debug spanning-tree bpdu brought the network down

[hypnotoad]

I'm troubleshooting a pair of Dell Power-Connect switches in a Dell blade chassis connected to a pair of Cisco 4900M switches. I have my 4900M switches set as spanning-tree root and backup root. The Dell switches are connected via LACP trunks to the 4900M's. Dell switch 1 to 4900 #1 and Dell switch 2 to 4900M #2. Both of the Dell switches are reporting as root switches.

I was trying to troubleshoot this yesterday and ran 'debug spanning-tree bpdu' on the primary 4900M. There was a masive amount of BPDU events scrolling by. This debug command actually took the network down. The primary 4900M was non-responsive and the secondary unit had it's CPU go to 100%. The fix was to power cycle the primary 4900M.

Why did this command take my network down?

--Patrick

[Jon Marshall]

Patrick

Were you logged in via the console ?

Jon

[hypnotoad]

I was logged in via SSH and used 'term mon' to show the console..

--Patrick

[Ri0N]

Typically, the device prioritizes console output ahead of other functions. The debug spanning-tree bpdu generates a lot of output. That is what jumped the CPU to 100% and ultimately caused the device to crash.

You should be very careful with debug commands and log to the internal buffer, instead of the console.

See: http://www.cisco.com/c/en/us/support/docs/dial-access/integrated-services-digital-networks-isdn-channel-associated-signaling-cas/10374-debug.html.