"debug spanning-tree bpdu" ... where are the 802.1d bpdus from the root?

Unanswered Question
Sep 5th, 2009


My test lab works fine, but when I do a

"debug spanning-tree bpdu"

I never see bpdus of the root bridge in my logs.

I have tried it out with a C3750 and a C3550 as a root bridge, but it is always the same.

If any one could help me - that would be great! :-)

Best regards from Austria,


I have this problem too.
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Giuseppe Larosa Sat, 09/05/2009 - 11:04

Hello Silvia,

first of all great caution with this debug: never use it on production network.

I did and I was lucky to find someone to reboot the switch (a C4506) it has become unmanageable in a few seconds and also user traffic had started to be affected.

So use it only in a lab.

Some debug commands show only received packets of a certain protocol for example STP and the root bridge receives BPDUs only when a topology change happens.

do you see root bridge BPDUs on non-root bridge when using the debug?

Hope to help


silvia.schuckert Sat, 09/05/2009 - 12:11

Hi Guiseppe!

Thank you for the answer and the hint!

But I am luckily in the lab.

That's exactly what I could see.

I see outgoing config bpdus from all switches (except the root).

As soon as Topology Changes happen - I see more.

So there is no way to change that? I was wondering, because there would be a further debug command "received" "send" that I didn't use.

When I see in the logs "Data 000000*" is this the received or the sent Data?



Giuseppe Larosa Sat, 09/05/2009 - 12:34

Hello Silvia,

I can only look at the debug command reference that you can find here:


Actually, it declares that both received and sent BPDUs should be seen in the debug output.

It also provides two options: transmit and receive.

So you have found a different behaviour on STP root bridge.

I would suggest to use STP commands to make different switches root bridges in different vlans and to see what happens.

Hope to help



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