Interior Gateway Protocol (IGP) : A routing protocol that was designed and intended for use inside a single autonomous system (AS)
Known Interior Gateway Protocols (IGP) are Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS)
Exterior Gateway Protocol (EGP): A routing protocol that was designed and intended for use between different autonomous systems Exterior Gateway Protocol (EGP) is commonly used in the Internet to exchange routing table information. There is only one Exterior Gateway Protocol (EGP) exists and it is Border Gateway Protocol (BGP).