This topic is to discuss the following lesson:
Can u explain me what is the problems of EIGRP Query msg?
When an EIGRP router sends a query to a neighbor it will expect a reply. If it doesn’t get a reply within a certain amount of time than it will clear the EIGRP neighbor adjacency with that neighbor.
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Very nice lesson, well explained
Keep it up
thanks alot
thanks… now i understand!
well said
thanks a lot sir , words can’t describe your efforts
Another fun command is “eigrp kill-everyone” under the EIGRP process which, in the case of SIA, will clear ALL EIGRP neighbors.
Hi Rene! I have a question. If a router, after sending query messages to its neighbors, receive reply with route from first router, but doesn’t receive any reply from second router will route be in stuck in active or not? I ask because in fact router already have valid route which has been received from first router.
What happens to the lost route after SIA query and SIA reply?
When one of the routers does have information about the lost route then it will inform its neighbor. When nobody knows about the lost route, it will be removed from the topology table eventually.
Nic explanation 
I have a question related to the congestion of the last example. Before the 7 or rather 8 steps, you explained that there could be 3 problems with a reply. In your example you have showed a problem with a reply from Router 2 to Router 1. Alright until then, but is it just a permanent problem between Router 1 and his first neighbor and his reply or could it has been successful and there would have been no problems at all? Moreover could the problem with the reply be from Router 3 to Router 2 (reply) also? And why there is a congestion?
Probably I’ve understood it, since I haven’t watched your video before asking the question. Let me try: There is no permanent problem between Router 1 and his neighbors, since this was just an example from you. Moreover there still could be a problem with a query between Router 3 and Router 2 (theres none in your example but it could happen). Nevertheless I barely unterstand the “congestion” part?!
Hi Sascha,
When an EIGRP router loses a successor and doesn’t have any feasible successors, it will send a query to its neighbor. When this neighbor doesn’t know the answer, it will also start sending queries to its neighbors. When EIGRP sends a query, it HAS to get a reply back. If you don’t get a reply…we kill the EIGRP neighbor adjacency.
The reason why a reply doesn’t make it back is probably temporarily, a router could be overburdened (high CPU load) and not able to process the reply or unable to create a query.
Interfaces have a certain bandwidth and when there’s more traffic than the interface can handle, it will be dropped…this is congestion. It’s possible that an EIGRP query or reply doesn’t make it because of congestion.
This “query sent - no reply back” problem can occur everywhere, also between R2-R3. If R2 sends a query and doesn’t get a reply from R3 then it will drop it as an EIGRP neighbor…
Does this help?
Rene
That’s right. Queries & replies that don’t make it back is probably a temporarily problem…high CPU load or congestion. If there would be a permanent problem with the connection between two routers then probably the EIGRP hello packets also won’t make it through…as a result the neighbor adjacency will drop.
This post should give you a better idea of what congestion is:
Rene
What are some ways to troubleshoot this during production hours?
Thanks in advance!
Hi Sean,
This will only occur when EIGRP loses a network so I would start looking for flapping interfaces and flapping EIGRP neighbor adjacencies.
Rene
great explanation ,thank you.