Had a strange issue where we had some Avaya IP Phones dropping off the network (losing DHCP IP) which I tracked down to an issue caused by an IP Phone causing an STP loop.
Often in meeting rooms uneducated users patch the IP Phone downlink cable back into spare network ports that are part of the meeting room which creates a loop due to the mini-switch that is part of the IP Phone.
BPDU Guard picks this up and disables the port, but I had also configured errdisable recovery so we don't end up with lots of dead ports. During this period of recovery, which tempoariliy creates a loop until BPDU Guard disables the ports, I was seeing massive drops on the majority of interfaces on the 4500E switch. These drops were predominantly Belligerent Flow Drops (Dbl-Drops-Queue-8) in the class-default class which has DBL applied (we are running AutoQos on the WS-X45-SUP7-E).
I guess QoS picks up this traffic and drops it as a safety mechanism for the voice traffic.
Anybody seen this behavour before?
I have disabled errdisable recovery in the meantime which has stopped the drops, but means more manual work to re-enable dead ports after user patching errors. Any other workarounds?