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New Member

EIGRP update, query

Studying for CCNP routing exam. Want to get this straight. Lets say a router loses an operational passive route and does not have a feasible successor in the topology table. It will then query its neighbors for a feasible successor. Will it also sent an update at that time because it lost a route?. Since the route is lost, another , if not numerous, devices must have noticed a link dropping within the network. Will they also be sending queries and then updates also in that order? Want to prepare for any scenerio questions of that type. Thanks.

5 REPLIES

Re: EIGRP update, query

It works as follows:

EIGRP behaves like a link-state protocol: It only sends updates when a connected link drops.

Remember all routers have an identical copy of the topology table. When a route disappears, this because of an update from another device states the route is no longer valid. The router does not have to send an update for this, the others know it already.

New Member

Re: EIGRP update, query

That is where I get confused. If the lost route traversed a directly connected link that went down, would the update follow the query or is it vice-versa? Or does it happen like that at all. Thanks.

New Member

Re: EIGRP update, query

Can anybody answer the above question. Thanks.

Silver

Re: EIGRP update, query

Have you looked at any of the EIGRP white papers on cisco's web site? For example, http://www.cisco.com/en/US/tech/tk648/tk365/technologies_white_paper09186a0080094cb7.shtml has a good explanation of how EIGRP works. In the case of your question regarding route queries versus route poisoning, the route poisoning is an automatic result of the route query.

Also, to correct the other posting, EIGRP is NOT a link-state protocol, but rather a distance vector protocol which maintains additional state information (compared to RIP) to allow it to recover quickly when known loop-free paths exist providing an alternate path when the preferred path fails. Unlike a link-state protocol, the topology table in each router is NOT identical, but rather is centered around that router. Consequently, the test for "loop-free" is a simple comparison based on route metrics rather than knowledge of the actual network topology.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

New Member

Re: EIGRP update, query

Thanks for the pointers. I am much clearer now that i have looked at that link. Have a nice one.

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