Specifications

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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 14 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
These sections describe how to configure optional spanning-tree features:
• Default Optional Spanning-Tree Configuration, page 14-14
• Enabling Port Fast, page 14-14
• Enabling BPDU Guard, page 14-15
• Enabling BPDU Filtering, page 14-16
• Enabling UplinkFast for Use with Redundant Links, page 14-17
• Enabling Cross-Stack UplinkFast, page 14-18
• Enabling BackboneFast, page 14-19
• Enabling EtherChannel Guard, page 14-19
• Enabling Root Guard, page 14-20
• Enabling Loop Guard, page 14-20
Default Optional Spanning-Tree Configuration
Table 14-1 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 17,
“Configuring Voice VLAN.”
Table 14-1 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.
EtherChannel guard Globally enabled.
Root guard Disabled on all interfaces.
Loop guard Disabled on all interfaces.