IGRP Scalability Features
IGRP is an advanced distance vector protocol. Several features distinguish it from other distance vector routing protocols, such as RIP:
Increased scalability— Improved for routing in larger networks compared to networks that use RIP, IGRP can be used to overcome RIP's 15-hop limit. IGRP has a default maximum hop count of 100 hops, which can be configured to a maximum of 255 hops.
Sophisticated metric— IGRP uses a composite metric that provides significant flexibility in route selection. By default, internetwork delay and bandwidth are used to arrive at a composite metric. Reliability, load, and MTU may be included in the metric computation as well.
Multiple path support— IGRP can maintain up to six unequal-cost paths between a network source and destination, but only the route with the lowest metric is placed in the routing table. RIP, on the other hand, keeps only the route with the best metric and disregards the rest. Multiple paths can be used to increase available bandwidth or for router redundancy.
IGRP is a worthy candidate for IP networks that require a simple but more robust and scalable routing protocol than RIP Version 1 (RIP-1). Another advantage that IGRP has over RIP-1 is that it may be configured to perform triggered updates. It is important to point out that IGRP, even with advanced features, still uses techniques such as split horizon, hold-down timer (which is 280 seconds), and poison reverse updates to avoid routing loops