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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 13 Configuring Optional Spanning-Tree Fea tures Configuring Optional Spanning-Tree Features

Enabling BackboneFast

You can en able Bac kbone Fast to detect in direc t link failures and to start the spanning- tree
reconfigur atio n soo ne r.
Note If yo u use Bac kbon eFast, you m ust e nable it o n all swi tch es i n th e network. B ackb oneFast is no t
supported on Token Ring VL ANs. Thi s fea tur e is su ppor ted f or use w it h th ird- part y swit che s.
The Back boneFast fe ature is supp orted only w hen the sw itch is runnin g PVST.
Beginning in privileged EXEC mode, follow these steps to enable BackboneFast:
To disable the BackboneFast feature, use the no spanning-tree backbo nefast global configur ation
command.

Enabling Root Guard

Root guar d enable d on an inte rface appli es to all the V LANs to which the i nterface be longs.
Do not enable the root guard on interfaces to be used by the UplinkFast feature. With UplinkFast, the
backup i nterfaces (i n the blocked state) replace th e 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-i nconsist ent stat e (blocke d) and ar e prevented from reac hing the forwardin g state.
Note Yo u canno t ena ble bo th r oot gua rd and l oop gu ar d a t th e sam e time .
You can enable this feature if your switch is running PVST or MSTP. The MSTP is av ailable only if you
have the EI installe d on your switc h.
Beginning i n privileged EX EC mode , foll ow these s te ps t o ena ble r oot guard on a n inter face:
Command Purpose
Step 1 configure terminal Enter glo bal co nfigur ati on mo de.
Step 2 spanning-tree backbonefast Enab le Backbone Fast.
Step 3 end Return to privileged EXEC mode.
Step 4 show spanning-tree summary Verify your entries.
Step 5 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Step 1 configure terminal Enter glob al con figuration mo de.
Step 2 interface interface-id Enter interface configuration mode, and specify an interface to configure.
Step 3 spanning-tree guard root Enable r oot gua rd on the inter face.
By default, root guard is disabled on all interfaces.
Step 4 end Return to privileged EXEC mode.