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 betweenAutonomous 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
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