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Catalyst2950 Desktop Switch Software Configuration Guide
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Chapter12 Configuring Optiona l Spa nning-Tree Features Configuring Optional Spanning-Tree Features
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.
You can also use the spanning-tree bpduguard enable interface configuration command to enable
BPDU guard on any port without also enabling the Port Fast fe atu r e. When th e po r t re ce ives a BPDU, it
is put in the error-disabled state.
You can enable the BPDU guard feature if your switch is running PVST or MSTP. The MSTP is available
only if you have the EI installed on your switch.
Beginning in privileged EXEC mode, follow these steps to globally enable the BPDU guard feature:
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.
Command Purpose
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 spanning-tree portfast bpduguard default Globally enable BPDU guard.
By default, BPDU guard is disabled.
Step3 interface interface-id Enter interface configuration mode, and specify the interface
connected to an end station.
Step4 spanning-tree portfast Enable the Port Fast feature.
Step5 end Return to privileged EXEC mode.