IP Routing Fundamentals

The Emergence of Subnetworks

The Internet's original two-level hierarchy assumed that each site would have only a single network. Therefore, each site would only need a single connection to the Internet. Initially, these were safe assumptions. Over time, however, networked computing matured and expanded. By 1985, it was no longer safe to assume that an organization would only have a single network, nor would be satisfied with a single connection to the Internet.

As sites began to develop multiple networks, it became obvious to the IETF that some mechanism was needed to differentiate between the multiple logical networks that were emerging within sites of the Internet's second tier. Otherwise, there could be no efficient way to route data to ...