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Catalyst 2950 Desktop Switch Software Configuration Guide
78-11380-05
Chapter 12 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
Default Optional Spanning-Tree Configuration
Table 12-1 shows the default optional spanning-tree configuration.
Enabling Port Fast
A port with the Port Fast feature enabled is moved directly to the spanning-tree forwarding state without
waiting for the standard forward-time delay.
Caution Use Port Fast only when connecting a single end station to an access or trunk port. Enabling this feature
on a port connected to a switch or hub could prevent spanning tree from detecting and disabling loops
in your network, which could cause broadcast storms and address-learning problems.
If you enable the voice VLAN feature, the Port Fast feature is automatically enabled. When you disable
voice VLAN, the Port Fast feature is not automatically disabled. For more information, see Chapter 15,
“Configuring Voice VLAN.”
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 switch.
Beginning in privileged EXEC mode, follow these steps to enable Port Fast:
Table 12-1 Default Optional Spanning-Tree Configuration
Feature Default Setting
Port Fast, BPDU filtering, BPDU guard Globally disabled (unless they are individually configured
per interface).
UplinkFast Globally disabled.
CSUF Disabled on all interfaces.
BackboneFast Globally disabled.
Root guard Disabled on all interfaces.
Loop guard Disabled on all interfaces.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Enter interface configuration mode, and specify an interface to
configure.
Step 3
spanning-tree portfast [trunk] Enable Port Fast on an access port connected to a single
workstation or server. By specifying the trunk keyword, you can
enable Port Fast on a trunk port.
Caution Make sure that there are no loops in the network
between the trunk port and the workstation or server
before you enable Port Fast on a trunk port.
By default, Port Fast is disabled on all ports.