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03.05.07
IGRP And Equal Cost Load Balancing
 By
Chris Bryant
To pass the CCNA exam, you've got to know the role of the bandwidth command with IGRP and EIGRP and when to use it.
In this tutorial, we'll configure IGRP over a frame relay hub-and-spoke network using the following networks:
R1 (the hub), R2, and R3 are running IGRP over the 172.12.123.0 /24 network. This is a T1 line.
R1 and R3 are also connected on a different subnet, 172.12.13.0 /24. The bandwidth of this connection is 512 KBPS.
R2 and R3 are also connected by an Ethernet segment, 172.12.23.0 /24.
We'll configure IGRP on R1, R2, and R3 with the router igrp 1 command. IGRP will run on all interfaces in the 172.12.0.0 and 172.23.0.0 network.
R1#conf t
R1(config)#router igrp 1
R1(config-router)#network 172.12.0.0
The "1" in the router igrp command refers to the Autonomous System (AS). IGRP is a classful routing protocol, so wildcard masks are not used in the network statements.
R2#conf t
R2(config-if)#router igrp 1
R2(config-router)#network 172.12.0.0
R2(config-router)#network 172.23.0.0
R3#conf t
R3(config-if)#router igrp 1
R3(config-router)#network 172.12.0.0
R3(config-router)#network 172.23.0.0
Run show ip route on R1. R1 will see three equal-cost paths to the Ethernet network. IGRP supports load-sharing over up to four equal-cost paths by default, so all three paths appear in the routing table. R1 will also see a route to the loopback address on R2 and two routes to the loopback address on R3. (You can also run show ip route igrp in order to see only the IGRP routes.)
Continue reading this article.
About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage (www.thebryantadvantage.com), home of FREE CCNA and CCNP tutorials and daily exam questions, as well as The Ultimate CCNA and CCNP Study Packages.
For a FREE copy of his latest e-books, "How To Pass The CCNA" or "How To Pass The CCNP", and for free daily exam question, visit the website and download your copies!
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