02-19-2019 08:19 AM - edited 03-08-2019 05:23 PM
I have (2) 2960XR's (Switch B) connected with a stacking module. They have port channels to (2) other 9500's (Switch A) in L3/L2 and another port channel to another (2) 2960XR's (Switch C) used as a access layer switch. One of the stacking modules in Switch B failed and both switches assumed the master role. Traffic through switch B was intermittent from switch A and C. It seems there was a loop, but I'm not sure how I can prevent this. We have spanning tree configured with loop guard.
02-19-2019 08:44 AM
02-19-2019 08:45 AM
If the stacking module failed then both switches in B are operating independently. And it certainly could create a loop. If we think about the individual members of B as B1 and B2 then think about this: A frame is received in B1 in vlan 2. It goes through the Etherchannel from B1 through switch A and is delivered to B2 and then is forwarded through the Etherchannel through switch C and delivered to B1 which detects the loop. As far as prevention is concerned I believe that your options are either to prevent the module failure/repair the module or to change the Etherchanels through A and C.
HTH
Rick
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