Configuring BPDU filtering

The STP BPDU filter feature allows control of spanning tree participation on a per-port basis. It can be used to exclude specific ports from becoming part of spanning tree operations. A port with the BPDU filter enabled will ignore incoming BPDU packets and stay locked in the spanning tree forwarding state. All other ports will maintain their role.


spanning-tree [port-list | all] bpdu-filter
no spanning-tree [port-list | all] bpdu-filter

Enables or disables the BPDU filter feature on specified port(s). This forces a port to always stay in the forwarding state and be excluded from standard STP operation.

Sample scenarios in which this feature may be used are:
  • To have STP operations running on selected ports of the switch rather than every port of the switch at a time.

  • To prevent the spread of errant BPDU frames.

  • To eliminate the need for a topology change when a port's link status changes. For example, ports that connect to servers and workstations can be configured to remain outside of spanning tree operations.

  • To protect the network from denial of service attacks that use spoofing BPDUs by dropping incoming BPDU frames. For this scenario, BPDU protection offers a more secure alternative, implementing port shut-down and a detection alert when errant BPDU frames are received.


Ports configured with the BPDU filter mode remain active (learning and forward frames); however, spanning tree cannot receive or transmit BPDUs on the port. The port remains in a forwarding state, permitting all broadcast traffic. This can create a network storm if there are any loops (that is, trunks or redundant links) using these ports. If you suddenly have a high load, disconnect the link and disable the bpdu-filter (using the no command).

Configuring BPDU filtering

To configure BPDU filtering on port a9, enter:

switch(config)# spanning-tree a9 bpdu-filter