Internet Routing

Internet routing devices traditionally have been called gateways. In today’s terminology, however,
the term gateway refers specifically to a device that performs application-layer protocol translation
between devices. Interior gateways refer to devices that perform these protocol functions between
machines or networks under the same administrative control or authority, such as a corporation’s
internal network. These are known as autonomous systems. Exterior gateways perform protocol
functions between independent networks.
Routers within the Internet are organized hierarchically. Routers used for information exchange

within autonomous systems are called interior routers, which use a variety of Interior Gateway

Protocols (IGPs) to accomplish this purpose. The Routing Information Protocol (RIP) is an example
of an IGP.
Routers that move information between autonomous systems are called exterior routers. These
routers use an exterior gateway protocol to exchange information between autonomous systems. The
Border Gateway Protocol (BGP) is an example of an exterior gateway protocol.
Note Specific routing protocols, including BGP and RIP, are addressed in individual chapters
presented in Part 6 later in this book.