Sometimes you need to bind a second IP address to a Network Interface Card.  Maybe you need access to another network temporarily or you just need to fix something that comes with a default address not on your network.

From Linux, you can execute the following command:

ifconfig eth0:1 192.168.5.16 netmask 255.255.255.0 up

This will add a second IP Address to your eth0 network interface.

For computers to talk on a network, they need a unique address.  The most common type of address is an Internet Protocol, or IP, address.  The address consists of a network portion and a device (computer) portion.  I use the term "device" only because it could be something other than a computer, like a printer.  It isn’t critical to understanding IP Addresses that there is a separate network portion and a separate device portion, but it does become important when you to want to understand how data moves across your personal network and across the internet.