Cisco Catalyst 3120 Command Reference Manual page 686

spanning-tree portfast (global configuration)
Enabling BPDU filtering on an interface is the same as disabling spanning tree on it and can result in
Caution
spanning-tree loops.
Use the spanning-tree portfast bpduguard default global configuration command to globally enable
BPDU guard on interfaces that are in a Port Fast-operational state. 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.
You can override the spanning-tree portfast bpduguard default global configuration command by
using the spanning-tree bdpuguard interface configuration command.
Use the spanning-tree portfast default global configuration command to globally enable the Port Fast
feature on all nontrunking interfaces. 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. A Port Fast-enabled interface moves directly to the spanning-tree forwarding state when
linkup occurs without waiting for the standard forward-delay time.
You can override the spanning-tree portfast default global configuration command by using the
spanning-tree portfast interface configuration command. You can use the no spanning-tree portfast
default global configuration command to disable Port Fast on all interfaces unless they are individually
configured with the spanning-tree portfast interface configuration command.
Examples
This example shows how to globally enable the BPDU filtering feature:
Switch(config)# spanning-tree portfast bpdufilter default
This example shows how to globally enable the BPDU guard feature:
Switch(config)# spanning-tree portfast bpduguard default
This example shows how to globally enable the Port Fast feature on all nontrunking interfaces:
Switch(config)# spanning-tree portfast default
You can verify your settings by entering the show running-config privileged EXEC command.
Related Commands Command
show running-config
spanning-tree bpdufilter
Cisco Catalyst Blade Switch 3120 for HP Command Reference
2-658
Chapter 2 Cisco Catalyst Blade Switch 3120 for HP Cisco IOS Commands
Description
Displays the operating configuration. For syntax information, use
this link to the Cisco IOS Release 12.2 Command Reference
listing page:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/prod
_command_reference_list.html
Select the Cisco IOS Commands Master List, Release 12.2 to
navigate to the command.
Prevents an interface from sending or receiving BPDUs.
OL-12248-01