Potential network looping?

[riderfaiz]

Hi everyone,

Good morning! Hope you can help on this... I never imagine this (may) happen to me here....

I barely pay attentions but couple months ago I realized all the connected-port lights on Csico switches are flashing simultaneously. Most of the switches have STP. I also tried shutdown switches one by one to see any difference but no luck.

To identify the problem, what should I do, and which command(s) I should use? Some people said I should check the port utilization...  Now I just clear the counter of all switches. I will check on any ports which more than one Mac addresses. I will also review the config on those new switches added to the network (not too many).

If you have any suggestions to work on this issue.. that would be great.

Thank you for your help in advance.

Takami Chiro

[balaji.bandi]

All light flashing ? what Switch ?  if it layered network, if not many.

1. check the Logs on all the switches

2. check show spanning-tree

3. shutdown one by one link going down toward access switches -  check which one culprit.

[riderfaiz]

Thank you for your response. I really appreciate it.

For check log and spanning tree. which specific info I need to look for to show there may be a sign of network loop/broadcast storm?  did try to reboot the switch one by one by no luck to narrow down witch switch causing the problem. 

Please advise. Thank you!

Takami Chiro

[balaji.bandi]

Mainly you need to look at the Network diagram  check is there any L2 dual links connected in the network. how is your spanning-tree configured or did you enable spanning-tree guard, and portfast on access ports

[paul driver]

Hello

Do you a extended Layer2 network, is spanning tree enabled for all your vlans?
Would suggest enable spanning tree for all vlans, Apply stp portfast and bpduguard on all access-ports and manually prune unwarranted vlans of your trunk ports