spanning-tree portfast

Enables the Port Fast feature on an interface to allow the interface to quickly transition to forwarding state.

Syntax

spanning-tree portfast [ bpdu-guard ]
no spanning-tree portfast [ bpdu-guard ]

Command Default

Port Fast is disabled.

Parameters

bpdu-guard
Guards the port against the reception of BPDUs.

Modes

Interface subtype configuration mode

Usage Guidelines

This command is applicable the only for the Spanning Tree Protocol (STP). Port Fast immediately puts the interface into the forwarding state without having to wait for the standard forward time. Use the spanning-tree edgeport command for MSTP and RSTP.

BPDU guard disables all portfast-enabled ports should they ever receive BPDU frames. It does not prevent transmitting of BPDU frames.

If you enable spanning-tree portfast bpdu-guard on an interface and the interface receives a BPDU, the software disables the interface and puts the interface in the ERR_DISABLE state.

Enable Port Fast on ports connected to host. Enabling Port Fast on interfaces connected to switches, bridges, hubs, and so on can cause temporary bridging loops, in both trunking and nontrunking mode.

Examples

To enable a port to quickly transition to the forwarding state:

device# configure terminal
device(config)# interface ethernet 1/5 
device(conf-if-eth-1/5)# spanning-tree portfast 

To guard the port against reception of BPDUs:

device# configure terminal
device(config)# interface ethernet 1/5 
device(conf-if-eth-1/5)# spanning-tree portfast 
device(conf-if-eth-1/5)# spanning-tree portfast bpdu-guard