Here are the steps for adding and removing an alias to a NIC on a FreeBSD 8.x machine.

 

Find out the name of the NIC :

# ifconfig

 

As you’ll see from the above screenshot the NIC is called em0

Now to add the alias:

# ifconfig em0 192.168.9.50 netmask 255.255.255.0 alias

 

Note: To remove the alias:

# ifconfig em0 192.168.9.50 netmask 255.255.255.0 delete

 

You can check this at any stage by issuing the following command

# ifconfig em0