Internet address classes

Internet address classes are defined to segment the available address space into networks of different sizes. Classes A, B, and C are reserved for unicast communication, D is reserved for multicast addresses, and the E class is reserved for experimental uses. The addressing scheme where classes are used is called classful.

Furthermore, the term subnet mask describes which bits of an address define the network ID, and which bits represent the host ID.

The following table presents the default subnet masks and address classes: