An interior gateway protocol (IGP) or interior routing protocol is a type of routing protocol used for exchanging routing table information between gateways (commonly routers) within an autonomous system (for example, a system of corporate local area networks).[1] This routing information can then be used to route network-layer protocols like IP.
Interior gateway protocols can be divided into two categories: distance-vector routing protocols and link-state routing protocols. Specific examples of IGPs include Open Shortest Path First (OSPF), Routing Information Protocol (RIP), Intermediate System to Intermediate System (IS-IS) and Enhanced Interior Gateway Routing Protocol (EIGRP).[2]
By contrast, exterior gateway protocols are used to exchange routing information between autonomous systems and rely on IGPs to resolve routes within an autonomous system.
Examples of distance-vector routing protocols:
Examples of link-state routing protocols:
Advanced distance vector routing protocols have both the features of distance vector routing protocols and link-state routing protocols. One example is Enhanced Interior Gateway Routing Protocol (EIGRP).