Spanning-Tree Backbonefast - Cisco Catalyst 3550 Command Reference Manual
Multilayer switch
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Chapter 2 Catalyst 3550 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 this 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(4)EA1
Usage Guidelines
You can configure 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 is started when a root port or blocked port on a switch receives inferior bridge protocol
data units (BPDUs) from its designated bridge. An inferior BPDU identifies one switch as both the root
bridge and the designated bridge. 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 bridge 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 ports 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
OL-8566-01
spanning-tree backbonefast
no spanning-tree backbonefast
Modification
This command was introduced.
summary Displays a summary of the spanning-tree port states.
Description
Catalyst 3550 Multilayer Switch Command Reference
spanning-tree backbonefast
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