smothuku Tue, 12/30/2008 - 23:45
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Hi ,


BPDU guard is a feature that prevents a port from receiving BPDUs. This feature is typically used in a service provider environment where the administrator wants to prevent an access port from participating in the spanning tree. If the port still receives a BPDU, it is put in the ErrDisable state as a protective measure. This command has three states:

•spanning-tree bpduguard enable-This state unconditionally enables BPDU guard on the interface.

•spanning-tree bpduguard disable-This state unconditionally disables BPDU guard on the interface.

•no spanning-tree bpduguard-This state enables BPDU guard on the interface if it is in the operational PortFast state and if the spanning-tree portfast bpduguard default command is configured.


This example shows how to enable BPDU guard on this interface:

Switch(config-if)# spanning-tree bpduguard enable


spanning-tree portfast bpduguard default

To enable BPDU guard by default on all the PortFast ports, use the spanning-tree portfast bpduguard default command. To return to the default settings, use the no form of this command.

spanning-tree portfast bpduguard default

no spanning-tree portfast bpduguard default

Caution Be careful when using this command. You should use this command only with the interfaces that connect to the end stations; otherwise, an accidental topology loop could cause a data packet loop and disrupt the Catalyst 4500 series switch and network operation.


BPDU guard disables a port if it receives a BPDU. BPDU guard is applied only on ports that are PortFast enabled and are in an operational PortFast state.


This example shows how to enable BPDU guard by default:

Switch(config)# spanning-tree portfast bpduguard default


Cheers ,


wandering_997 Wed, 12/31/2008 - 01:59
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At least, they're in different command mode. :)

(config-if)#spanning-tree bpduguard enable

(config)#spanning-tree portfast bpduguard default

The 1st one enables bpduguard on the specified interface.

The 2nd one enables bpduguard on all interfaces which portfast is enabled.


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