The Interior Gateway Routing Protocol (IGRP) is a distance-vector routing protocol developed by Cisco for use within an autonomous system. It helps routers communicate and share information about network paths, allowing them to determine the best routes for data packets. IGRP uses metrics such as bandwidth, delay, load, and reliability to make routing decisions. IGRP is designed to support larger networks and can handle up to 255 hops, making it suitable for complex topologies. However, it has been largely replaced by more advanced protocols like Enhanced Interior Gateway Routing Protocol (EIGRP) and Open Shortest Path First (OSPF) due to their improved efficiency and scalability.