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Chapter 2 Catalyst 3560 Switch Cisco IOS Commands
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.
Syntax Description
This command has no arguments or keywords.
Defaults
BackboneFast is disabled.
Command Modes
Global configuration
Command History
Release
12.1(19)EA1
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
show spanning-tree
78-16405-05
spanning-tree backbonefast
no spanning-tree backbonefast
Modification
This command was introduced.
summary Displays a summary of the spanning-tree interface states.
Description
Catalyst 3560 Switch Command Reference
spanning-tree backbonefast
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