Cisco Catalyst 2960-X Command Reference Manual page 113

Layer 2 Commands
spanning-tree portfast (global configuration)
Be careful when using this command. Enabling BPDU filtering on an interface is the same as disabling
Caution
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 interfaces that are in a PortFast-operational state. In a valid configuration, PortFast-enabled interfaces
do not receive BPDUs. Receiving a BPDU on a PortFast-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 command by using the spanning-tree
portfast bpduguard interface command.
Use the spanning-tree portfast default command to globally enable the PortFast feature on all nontrunking
interfaces. Configure PortFast 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 PortFast-enabled interface
moves directly to the spanning-tree forwarding state when linkup occurs; it does not wait 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 PortFast 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 by default:
Switch(config)# spanning-tree portfast bpdufilter default
This example shows how to globally enable the BDPU guard feature by default:
Switch(config)# spanning-tree portfast bpduguard default
This example shows how to globally enable the PortFast feature on all nontrunking interfaces:
Switch(config)# spanning-tree portfast default
Catalyst 2960-X Switch Layer 2 Command Reference, Cisco IOS Release 15.0(2)EX
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