Classful network

Since its discontinuation, remnants of classful network concepts have remained in practice only in limited scope in the default configuration parameters of some network software and hardware components, most notably in the default configuration of subnet masks.

The remaining 24 bits specified the local address, also called rest field (the rest of the address), which uniquely identified a host connected to that network.

As a consequence of this architecture, the address space supported only a low number (254) of independent networks.

The new addressing architecture was introduced by RFC 791 in 1981 as a part of the specification of the Internet Protocol.

The problem was that many sites needed larger address blocks than a Class C network provided, and therefore they received a Class B block, which was in most cases much larger than required.

Starting in 1993, classful networking was replaced by Classless Inter-Domain Routing (CIDR),[5][6] in an attempt to solve this problem.

[8] Class D is reserved for multicast and cannot be used for regular unicast traffic.