Creating network aliases for single network interface

First some assumptions:

• network interface is aliased to eth0
• eth0 assigned to 192.168.1.1
  

Here's how you assign more than one IP to a single network interface in Ubuntu/Debian:

# ifconfig eth0:0 192.168.1.2 up

That's it.  Wait for a while for the interface to become active and you'll be able to configure services to serve from that IP.  To make the change permanent, edit the /etc/network/interfaces file and add the following lines:

auto eth0:0
iface eth0:0 inet static
        address 192.168.1.2
        netmask 255.255.255.0
        gateway 192.168.1.0