Chapter 6. Interior Gateway Routing Protocol (IGRP)
Operation of IGRP
IGRP Timers and Stability Features IGRP Metrics IGRP Packet Format
Configuring IGRP
Case Study: A Basic IGRP Configuration Case Study: Unequal-Cost Load Balancing Case Study: Setting Maximum Paths Case Study: Multiple IGRP Processes
Troubleshooting IGRP
Cisco developed
IGRP in the mid-1980s as an answer to the limitations of RIP, the most important of which are the hop count metric and the 15-hop internetwork size. IGRP calculates a composite metric from a variety of route variables and provides "knobs" for weighting the variables to reflect the specific characteristics and needs of the internetwork. Although hop count is not one of these variables, IGRP does track hop count and can be implemented on internets of up to 255 hops in diameter.
IGRP's other advantages over RIP are unequal-cost load sharing, an update period three times longer than RIP's, and a more efficient update packet format. The chief disadvantage of IGRP is that it is proprietary to Cisco and therefore limited to Cisco products, whereas RIP is a part of any IP routing process on any platform.
Cisco's objective when developing IGRP was to create a versatile, robust protocol capable of being adapted to a variety of routed protocol suites. Although it has proven to be a very popular routing protocol for IP, IGRP has been adapted to only one other routed protocol, the ISO Connectionless Network Protocol (CLNP).See the Cisco configuration manuals for more information
on routing CLNS with IGRP.
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