Anton sent me an interesting question:
Most IP phones have a network facing port and a port for user to connect the PC. Today a user plugged in both of these ports into the switch. It looks like phone filters out BPDUs, so the switch did not catch this loop. Do you know of a feature or design that would be able to catch/prevent this type of event?
My answer would be “no, there’s nothing you can do if you have a broken device that acts like a STP-less switch” but you know I’m not a switching or IP telephony guru. Any ideas?