Internet Routing Architectures, Second Edition

IP Address Space Depletion

The growing demand for IP addresses has put a severe strain on the classful model. Most companies requesting Class B addresses have estimated that a Class B address would best accommodate their requirements because of the balance between the number of networks and the number of hosts. A Class A was overkill, with more than 16 million hosts, and a Class C had too few hosts per network. By 1991, it was becoming obvious that the Class B consumption was not slowing and actions needed to be taken to prevent its depletion.

Some of the measures consisted of creative assignment of IP addresses and promoting the use of private addresses for organizations that did not have global Internet connectivity. Other measures resulted ...