Cisco Catalyst 3750 Metro

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Catalyst 3750 Metro Switch Command Reference
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Chapter 2 Catalyst 3750 Metro Switch Cisco IOS Commands
spanning-tree portfast (global configuration)
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.
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. When Port Fast is enabled, the interface changes directly from a
blocking state to a forwarding state without making the intermediate spanning-tree state changes.
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 BPDU filtering:
Switch(config)# spanning-tree portfast bpdufilter default
This example shows how to globally enable BPDU guard:
Switch(config)# spanning-tree portfast bpduguard default
This example shows how to globally enable Port Fast 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 Description
show running-config 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.
spanning-tree bpdufilter Prevents an interface from sending or receiving BPDUs.
spanning-tree bpduguard Puts an interface 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.