stp loop, Not able to trace source

Unanswered Question
Oct 29th, 2007


I am new to cisco switches and learning about cisco switches now. we have a LAN with 6509 as core router and 2950s/3550s as access switches.

When I ran wireshark on my machine, I saw an stp loop repeating from a cisco device. I have noted down the MAC-address and tried in vain to find the same in our LAN. I am seeing packets like Address: "Spanning-tree-(for-bridges)_00" and "loop reply". I am not able to see any of the MAC addresses found in this loop conversation, on my LAN. I read that these loops are not good for the network. Where can I start to resolve this problem?

Thanks in advance for your advice.

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lgijssel Mon, 10/29/2007 - 00:54

There is likely no problem at all. ;-)

If you were really experiencing a loop, you would have other problems.

Best for you will be to start making a study of spanning tree (STP) and it's inner workings. Here is a good starting point:

Armed with this knowledge you can try to analyze the traffic that was observed by wireshark.



glen.grant Mon, 10/29/2007 - 16:36

That sounds like normal spanning tree bpdu traffic. If you had to you can probably debug spanning tree and see if anything strange is going on but I would use this with extreme care as certain debug functions can drive the CPU high .


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