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EIGRP problem

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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demon777
Asked:
demon777
1 Solution
 
shubhanshu_jaiswalCommented:
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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602650528Commented:
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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decoleurCommented:
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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rochey2009Commented:
It looks like a service provider problem.

Can you ping from one end of the link to the other?
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mikebernhardtCommented:
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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mikebernhardtCommented:
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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asavenerCommented:
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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rfc1180Commented:
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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demon777Author Commented:
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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mikebernhardtCommented:
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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demon777Author Commented:
None of the answers stated were correct.
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