Cisco WS-C2960-24PC-L Software Guide - Page 243
Load-Sharing VLAN Traffic over Parallel Trunks Example
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Chapter 11 Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports Example VLAN Trunk Configurations 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 shows a parallel trunk configuration between two switches, using the Fast Ethernet uplink ports on the supervisor engine. Figure 11-2 Parallel Trunk Configuration Before Configuring VLAN-Traffic Load Sharing Trunk 2 VLANs 10, 20, and 30: port-VLAN priority 32 (blocking) VLANs 40, 50, and 60: port-VLAN priority 1 (forwarding) Catalyst 4000 Switch 1 Catalyst 4000 Switch 2 1/1 1/2 1/1 1/2 43991 Trunk 1 VLANs 10, 20, and 30: port-VLAN priority 1 (forwarding) VLANs 40, 50, and 60: port-VLAN priority 32 (blocking) By default, the port-VLAN priority for both trunks is equal (a value of 32). Therefore, 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: Step 1 Step 2 Configure a VTP domain on both Switch 1 and Switch 2 by entering the set vtp command so that the VLAN information 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) 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 Vlan 30 configuration successful Switch_1> (enable) set vlan 40 78-15486-01 Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide-Release 8.1 11-13
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