STP Discarding Packets from the Switch Port

[krunal]

How to resolve this?

[KarstenI]

• What is connected to this port?
• What is the STP-Config for this port?

[cmr]

Is the device connected to this port also connected to the switch via another route?  If so then spanning tree blocks one of the routes, usually the highest cost, based on number of hops, speed and port number.

[PhilipDAth]

99.9%, this means you have a layer 2 loop.  This switch has 2 (or more connections) to whatever connects to this port.  It could also have a loop indirectly via another device (especially in a switch static, but not exclusively so).

[prabhulkars]

Does the error follow if the device is connected to a different port? If you have a non-Meraki Switch connected see if the STP priority and also check on the dashboard which switch is elected as the Root Bridge. The error occurs when the switch is receiving unexpected BPDU packets from the port a.k.a. detecting loop.

[GIdenJoe]

Yes this port is an alternate port.
This means you will be having inbound BPDU's.

If you want to check where the BPDU's are coming from you can do a packet capture on the port filtering for: ether host 01:80:c2:00:00:00 and let it run for 30 seconds so you can gather all BPDU's.

The bridge ID of the incoming BPDU should give you a clue from what the device the frame is coming from.