Adding an alias to an ethernet interface using ifconfig

To add an address to an ethernet interface :

ifconfig ethx:n [ipaddress]

where :
x = ethernet number
n = alias number

example

ifconfig eth0:1 10.0.0.10
will add 10.0.0.10 to eth0 in addition to the existing ip address [eth0]

Link : Setting up IP Aliasing on A Linux Machine Mini-HOWTO