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.

This article needs additional citations for verification. (August 2022)

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:

• Routing Information Protocol (RIP)
• Routing Information Protocol Version 2 (RIPv2)
• Routing Information Protocol Next Generation (RIPng), an extension of RIP version 2 with support for IPv6
• Interior Gateway Routing Protocol (IGRP)

Examples of link-state routing protocols:

• Open Shortest Path First (OSPF)
• Intermediate system to intermediate system (IS-IS)

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).

• Route analytics