Troubleshooting routing

Unanswered Question

I have an odd routing problem. The route works great most of the time, but from time to time it seems the Cisco router losses its route to one destination.

I check the routing table and compare it with routing table before the outage and it they are the same, but when the packet comes into the ethernet interface, the router sends it to the default route (the firewall) instead of the correct route (serial interface).

Any ideas?

I have this problem too.
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Istvan_Rabai Tue, 10/21/2008 - 07:16

Hi Timothy,

What I would do to troubleshoot this is use the "debug ip routing" command.

I tell you why:

It can happen that there is a short route flap and you cannot catch this using the show ip route command during the outage.

"debug ip routing" will tell you if there is a short time route flap because it will debug route deletions and additions to the routing table.



With the use of the "debug IP rip" I was able to isolate the problem to a bad RIP update. Now I am trying to figure out where the bad update is coming from. I turned on "debug IP RIP event" and I am getting a lot of information. All I can do is wait to see where the update is coming from.

Any suggestions on best to isolate where the update is coming from?

Istvan_Rabai Tue, 10/21/2008 - 12:07

Hi Timothy,

In the output of the debug ip rip command you should be able to see which router the bad update is coming from.

Then debugging THAT router you can trace back from which router it receives the bad update and so on...

Finally you will get to the source.




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