Interior Gateway Routing Protocol
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Interior Gateway Routing Protocol (IGRP) is a proprietary distance-vector routing protocol invented by Cisco, used by routers to exchange routing data within an autonomous system.
IGRP was created in part to overcome the limitations of RIP (maximum hop count, and a single routing metric) when used within large networks. IGRP supports multiple metrics for each route, including bandwidth, load, delay, and reliability; to compare two routes these metrics are combined together into a single metric, using a formula which can be adjusted through the use of pre-set constants. The maximum hop count of IGRP-routed packets is 255.
Its successor is EIGRP, an advanced distance-vector routing protocol, that uses many features of link-state protocols, and adds Diffusing Update Algorithm (DUAL) ideas to the basic distance-vector mechanism of IGRP.