IGRP Facts

Interior Gateway Routing Protocol (IGRP) is an improvement on RIP, but just barely. I have never seen it in use in the field, nor have I ever read someone claiming that IGRP is the best protocol for a specific purpose. Basically, it is an option on Cisco routers so you need to know about it if you are studying for certification, but you will probably never need this information in real life.

Real world routing protocol advice: if you have a small, simple network use RIP to dynamically share routing information among routers. If you have a large, complex network and/or security is a concern, use EIGRP. The other protocols (IGRP, OSPF, and IS-IS) are just about worthless in comparison to RIP and EIGRP. The only caveat to this is if you are connecting your network to a non-Cisco powered network. In that case, your routing protocol will be dictated by the capabilities of the neighbor router, and OSPF may be your best choice here. Let's hope that never happens to you.

IGRP Facts

I just want to share a few quick facts about IGRP that you may not know which will help when you sit for a Cisco certification:

-The components of the IGRP routing metric are bandwidth, delay, reliability, load, and MTU.

-IGRP differs from rip because IGRP is more suitable for large networks, it uses a more flexible metric for route selection, and it can select multiple non-equal paths to a destination.

-When you configure IGRP for un-equal cost load-balancing, you must observe several rules. First, The maximum paths you can set is 6. Second, The next-hop must be closer to your destination than the local router, according to the local router's best path. Third, the alternate path metrics must be within a specified variance of the best local metric.