Cisco Systems 3750E Default Spanning-Tree Configuration, Spanning-Tree Configuration Guidelines

Chapter 18 Configuring STP

Configuring Spanning-Tree Features

•Configuring the Switch Priority of a VLAN, page 18-21(optional)

•Configuring Spanning-Tree Timers, page 18-22(optional)

Default Spanning-Tree Configuration

Table 18-3shows the default spanning-tree configuration.

Table 18-3	Default Spanning-Tree Configuration
Feature		Default Setting
Enable state		Enabled on VLAN 1.
		For more information, see the “Supported
		Spanning-Tree Instances” section on
		page 18-10.
Spanning-tree mode		PVST+. (Rapid PVST+ and MSTP are
		disabled.)
Switch priority		32768.
Spanning-tree port priority (configurable on a per-interface basis)		128.
Spanning-tree port cost (configurable on a per-interface basis)		1000 Mb/s: 4.
		100 Mb/s: 19.
		10 Mb/s: 100.
Spanning-tree VLAN port priority (configurable on a per-VLAN basis)		128.
Spanning-tree VLAN port cost (configurable on a per-VLAN basis)		1000 Mb/s: 4.
		100 Mb/s: 19.
		10 Mb/s: 100.
Spanning-tree timers		Hello time: 2 seconds.
		Forward-delay time: 15 seconds.
		Maximum-aging time: 20 seconds.
		Transmit hold count: 6 BPDUs

Spanning-Tree Configuration Guidelines

Each stack member runs its own spanning tree, and the entire stack appears as a single switch to the rest of the network.

If more VLANs are defined in the VTP than there are spanning-tree instances, you can enable PVST+ or rapid PVST+ on only 128 VLANs on the switch or each switch stack. The remaining VLANs operate with spanning tree disabled. However, you can map multiple VLANs to the same spanning-tree instances by using MSTP. For more information, see Chapter 19, “Configuring MSTP.”

If 128 instances of spanning tree are already in use, you can disable spanning tree on one of the VLANs and then enable it on the VLAN where you want it to run. Use the no spanning-tree vlan vlan-idglobal configuration command to disable spanning tree on a specific VLAN, and use the spanning-tree vlan vlan-idglobal configuration command to enable spanning tree on the desired VLAN.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02		18-13