Cisco Systems OL-4580-01 manual Enabling Port Fast, Enabling Bpdu Guard

Chapter 1 Configuring Interfaces and Circuits

Configuring Interfaces

Enabling Port Fast

A port with the Port Fast feature enabled is moved directly to the spanning-tree forwarding state without waiting for the standard forward-time delay.

Caution Use Port Fast only when connecting a single end station to a CSS interface. Enabling this feature on a port connected to a switch or hub could prevent spanning tree from detecting and disabling loops in your network, which could cause broadcast storms and address-learning problems.

To enable Port Fast on a non-trunked port, use the interface mode bridge port-fast enable command. You cannot configure Port Fast on a trunked port. By default, Port Fast is disabled on the port.

(config-if[2/1])#bridge port-fast enable

To disable the Port Fast feature, use the interface mode bridge port-fast disable command.

(config-if[2/1])#bridge port-fast disable

Enabling BPDU Guard

Use the BPDU guard feature to prevent a Port Fast port on the CSS from participating in the spanning tree. When you globally enable BPDU guard on the Port Fast ports, spanning tree shuts down the ports that receive BPDUs. For information to enable Port Fast on an interface port, see the “Configuring Port Fast on an Interface” section.

In a valid configuration, the enabled Port Fast ports do not receive BPDUs. Receiving a BPDU on a Port Fast-enabled port signals an invalid configuration, such as the connection of an unauthorized device, and the BPDU guard feature puts the port in the disabled state. The BPDU guard feature provides a secure response to invalid configurations because you must manually put the port back in service.

To enable the BPDU guard on the CSS, use the global configuration bridge bdpu-guard enabled command:

(config)# bridge bpdu-guard enabled

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