“Something else to note: Classful IP addresses used in Class A, B, and C are not quite as necessary anymore. In fact, many corporate networks use classless IP addressing. This means that any network number can use any subnet mask. (Breaking all the rules!) For example, one of my test networks uses the 10.254.254.0 network and the 255.255.255.0 subnet mask, making the network number 10.254.254, instead of just 10. How is this done? By changing the subnet mask to 255.255.255.0 instead of the default 255.0.0.0. (I guess this means my test network has no class. Ouch!) Seriously though, this method is known as Classless Inter-Domain Routing, or CIDR for short, and you will deal with this more if you decide to enter into the realm of Network+.”