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EIGRP problem

Posted on 2011-03-17
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Last Modified: 2012-05-11
At work I look after 4 data centres, with a router utilizing 4/4 IPMAN cross connects. Each of these routers has atleast one link to this IPMAN, over which we run EIGRP as the IGP.

Now everything had been working fine till a few months ago, when one of the links, connecting Colo B ---- Colo C went down. I noticed the EIGRP neighbor relationship was no longer forming on Colo C side (nothing in the debugs) and on Colo B side the neighbor as Colo C would show up, RTO would expire, and it would go down/up again. We tried everything (link speeds, duplexes, EIGRP statements, no static routes) - but resigned it as a hardware/link fault which we would need to chase up with the IPMAN provider.

A few months down the line, everything was working fine but yesterday the neighbor relationship between Colo B ---- Colo D went down. The issue was exactly the same, this time no debugs or neighbors (with Colo D) showing up on Colo B , and Colo D keeps trying to form a relationship with Colo B, times out, and starts over again.

This is pretty strange and since Colo B --- Colo D link is critical for business operation, I am keen to figure out the cause of this.  Currently i'm routing the traffic through another router with static routes and all is well, but would love some feedback to see what your opinions are. Is it a link fault? Is there anything I could do to confirm this?

There are no CRC/errors on the actual interfaces, the routers are all fine with rest of the links working well. No duplex/speed issues as this was working well just yesterday.

Appreciate all the comments guys.
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Question by:demon777
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by:shubhanshu_jaiswal
ID: 35165056
It is very hard to visualize the topology from the written description..could you please post a diagram which will show all the routers involve in the EIGRP Process...
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by:602650528
ID: 35166001
Hi demon777,

Eigrp is very finicky about MTU size and the problem doesn't show up immediately. I strongly suspect this issue has to do with different mtu size on the interface of the eigrp neigbours. Can you check the mtu size and make sure they are same across a link between neigbours.
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by:decoleur
ID: 35166232
what do the debugs show you during these failures? capture them from both sides with a common time source and see if that doesn't help.

-t
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by:rochey2009
ID: 35166922
It looks like a service provider problem.

Can you ping from one end of the link to the other?
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by:mikebernhardt
ID: 35166953
Colo B has no debugs at all? There's got to be something, unless the appropriate interface is not part of the EIGRP process anymore. If you can post the EIGRP config and the appropriate interface config from both sides, that would help.
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by:mikebernhardt
ID: 35166970
Also, remember that in a multipoint configuration on subinterfaces (if you have that), you may need to enter neighbor statements since multicast doesn't work well.
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by:asavener
ID: 35167775
I've seen EIGRP fail to establish neighbor relationships dynamically, but adding neighbor statements will cause the relationship to start working.

Have you tried adding static neighbor statements?
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by:rfc1180
ID: 35172665
If you seriously want help with the issue you are going to have to post your configs and provide a detailed network diagram. It is really hard to comment on your issue as what you are experiencing could be related to just about anything. If you cannot provide this information, I would then recommend that you hire a engineer in your local area that can assist, what you describe can be a lengthy process to diagnose the issue.

Billy
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demon777 earned 0 total points
ID: 35228279
Sorry to update this late guys, unfortunately none of the answers were correct.
The router dropped two more neighbours and had to be finally rebooted, and all neighbours came back online. It was indeed a hardware issue and we will be looking at replacing this router sometime in the future.

We've had MTU issues in the network and all interfaces operate on a standardized size. Static neighbour statements were not an issue as other neighbours in the same range were forming a relationship fine, over the same common IPMAN link.

Debugs on the other end showed nothing (yes, nothing!) which was what was weird about the whole thing - well its all good now thank you for the answers.
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by:mikebernhardt
ID: 35243349
Most likely it's not a hardware issue, but an IOS software issue. You might look into upgrading the software with the latest maintenance release.
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by:demon777
ID: 35292532
None of the answers stated were correct.
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