A
routing protocol specifies how routers communicate with each other,
disseminating information that enables them to select routes between any two
nodes on a computer network. Routing algorithms determine the specific choice
of route. Each router has a priori knowledge only of networks attached to it directly.
A routing protocol shares this information first among immediate neighbors, and
then throughout the network. This way, routers gain knowledge of the topology
of the network.
Although
there are many types of routing protocols, three major classes are in
widespread use on IP networks:
Interior
gateway routing via link state routing protocols, such as OSPF and IS-IS
Interior
gateway routing via distance vector routing protocols, such as RIPv2, IGRP and
EIGRP
Exterior
gateway routing. The Border Gateway Protocol (BGP), a path vector routing
protocol, is the routing protocol used on the Internet for exchanging traffic
between Autonomous Systems.
Some
versions of the Open System Interconnection (OSI) networking model distinguish
routing protocols in a special sublayer of the Network Layer (Layer 3).
The specific
characteristics of routing protocols include the manner in which they avoid
routing loops, the manner in which they select preferred routes, using
information about hop costs, the time they require to reach routing
convergence, their scalability, and other factors
