Cisco Systems 3750E Configuring Path Cost, Port-channel-number, Spanning-tree cost cost, 18-20

Chapter 18 Configuring STP

Configuring Spanning-Tree Features

To return to the default setting, use the no spanning-tree[vlan vlan-id] port-priorityinterface configuration command. For information on how to configure load sharing on trunk ports by using spanning-tree port priorities, see the “Configuring Trunk Ports for Load Sharing” section on page 13-24.

Configuring Path Cost

The spanning-tree path cost default value is derived from the media speed of an interface. If a loop occurs, spanning tree uses cost when selecting an interface to put in the forwarding state. You can assign lower cost values to interfaces that you want selected first and higher cost values that you want selected last. If all interfaces have the same cost value, spanning tree puts the interface with the lowest interface number in the forwarding state and blocks the other interfaces.

Beginning in privileged EXEC mode, follow these steps to configure the cost of an interface. This procedure is optional.

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	interface interface-id	Specify an interface to configure, and enter interface
		configuration mode. Valid interfaces include physical ports and
		port-channel logical interfaces (port-channel
		port-channel-number).
Step 3
	spanning-tree cost cost	Configure the cost for an interface.
		If a loop occurs, spanning tree uses the path cost when selecting
		an interface to place into the forwarding state. A lower path cost
		represents higher-speed transmission.
		For cost, the range is 1 to 200000000; the default value is derived
		from the media speed of the interface.
Step 4
	spanning-tree vlan vlan-idcost cost	Configure the cost for a VLAN.
		If a loop occurs, spanning tree uses the path cost when selecting
		an interface to place into the forwarding state. A lower path cost
		represents higher-speed transmission.
		• For vlan-id, you can specify a single VLAN identified by
		VLAN ID number, a range of VLANs separated by a hyphen,
		or a series of VLANs separated by a comma. The range is 1
		to 4094.
		• For cost, the range is 1 to 200000000; the default value is
		derived from the media speed of the interface.
Step 5
	end	Return to privileged EXEC mode.
Step 6
	show spanning-tree interface interface-id	Verify your entries.
	or
	show spanning-tree vlan vlan-id
Step 7
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
18-20	OL-9775-02