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Catalyst 3750 Metro Switch Software Configuration Guide
78-15870-01
Chapter 16 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
Enabling BPDU Guard
When you globally enable BPDU guard on interfaces that are Port Fast-enabled (the interfaces are in a
Port Fast-operational state), spanning tree shuts down Port Fast-enabled interfaces that receive BPDUs.
In a valid configuration, Port Fast-enabled interfaces do not receive BPDUs. Receiving a BPDU on a
Port Fast-enabled interface signals an invalid configuration, such as the connection of an unauthorized
device, and the BPDU guard feature puts the interface in the error-disabled state. The BPDU guard
feature provides a secure response to invalid configurations because you must manually put the interface
back in service. Use the BPDU guard feature in a service-provider network to prevent an access port
from participating in the spanning tree.
Caution Configure Port Fast only on interfaces that connect to end stations; otherwise, an accidental topology
loop could cause a data packet loop and disrupt switch and network operation.
You also can use the spanning-tree bpduguard enable interface configuration command to enable
BPDU guard on any interface without also enabling the Port Fast feature. When the interface receives a
BPDU, it is put in the error-disabled state.
You can enable the BPDU guard feature if your switch is running PVST+, rapid PVST+, or MSTP.
Beginning in privileged EXEC mode, follow these steps to globally enable the BPDU guard feature. This
procedure is optional.
To disable BPDU guard, use the no spanning-tree portfast bpduguard default global configuration
command.
You can override the setting of the no spanning-tree portfast bpduguard default global configuration
command by using the spanning-tree bpduguard enable interface configuration command.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
spanning-tree portfast bpduguard default Globally enable BPDU guard.
By default, BPDU guard is disabled.
Step 3
interface interface-id Specify the interface connected to an end station, and enter
interface configuration mode.
Step 4
spanning-tree portfast Enable the Port Fast feature.
Step 5
end Return to privileged EXEC mode.
Step 6
show running-config Verify your entries.
Step 7
copy running-config startup-config (Optional) Save your entries in the configuration file.
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