IGRP

Jul 05, 2008 @ 05:17 pm by HackingManual

IGRP stands for Interior Gateway Routing Protocol.

IGRP is a distance vector protocol, meaning that it decides that the best path is the closest path. IGRP sends regular updates to it’s neighbors but it doesn’t talk as much as RIP. IGRP updates every 90 seconds. Because RIP couldn’t handle long distance relationships IGRP was created as a replacement. IGRP’s Default hop count is 100 but it can be set up to 255 hops by the network administrator. Which is way further than RIP’s 16 hop maximum.

RIP also lacked more than one routing metric. IGRP uses Bandwidth, Delay, reliability, and load as it’s routing metrics.

IGRP is a Cisco proprietary protocol. Meaning it only talks to routers made by Cisco. Kinda like the preppy girls from high school who wouldn’t be caught dead talking to someone who wasn’t popular.

IGRP uses hold down timers prevent gossip. When a route is marked invalid hold down timers prevent router gossip from reinstating that route. So lets pretend we have a router named Map , so if Map doesn’t receive an update from a particular route with in a certain period of time, it calculates the next best way to get to the destination, then it sends that information to all of the other routers. Then those routers update everyone else. The failed route change gets spread by word of mouth so to speak. But what if a router that hadn’t gotten an update and spreads false information to a router that had gotten the update. When a route is marked invalid, hold down timers prevent router gossip from reinstating that router. IGRP also uses split horizons and poison reverse to prevent routing loops.

Uses AS Number for activation
Invalid Timer: 270 seconds or 3 times how often it updates.
Hold down Timer: 280 seconds or 10 seconds more than the invalid timer.
Flush timer: 670 seconds or 7 times how often it updates.

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