What is: BPDU filter?

BPDUs are the messages exchanged between switches to calculate the spanning tree topology. BPDU filter is a feature used to filter sending or receiving BPDUs on a switchport.

It is extremely useful on those ports which are configured as portfast ports as there is no need to send or receive any BPDU messages on of these ports.

BPDU filter can be configured globally or under the interface level. When configured globally all portfast enabled ports stop sending and receiving BPDUs, but if a BPDU is received on the port it gets out of the portfast state and normally participate in the spanning tree calculations.

Global mode configuration:

spanning-tree portfast bpdufilter default

Enabling BPDU filtering in the interface level stops sending or receiving BPDU on this interface; this is the same as disabling spanning tree on the interface. This is a risky choice unless you are sure that no switch can ever be connected to this port.

Interface mode configuration:

spanning-tree bpdufilter enable

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