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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 16 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
• Enabling BackboneFast, page 16-18 (optional)
• Enabling EtherChannel Guard, page 16-18 (optional)
• Enabling Root Guard, page 16-19 (optional)
• Enabling Loop Guard, page 16-19 (optional)
Default Optional Spanning-Tree Configuration
Table 16-1 shows the default optional spanning-tree configuration.
Optional Spanning-Tree Configuration Guidelines
You can configure PortFast, BPDU guard, BPDU filtering, EtherChannel guard, root guard, or loop
guard if your switch is running PVST+, rapid PVST+, or MSTP.
You can configure the UplinkFast, the BackboneFast, or the cross-stack UplinkFast feature for rapid
PVST+ or for the MSTP, but the feature remains disabled (inactive) until you change the spanning-tree
mode to PVST+.
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 19,
“Configuring Voice VLAN.”
You can enable this feature if your switch is running PVST+, rapid PVST+, or MSTP.
Table 16-1 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.
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