Cisco WS-C3560E-48PD-SF Command Reference - Page 630
spanning-tree portfast
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spanning-tree portfast (global configuration) Chapter 2 Catalyst 3560 Switch Cisco IOS Commands 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 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 spanning-tree bpduguard spanning-tree portfast (interface configuration) Description Displays the current operating configuration. For syntax information, select Cisco IOS Configuration Fundamentals Command Reference, Release 12.2 > File Management Commands > Configuration File Management Commands. Prevents an interface from sending or receiving BPDUs. Puts an interface in the error-disabled state when it receives a BPDU. Enables the Port Fast feature on an interface in all its associated VLANs. 2-598 Catalyst 3560 Switch Command Reference 78-16405-05