Skip the gui and do it via command line.
The following link provides detailed information on how to create the alias on a temporary basis, as well as how to edit the interfaces file to make the change permanent.
Information from site in case of site death:
ifconfig command line
You can use ifconfig command to configure a network interface and alias. For example:
- eth0 NIC IP 192.168.1.5
- eth0:0 first NIC alias: 192.168.1.6
To setup eth0:0 alias type the following command as the root user:
# ifconfig eth0:0 192.168.1.6 up
Verify alias is up and running using following command:
# ifconfig -a
# ping 192.168.1.6
However, if you reboot the system you will lost all your alias. To make it permanent you need to add it network configuration file.
# vi /etc/network/interfaces
Append the following to the file (This is in addition to existing information, not a replacement for it)
iface eth0:1 inet static
name Ethernet alias LAN card
Save and close the file. Restart the network:
# /etc/init.d/networking restart