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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter10 Configuring STP
Configuring Advanced STP Features
Configuring BackboneFast
You can enable BackboneFast to detect indirect link failures and to start the spanning-tree
reconfiguration sooner.
Note If you use BackboneFast, you must enable it on all switches in the ne tw ork. Bac kbone Fast is n ot
supported on Token Ring VLANs. This feature is supported for use with third-party switches.
Beginning in privileged EXEC mode, follow these steps to enable Ba ckbon eFa st:
To disable the BackboneFast feature, use the no spanning-tree backbonefast global configuration
command.
Configuring Root Guard
Root guard enabled on an interface applies to all the VLANs to which the interface belongs. Each VLAN
has its own spanning-tree instance.
Do not enable the root guard on interfaces to be used by the UplinkFast feature. With UplinkFast, the
backup interfaces (in the blocked state) replace the root port in the case of a failure. However, if root
guard is also enabled, all the backup interfaces used by the UplinkFast feature are placed in the
root-inconsistent state (blocked) and are prevente d fro m re achi ng the f or ward ing stat e .
Beginning in privileged EXEC mode, follow these steps to enable root guard on an interface:
To disable the root guard feature, use the no spanning-tree guard or the spanning-tree guard none
interface configuration command.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 spanning-tree backbonefast Enable BackboneFast on the switch.
Step3 end Return to privileged EXEC mode.
Step4 show spanning-tree vlan vlan-id Verify your entries.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Enter interface configuration mode, and specify an interface to
configure. Valid interfaces include physical interfaces and
port-channel logical interfaces (port-channel port-channel-number).
Step3 spanning-tree guard root Enable root guard on the interface.
By default, root guard is disabled on all interfaces.
Step4 end Return to privileged EXEC mode.
Step5 show running-config Verify your entries.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.