At some point you may be interested in building a firewall for your dedicated server that you lease from a hosting company. Once you do that you will be faced with trying to work with the assigned IP Addresses to the server. Typically hosting companies will assign a subnet and use aliases for the one Ethernet card that is used on the server. It will look something like what you see in the image below. The problem is, iptables will not recognize aliases for the Ethernet card.