This tutorial describes how to permanently add any number of static IP addresses to a network interface from the console. Login as root and open /etc/network/interfaces in your favorite editor. By default, it should look something like this:

# The loopback network interface
auto lo
iface lo inet loopback

Let's assume your network interface is eth0. To assign it a static IP address, add the following lines to /etc/network/interfaces:

auto eth0
iface eth0 inet static
        address 192.168.0.41
        netmask 255.255.255.0
        broadcast 192.168.0.255
        gateway 192.168.0.1

You should of course replace the values for address, netmask, gateway, and broadcast with values specific to your desired IP address and network. Additional static IP's can be added by repeating the above code in the interfaces file. Just increment the interfaces using "eth0:1", "eth0:2", etc, for each IP address. Example:

# The loopback network interface
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
        address 192.168.0.41
        netmask 255.255.255.0
        broadcast 192.168.0.255
        gateway 192.168.0.1

auto eth0:1
iface eth0:1 inet static
        address 192.168.0.56
        netmask 255.255.255.0
        broadcast 192.168.0.255
        gateway 192.168.0.1
		
auto eth0:2
iface eth0:2 inet static
        address 192.168.0.89
        netmask 255.255.255.0
        broadcast 192.168.0.255
        gateway 192.168.0.1

If you're not using DHCP at all, you may need to add/edit your DNS servers. Open up /etc/resolv.conf and make sure the IP's of your DNS servers are in there. For example:

nameserver 192.168.0.1
nameserver 192.168.0.2

Finally, restart the network interfaces.

/etc/init.d/networking restart

If you're SSH'd into the box, don't log out yet. Log into the box with a new SSH session to verify the network interface came back up. Once verified, try pinging the new IP from a different box.

# ping 192.168.0.41
PING 192.168.0.41 (192.168.0.41) 56(84) bytes of data.
64 bytes from 192.168.0.41: icmp_seq=1 ttl=64 time=0.051 ms
64 bytes from 192.168.0.41: icmp_seq=2 ttl=64 time=0.061 ms
64 bytes from 192.168.0.41: icmp_seq=3 ttl=64 time=0.068 ms

Optional: remove dhcp clientIt may be necessary to remove the dhcp client in order to keep your IP address static. It seems that by default, dhcp3-client is setup to automatically renew it's lease 1 per day. You can remove dhcp3-client like this:

apt-get remove dhcp3-client