Open /etc/network/interfaces

Example of the file is below:

Code:
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
        address 207.210.118.56
        netmask 255.255.255.224
        broadcast 207.210.118.63
        network 207.210.118.32
        gateway 207.210.118.33
Add a new line

Code:
auto eth0:1
below
Code:
auto eth0
and new interface description

Code:
iface eth0:1 inet static
        address 207.210.118.58
        netmask 255.255.255.224
        broadcast 207.210.118.63
        network 207.210.118.32
        gateway 207.210.118.33
Make sure that the mask and gateway is correct.

The resulting file would look like this:

Code:
auto lo
iface lo inet loopback

auto eth0
auto eth0:1
iface eth0 inet static
        address 207.210.118.56
        netmask 255.255.255.224
        broadcast 207.210.118.63
        network 207.210.118.32
        gateway 207.210.118.33
iface eth0:1 inet static
        address 207.210.118.58
        netmask 255.255.255.224
        broadcast 207.210.118.63
        network 207.210.118.32
        gateway 207.210.118.33
When this done execute

/etc/init.d/networking restart