Cisco WS-C2960-24TC-S Software Guide - Page 270
Configuring Trunk Ports for Load Sharing, Load Sharing Using STP Port Priorities
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Configuring VLAN Trunks Chapter 12 Configuring VLANs For information about IEEE 802.1Q configuration issues, see the "IEEE 802.1Q Configuration Considerations" section on page 12-15. Beginning in privileged EXEC mode, follow these steps to configure the native VLAN on an IEEE 802.1Q trunk: Step 1 Step 2 Command configure terminal interface interface-id Step 3 switchport trunk native vlan vlan-id Step 4 Step 5 Step 6 end show interfaces interface-id switchport copy running-config startup-config Purpose Enter global configuration mode. Define the interface that is configured as the IEEE 802.1Q trunk, and enter interface configuration mode. Configure the VLAN that is sending and receiving untagged traffic on the trunk port. For vlan-id, the range is 1 to 4094. Return to privileged EXEC mode. Verify your entries in the Trunking Native Mode VLAN field. (Optional) Save your entries in the configuration file. To return to the default native VLAN, VLAN 1, use the no switchport trunk native vlan interface configuration command. If a packet has a VLAN ID that is the same as the outgoing port native VLAN ID, the packet is sent untagged; otherwise, the switch sends the packet with a tag. Configuring Trunk Ports for Load Sharing Load sharing divides the bandwidth supplied by parallel trunks connecting switches. To avoid loops, STP normally blocks all but one parallel link between switches. Using load sharing, you divide the traffic between the links according to which VLAN the traffic belongs. You configure load sharing on trunk ports by using STP port priorities or STP path costs. For load sharing using STP port priorities, both load-sharing links must be connected to the same switch. For load sharing using STP path costs, each load-sharing link can be connected to the same switch or to two different switches. For more information about STP, see Chapter 15, "Configuring STP." Load Sharing Using STP Port Priorities When two ports on the same switch form a loop, the switch uses the STP port priority to decide which port is enabled and which port is in a blocking state. You can set the priorities on a parallel trunk port so that the port carries all the traffic for a given VLAN. The trunk port with the higher priority (lower values) for a VLAN is forwarding traffic for that VLAN. The trunk port with the lower priority (higher values) for the same VLAN remains in a blocking state for that VLAN. One trunk port sends or receives all traffic for the VLAN. Figure 12-2 shows two trunks connecting supported switches. In this example, the switches are configured as follows: • VLANs 8 through 10 are assigned a port priority of 16 on Trunk 1. • VLANs 3 through 6 retain the default port priority of 128 on Trunk 1. 12-20 Catalyst 2960 Switch Software Configuration Guide OL-8603-04
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