Cisco WS-C3560V2-24TS-E Command Reference - Page 593
spanning-tree backbonefast, Catalyst 3560 Switch Command Reference,
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Chapter 2 Catalyst 3560 Switch Cisco IOS Commands spanning-tree backbonefast spanning-tree backbonefast Use the spanning-tree backbonefast global configuration command to enable the BackboneFast feature. Use the no form of the command to return to the default setting. spanning-tree backbonefast no spanning-tree backbonefast Syntax Description This command has no arguments or keywords. Defaults BackboneFast is disabled. Command Modes Global configuration Command History Release 12.1(19)EA1 Modification This command was introduced. Usage Guidelines You can configure the BackboneFast feature for rapid PVST+ or for multiple spanning-tree (MST) mode, but the feature remains disabled (inactive) until you change the spanning-tree mode to PVST+. BackboneFast starts when a root port or blocked port on a switch receives inferior BPDUs from its designated switch. An inferior BPDU identifies a switch that declares itself as both the root bridge and the designated switch. When a switch receives an inferior BPDU, it means that a link to which the switch is not directly connected (an indirect link) has failed (that is, the designated switch has lost its connection to the root switch. If there are alternate paths to the root switch, BackboneFast causes the maximum aging time on the interfaces on which it received the inferior BPDU to expire and allows a blocked port to move immediately to the listening state. BackboneFast then transitions the interface to the forwarding state. For more information, see the software configuration guide for this release. Enable BackboneFast on all supported switches to allow the detection of indirect link failures and to start the spanning-tree reconfiguration sooner. Examples This example shows how to enable BackboneFast on the switch: Switch(config)# spanning-tree backbonefast You can verify your setting by entering the show spanning-tree summary privileged EXEC command. Related Commands Command Description show spanning-tree summary Displays a summary of the spanning-tree interface states. 78-16405-05 Catalyst 3560 Switch Command Reference 2-561