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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 13 Configuring Optional Spanning-Tree Features
Configur ing Optiona l Spanning-Tree Features

Default Optional Spanning-Tree Conf iguration

Table 13-1 shows th e de fault o pt iona l span ni ng-tr ee co nfigurati on.

Enabling Port Fast

A port with the Po rt Fast feature enabled is mo ved directly to the spanning-tre e forwardi ng state without
waiting fo r the stan dard fo rward-t ime delay.
Caution Use Port Fa st only when connecting a single end station to an access or trunk port. Enabling this feature
on a po rt c on nect ed to a swi tch o r hub co uld prevent span ning tre e fr om det ect ing an d di sab ling l o ops
in your n etwork, whi ch c ou ld ca use broa dcast storm s and a ddress -l earn ing pro ble ms.
If yo u enab le the voice VL AN f eature, the Port F a s t f eature i s au tomatically en ab led . When y o u disable
v oic e VLA N , the Po rt Fast feature is not aut om ati cally disabled . For more inf o rmatio n , s ee Chapter 16,
Configuring Voice VLA N.
You can enable this feature if your switch is running PVST or MSTP. The MSTP is available only if you
have the EI installed on your sw itch.
Beginning in privileged EXEC mode, follow these steps to enable Port Fast:
Table 13-1 Default Optional Spanning-Tree Configuration
Feature Default Setting
Port Fast, BPDU filtering , BPDU guar d Globally di sabled (unless they are individual ly configured
per int e rface ).
Uplink Fast Globally di sabled .
CSUF Disabled on all interfaces.
Backb oneFast Globally di sabled .
Root gua rd Disabled o n all interfa ces.
Loop guard Disabled on all interfaces.
Command Purpose
Step 1 configure terminal Enter globa l configurati on mode.
Step 2 interface interface-id Enter interface configuration mode, and specify an interface to
configure.
Step 3 spanning-tree portfast [trunk] Enable Po rt Fast on a n acc ess por t c onnec ted to a si ng le
workstation or server . By specifying the trunk keyword, you can
enable Po rt Fast on a t r unk po rt .
Caution M ake sur e tha t t here are no l oops in the ne twork
betwee n the tru nk port and the workst atio n o r server
before you enab le Port Fast on a trunk port.
By default, Port Fast is disa bled on all po rts.