Spanning Tree loop - how to

[vincent-n]

I'd like to find out how to quickly identify a spanning tree loop problem on a standard/basic switch network. That is there is no QoS or CAR configured on the network, just simple basic setup such as VTP, root bridge, portfast.

It would also be appreciated if you can give some examples of how to quickly diagnose and rectify a loop problem. Thanks in advance for your comments.

[sachinraja]

hi vincent..

incase there are drops on your network or it functions crazy at times, you have to check your spanning tree states.. normally, spanning tree comes into picture only when your important trunks go down, to switch the packets to an alternate route ...

you can refer to the document below to diagonise and troubleshoot Spanning tree issues ...

http://cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800951ac.shtml

All the best !!

[milan.kulik · Accepted solution]

Additionally to the commands mentioned in the article:

sh spanning-tree detail

shows the number of TCNs:

"Number of topology changes 33 last change occurred 6w5d ago", e.g.

If you see highly increasing number of TCNs in your network, something goes wrong, probably.

There were also

sh diag addr-move

sh diag link-flap

useful commands available in the past.

But they seem not to be supported anymore (I don't understand why?).

Regards,

Milan