Traditional Class-based IP Version 4 Addressing

Each computer or device accessible using Internet (IP) protocols has at least one unique address within its subnet.

If every device was accessible over the global Internet, each device would require its own unique address (worldwide); each address consists of a network 'portion' and a local 'portion'. The network 'portions' are assigned by the central DARPA authority.

The original Internet designers were unsure as to how the Internet would grow - either a large number of networks each with a small number of hosts or a small number of networks each with a large number of hosts.

As a compromise, Internet addressing schemes accommodate both large and small network topologies.

Moreover, class-based addresses are self-describing.