Cisco Systems 3750E manual 13-25

Chapter 13 Configuring VLANs

Configuring VLAN Trunks

In this way, Trunk 1 carries traffic for VLANs 8 through 10, and Trunk 2 carries traffic for VLANs 3 through 6. If the active trunk fails, the trunk with the lower priority takes over and carries the traffic for all of the VLANs. No duplication of traffic occurs over any trunk port.

Figure 13-3 Load Sharing by Using STP Port Priorities

Switch A

Trunk 1

VLANs 8 – 10 (priority 16)

VLANs 3 – 6 (priority 128)

Switch B

Trunk 2

VLANs 3 – 6 (priority 16)

VLANs 8 – 10 (priority 128)

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Note If your switch is a member of a switch stack, you must use the spanning-tree[vlan vlan-id] cost cost interface configuration command instead of the spanning-tree[vlan vlan-id] port-prioritypriority interface configuration command to select an interface to put in the forwarding state. Assign lower cost values to interfaces that you want selected first and higher cost values that you want selected last. For more information, see the “Load Sharing Using STP Path Cost” section on page 13-26.

Beginning in privileged EXEC mode, follow these steps to configure the network shown in Figure 13-3.

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode on Switch A.
Step 2
	vtp domain domain-name	Configure a VTP administrative domain.
		The domain name can be 1 to 32 characters.
Step 3
	vtp mode server	Configure Switch A as the VTP server.
Step 4
	end	Return to privileged EXEC mode.
Step 5
	show vtp status	Verify the VTP configuration on both Switch A and Switch B.
		In the display, check the VTP Operating Mode and the VTP Domain
		Name fields.
Step 6
	show vlan	Verify that the VLANs exist in the database on Switch A.
Step 7
	configure terminal	Enter global configuration mode.
Step 8
	interface gigabitethernet1/ 0/1	Define the interface to be configured as a trunk, and enter interface
		configuration mode.
Step 9
	switchport trunk encapsulation {isl	Configure the port to support ISL or IEEE 802.1Q encapsulation or to
	dot1q negotiate}	negotiate with the neighboring interface. You must configure each end
		of the link with the same encapsulation type.
Step 10
	switchport mode trunk	Configure the port as a trunk port.
Step 11
	end	Return to privileged EXEC mode.
Step 12
	show interfaces gigabitethernet1/ 0/1	Verify the VLAN configuration.
	switchport
		Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02			13-25