Chapter 4. Understanding Interior Gateway Routing Protocol (IGRP)

This chapter covers the following key topics about Interior Gateway Routing Protocol (IGRP):

• Metrics

• Timers

• Split horizon

• Split horizon with poison reverse

• IGRP packet format

• IGRP behavior

• Default route and IGRP

• Unequal-cost load balancing in IGRP

In the mid-1980s, Cisco developed its own proprietary routing protocol, Interior Gateway Routing Protocol (IGRP), as a solution to some of the shortcomings of RIP, such as the hop-count limitation of 15.

Like RIP, IGRP is a distance vector protocol. However, IGRP calculates its composite metric from a variety of variables, such as bandwidth and delay, and hop count is not considered in the routing decision. IGRP uses variables ...

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