (Ethernet interfaces in Linux are called by such names as eth0 and eth1)

3. Select eth0 and press Enter. This will show all the IP aliases configured for the selected interface.

4. Example

   IP alias or range : 177.177.177.1-25
   Netmask : 255.255.255.0

5. In the field IP alias or range, enter the desired IP address or the range with a corresponding Netmask.

 

Note: These commands have to be executed with the super user privilege. You will have to re-start the system for the changes to take effect. When you are configuring a large number of IP address, it might take a long time to boot up.

Using the following command, we can configure Virtual IPs in the Linux box at run-time without re-booting the machine or re-starting the network.

 ifconfig eth0:1 172.19.1.2 netmask 255.255.255.0   up

ifconfig eth0:3 172.19.1.3 netmask 255.255.255.0   up

 The interface number must be unique for each interface (for example eth0:1, eth0:2 etc). The same interfaces can be made down by using the following command.

 ifconfig eth0:1 172.19.1.2 netmask 255.255.255.0   down

ifconfig eth0:3 172.19.1.3 netmask 255.255.255.0   down

 

Note: These commands have to be executed with the super user privilege. It can be used in versions up to 7.2 The configurations will not be available when you re-start your system. Thanks to http://techgurulive.com/2009/03/07/how-to-configure-virtual-ip-address-in-linux/