For the past 3 months, we encountered switching loops twice in our network bringing down the whole system and we cannot trace what's causing it. Our core is running 6500 Sup2 (hybrid) and all the distribution/access switches are 4500 and a one 3750 stack (4 switches). All distribution/access switches are connected to those 2 6500 switches for redundancy and the core switches have etherchannel trunk in between using Gi1/1 and Gi1/2 ports. Two months ago when the first incident happened, the GBIC ports on both core switches randomly transitioned to UDLD err-disabled state. Fortunately we are running UDLD err-disable recovery feature. That thing happened the day after I installed the 3750 Stack into the network.
Now the network behavior is abnormal. The distribution/access switches transitions to loopguard or UDLD state randomly.
When I talked to our MA Vendor, she mentioned (the engineer) that there was an incident before that she handled where a 3750 stacked switches brought down a network.
Anyone of you experienced this? Thanks.