Editing Classful network (section)

==Background==
In the original address definition, the most significant eight bits of the 32-bit IPv4 address was the ''network number'' field which specified the particular network a host was attached to. 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.{{Ref RFC|760|section=3.1}} This format was sufficient at a time when only a few large networks existed, such as the [[ARPANET]] (network number 10), and before the wide proliferation of [[local area network]]s (LANs). As a consequence of this architecture, the address space supported only a low number (254) of independent networks.

Before the introduction of address classes, the only address blocks available were these large blocks which later became known as Class A networks.<ref>{{Cite IETF
 | ien = 46
 | title = A proposal for addressing and routing in the Internet
 | first = David D. | last = Clark
 |date=June 1978
 | publisher = [[IETF]]
 | access-date = 2014-01-08
}}</ref> As a result, some organizations involved in the early development of the Internet received very large address space allocations (16,777,216 IP addresses each).