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The Routing Information Protocol (RIP) and Open Shortest Path First
(OSPF) are popular IGPs.
Internetwork routing has two dimensions: First, in the context of the
global Internet, internetwork routing is the exchange of routing
information between large, centrally administered networks known as
autonomous systems (ASs). A particular type of routing protocol
known as Exterior Gateway Protocol (EGP) performs this task. EGP
was the first protocol created to perform this function. Today, Border
Gateway Protocol (BGP) version 4 is the most commonly employed
protocol for this task. Refer to the section "TCP/IP Exterior Gateway
Protocols" later in this chapter for more information on EGP and
BGPv4.
The other, more useful dimension of internetwork routing is the
process of running multiple distinct routing protocol instances or a
collection of different IGP routing protocols to distribute routing
information within a network hierarchy. A common form of this model
is when a single root network acts as a common backbone, and child
networks branch off that backbone. The distinction between this type
of network from, say, an enterprise intranetwork is utilization of
different routing protocols within each child, so that each child
network administers its own routing policy (the function of deciding
what networks are available to the network and/or the scope of IP
network spaces that are managed under a single administrative
authority). The root network can act on behalf of all child networks in
the context of the global Internet.
NOTE
Under the OSI model, intranetwork routing is known as intradomain
routing.
NOTE
Under the OSI model, internetwork routing is known as interdomain
routing.