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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
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Chapter16 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
Beginning in privileged EXEC mode, follow these steps to enable Port Fast. This procedure is optional.
Note You can use the spanning-tree portfast default global configuration command to globally enable the
Port Fast feature on all nontrunking ports.
To disable the Port Fast feature, use the spanning-tree portfast disable interface configuration
command.
Enabling BPDU Guard
When you globally enable BPDU guard on ports that are Port Fast-enabled (the ports are in a Port
Fast-operational state), spanning tree shuts down Port Fast-enabled ports that receive BPDUs.
In a valid configuration, Port Fast-enabled ports do not receive BPDUs. Receiving a BPD U on a Po rt
Fast-enabled port signals an invalid configuration, such as the connection of an unauthorize d device, and
the BPDU guard feature puts the port in the error-disabled state. The BPDU guard feature provides a
secure response to invalid configurations because you must manually put the port back in service. Use
the BPDU guard feature in a service-provider network to prevent an acce ss port fro m participatin g in the
spanning tree.
Caution Configure Port Fast only on ports that connect to end stations; othe rwi se, a n acci dent al topol ogy l oo p
could cause a data packet loop and disrupt switch and network operation.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Specify an interface to configure, and enter interface
configuration mode.
Step3 spanning-tree portfast [trunk] Enable Port Fast on an access port connected to a single
workstation or server. By specifying the trunk keyword, you can
enable Port Fast on a trunk port.
Note To enable Port Fast on trunk ports, you must use the
spanning-tree portfast trunk interface configuration
command. The spanning-tree portfast command will
not work on trunk ports.
Caution Make sure that there are no loops in the network
between the trunk port and the workstation or server
before you enable Port Fast on a trunk port.
By default, Port Fast is disabled on all ports.
Step4 end Return to privileged EXEC mode.
Step5 show spanning-tree interface interface-id
portfast Verify your entries.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.