Internet addresses are divided in five distinct types of classes. The classes were designated A by E. class A address space lets a small number of networks although a large number of machines, whereas class C let for a large number of networks but a comparatively small number of machines per network. The below given figure lists five address classes utilized in classical network addresses.

Figure: The IP Address Structure

Regardless of the class of organizations assigned, address space assigned, a specific class of address will not utilize the whole address space provided. Especially this is in the case of class A & Class B address allocation schemes.