Editing Classful network (section)

{{short description|Early system for organizing the IPv4 address space}}

[[Image:Internet map in February 82.png|thumb|300px|Map of the prototype Internet in 1982, showing 8-bit-numbered networks (ovals) only, interconnected by [[Router (computing)|router]]s (rectangles).]]

A '''classful network''' is an obsolete [[network address]]ing architecture used in the [[Internet]] from 1981 until the introduction of [[Classless Inter-Domain Routing]] (CIDR) in 1993. The method divides the [[IP address]] space for [[Internet Protocol version 4]] (IPv4) into five address classes based on the leading four address bits. Classes A, B, and C provide [[unicast]] addresses for networks of three different network sizes. Class D is for [[multicast]] networking and the class E address range is reserved for future or experimental purposes.

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 mask]]s.