Unanswered Question
Aug 15th, 2007


I need to know how we can chk for any broadcasts or loops occuring in the network with layer 2 access switches .

can anyone tell me if there is any specific commands like stp et al to chk the same.

i want to chk the same purely with cisco commands rather than using network tools.

and how can i isolate and regain the n/w after tht to normal.

thnks a ton in advance.

I have this problem too.
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tromer Thu, 08/16/2007 - 09:38

I cant think of a command perse, but you usually have some serious problems when there's a bridging loop. I would recommend going over your network diagram. Focus on the areas with redundancy where looping can occur. Then use your "show spanning-tree" commands and document your active spanning-tree.

I have seen switch lights go amber when there are loops. You can also check for interface errors.



Pavel Bykov Thu, 08/16/2007 - 10:32

You would have to check it manually. Ted suggested good commands.

Try the following:

1. Define domain where you want to troubleshoot, look for problems. (Could be VTP domain boundary, or VLAN boundary, etc.)

2. Check log for STP messages

3. Check intrface status for "Err-disable" state using "show interface status"

4. Check that there is only one ROOT BRIDGE for every VLAN (if you are running PVST) using "show spanning-tree vlan XXX", and looking where "ROOT" port leads.

Ports are:

EDGE P2P = hosts

P2P = switches further from root

ROOT = switches closer to root or root itself

You can also refer to this STP troubleshooting guide:

Hope this helps.

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