Hierarchical routing
Appearance
Hierarchical routing: Routing that is based on hierarchical addressing.
Note: Most Transmission Control Protocol/Internet Protocol (TCP/IP) routing is based on a two-level hierarchical routing in which an IP address is divided into a network portion and a host portion. Gateways use only the network portion until an IP datagram reaches a gateway that can deliver it directly. Additional levels of hierarchical routing are introduced by the addition of subnetworks.
Source: From Federal Standard 1037C
External Link - http://www.isi.edu/nsnam/ns/doc-stable/node310.html