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EIGRP Meshiness

I attended the EIGRP Troubleshooting session in San Diego, and learned a lot - nice job.

After looking at our network here, and trying to apply some of the principles discussed regarding meshiness, I now have a quick question.

What makes an EIGRP query unique? Consider this - we have a pair of Cat 6509's with MSFC cards. There are a large number of shared VLAN's as this is a large campus network (there are actually 46 shared VLAN's between the switches and routers). If router A sees a link or other neighbor go down, and sends a query out all 46 interfaces to router B, what keeps router B from resending the query back to router A on the other 45 interfaces? Or does he send the query back to router A on the other 45 interfaces?

I got into a discussion with one of my associates, and he thinks that since the query is for a particular network, that makes the query unique and the routers will not send a query back to the neighbor.

Kevin Walsh

National Grid USA Services Company


Re: EIGRP Meshiness


Any interface that gets a query will reply. So all your 45 interfaces would generate a reply to this query and respond. The following is a very good URL for referrence on EIGRP function. Having 45 EIGRP neighbors is quite excessive. You might think about passive-interface on some of them since EIGRP can only use 6 paths at it's best anyway.

Hope this helps,


Community Member

Re: EIGRP Meshiness

Thanks Don ...

After attending the session, I realized that we needed to reduce the scope for EIGRP by setting most of the shared VLAN's to be passive.

My fear is that this mesh might cause an exponential explosion of messaging. Router B gets a query from Router A on 20 interfaces, and then forwards the query back to Router A on 19 interfaces, who then forwards the new query back to Router B on 19 interfaces - where does it stop? Or will the routers realize that this is the same query and only respond once.

I think I understand it better now. Thanks


Re: EIGRP Meshiness

Each router builds a query table to help it respond to each so no query loops a created. Hope this helps.


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