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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

6 comments

  1. hi,
    what happens to a port on which the ‘spanning-tree bpdufilter enable’ command was used if BPDU are received.

  2. There are 2 different actions which can happen (on a cisco device, that is), dependant on where it was configured.

    If you configure the feature globally, BPDU Filter applies to all PortFast-enabled ports, and if any configuration BPDUs are received on a PortFast-enabled port, the port immediately loses its PortFast status and returns to a normal STP port configuration.

    The Port-based BPDUFilter would just not send BPDUs and ignore received ones, thus most likely creating a switching loop, if there are switches behind it (the reason why there would be incoming BPDUs in the first place).

  3. Hi,
    according to Cisco Networking Academy Program:
    BPDU filter when enabled globally, it has these attributes:

    It affects all operational PortFast ports on a switch that do not have BPDU filtering configured on the individual port.
    If BPDUs are seen, the port looses its PortFast Status, BPDU filtering is disabled and STP sends and receives BPDUs on the port as any other STP port on the switch.
    Upon startup, the port transmits ten BPDUs. If this port receives any BPDUs during that time, PortFast and PortFast BPDU filtering are disabled.
    I want to focus on the last paragraph,what happen to a bpdufilter enabled port if it receives bpdu from another switch
    after ten BPDU transmission from a port under bpdufilter configuration.????

  4. Hi,
    I have a question. In interface level if we configure bpdufilter using the command: “spanning-tree bpdufilter enable” then could we disable the same using the command “spanning-tree bpdufilter disable” command at that interface or should we use the no form of the command i.e. “no spanning-tree bpdufilter enable”?

    Please let me know if there is any difference between them? And if there is then which works best?

  5. Question : What happens if I enable bpdufilter on a portfast port and it recieves a bpdu?
    Which answer is correct ?
    Ans 1 : It will disable portfast and participate in STP
    Ans 2: Since bpdufilter is enable on the interface directly, regardless of the portfast, it will not participate in STP.

    Whats the correct answer ?

  6. oi
    give answer

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