cat 6500s leave lots of forensic evidense of a bridge loop, only power down a switch as a last resort or it will be hard to track the source. The last loop we had on our huge 10G switch network was traced down to a VMWARE server that was misconfigured
With my experiance a bridge loops occurs and then SPT fails because the CPU spikes so fast, then no one is the root bridge, TCN's just keep looping and looping.
Steps to troubleshoot bridge loops or massive unicast flooding
Sho int | I tx|line
Shows all interfaces in switch with their corresponding tx and rx utilization. When there is a bridge loop you will see 100% utilization on at least 2 interfaces
Sho int | I output drops|line
Shows all interfaces in switch with their corresponding input queue drops and output drops. During a bridge loop you will see tons of output drops on the looping int
Sho spant det | I Number of top
Shows source of TCN origination
Switch#sho catalyst6000 all
chassis MAC addresses: 1024 addresses from 00d0.01e3.bc00 to 00d0.01e3.bfff
traffic meter = 1% Never cleared
peak = 40% reached at 11:32:30 AZ Wed May 10 2009
shows the last time there was a peak, after a loop condition has been corrected and you did not reload the switch you can or if your client claimed there was a loop and when you started working on the switch the loop was gone you can check this command, this peak will be high during a loop
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...