IGP (Interior Gateway Protocol)
An IGP (Interior Gateway Protocol) is a protocol for exchanging routing information between gateways (hosts with routers) within an autonomous network (for example, a system of corporate local area networks). The routing information can then be used by the Internet Protocol (IP) or other network protocols to specify how to route transmissions.
There are two commonly used IGPs: the Routing Information Protocol (RIP) and the Open Shortest Path First (OSPF) protocol.
Also see the Exterior Gateway Protocol (EGP).