Additional information is that we have 2 sups in the chassis. The 1st floor uses 5/1 and the 2nd floor uses 6/1. The sups are configued in SSO, so module 6 is in standby. The 5/1 port shows bpdus being sent and the switch on the other end shows bpdus being received (Dell switch on other end), whereas 6/1 shows bpdus being sent but none received on the other end (Dell switch). Does STP run normally over a standby SUP?
Even though the Sup in slot 6 is in standby, its interfaces are still operational. You can verify this with "show int status mod 6"
Next verify the STP role and status of the interface with "show spanning-tree int 6/1". You can add "active detail" at the end of that command to check the BDPU counters, but sounds like you already did that.
Is the Dell switch acting as STP root? If so, it would not bother to receive BPDUs.
I vaguely remember trying to debug STP BPDUs a couple years ago and having the same problem. Hmmm...
Oh yeah - have you looked in to the storm control message from Gi2/48 and 3/48? It may indicate an STP loop, which would drive up the CPU and perhaps interfere with the debugging messages showing up. Just a thought.
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