Load-Sharing Vlan Traffic Over Parallel Trunks Example - Cisco WS-C2948G-GE-TX Configuration Manual

Chapter 11 Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports

Load-Sharing VLAN Traffic over Parallel Trunks Example

Using spanning tree port-VLAN priorities, you can load-share VLAN traffic over parallel trunk ports so
that traffic from some VLANs travels over one trunk, while traffic from other VLANs travels over the
other trunk. This configuration allows traffic to be carried over both trunks simultaneously (instead of
keeping one trunk in blocking mode), which reduces the total traffic carried over each trunk while still
maintaining a fault-tolerant configuration.
Figure 11-2
ports on the supervisor engine.
Figure 11-2 Parallel Trunk Configuration Before Configuring VLAN-Traffic Load Sharing
1/1
By default, the port-VLAN priority for both trunks is equal (a value of 32). STP blocks port 1/2
(Trunk 2) for each VLAN on Switch 1 to prevent forwarding loops. Trunk 2 is not used to forward traffic
unless Trunk 1 fails.
To configure the switches so that traffic from multiple VLANs is load balanced over the parallel trunks,
follow these steps:
Configure a VTP domain on both Switch 1 and Switch 2 by entering the set vtp command so that the
Step 1
VLAN information that is configured on Switch 1 is learned by Switch 2. Make sure that Switch 1 is a
VTP server. You can configure Switch 2 as a VTP client or as a VTP server.
Switch_1> (enable) set vtp domain BigCorp mode server
VTP domain BigCorp modified
Switch_1> (enable)
Switch_2> (enable) set vtp domain BigCorp mode server
VTP domain BigCorp modified
Switch_2> (enable)
Step 2 Create the VLANs on Switch 1 by entering the set vlan command. In this example, you see VLANs 10,
20, 30, 40, 50, and 60.
Switch_1> (enable) set vlan 10
Vlan 10 configuration successful
Switch_1> (enable) set vlan 20
Vlan 20 configuration successful
Switch_1> (enable) set vlan 30
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
78-15908-01
shows a parallel trunk configuration between two switches, using the Fast Ethernet uplink
Trunk 2
VLANs 10, 20, and 30: port-VLAN priority 32 (blocking)
VLANs 40, 50, and 60: port-VLAN priority 1 (forwarding)
Catalyst 4500
Switch 1
1/2
Trunk 1
VLANs 10, 20, and 30: port-VLAN priority 1 (forwarding)
VLANs 40, 50, and 60: port-VLAN priority 32 (blocking)
Example VLAN Trunk Configurations
Catalyst 4500
Switch 2
1/1
1/2
11-13