Cisco Catalyst 3550

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Catalyst 3550 Multilayer Switch Command Reference
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Chapter 2 Catalyst 3550 Switch Cisco IOS Commands
spanning-tree portfast (global configuration)
Caution Enabling BPDU filtering on an interface is the same as disabling spanning tree on it and can result in
spanning-tree loops.
Use the spanning-tree portfast bpduguard default global configuration command to globally enable
BPDU guard on ports that are in a Port Fast-operational state. In a valid configuration, Port Fast-enabled
ports do not receive BPDUs. Receiving a BPDU on a Port Fast-enabled port signals an invalid
configuration, such as the connection of an unauthorized 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 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 ports. Configure Port Fast only on ports 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 port 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 ports 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 ports:
Switch(config)# spanning-tree portfast default
You can verify your settings by entering the show running-config privileged EXEC command.
Related Commands Command Description
show running-config Displays the current operating configuration. For syntax
information, select Cisco IOS Release 12.2 Configuration Guides
and Command References > Cisco IOS Configuration
Fundamentals Command Reference, Release 12.2 > File
Management Commands > Configuration File Management
Commands.
spanning-tree bpdufilter Prevents a port from sending or receiving BPDUs.
spanning-tree bpduguard Puts a port in the error-disabled state when it receives a BPDU.
spanning-tree portfast (interface
configuration)
Enables the Port Fast feature on an interface in all its associated
VLANs.