BPDU Guard: receive a BPDU on a (Port)Fast port → error-disable it. “No switches here.”
- Purpose: stop an access port joining the STP topology.
- Only makes sense with PortFast; never on uplinks.
- Fail-safe: dead port over loop.
BPDU Guard: receive a BPDU on a (Port)Fast port → error-disable it. “No switches here.”