Cisco Systems 3750E manual Default Optional Spanning-Tree Configuration, Enabling Port Fast, 20-12

Chapter 20 Configuring Optional Spanning-Tree Features

Configuring Optional Spanning-Tree Features

•Enabling BackboneFast, page 20-16(optional)

•Enabling EtherChannel Guard, page 20-17(optional)

•Enabling Root Guard, page 20-18(optional)

•Enabling Loop Guard, page 20-18(optional)

Default Optional Spanning-Tree Configuration

Table 20-1shows the default optional spanning-tree configuration.

Table 20-1	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. (On Catalyst 3750-E switches, the
		UplinkFast feature is the CSUF feature.)
BackboneFast		Globally disabled.
EtherChannel guard		Globally enabled.
Root guard		Disabled on all interfaces.
Loop guard		Disabled on all interfaces.

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.

On a Catalyst 3750-E switch, 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+.

On a Catalyst 3560-E switch, you can configure the UplinkFast or the BackboneFast 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

An interface 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 an interface 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.”

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
20-12	OL-9775-02