Cisco 2950G 24 Software Configuration Guide - Page 357

Chapter 14 Configuring VLANs Configuring VLAN Trunks Beginning in privileged EXEC mode, follow these steps to configure the native VLAN on an 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. Enter interface configuration mode, and define the interface that is configured as the 802.1Q trunk. Configure the VLAN that is sending and receiving untagged traffic on the trunk port. For vlan-id, the range is 1 to 4094 when the EI is installed, and 1 to 1005 when the SI is installed. Do not enter leading zeros. 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. Load Sharing Using STP 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 11, "Configuring STP." Load Sharing Using STP Port Priorities When two ports on the same switch form a loop, the STP port priority setting determines 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 14-3 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 10 on Trunk 1. • VLANs 3 through 6 retain the default port priority of 128 on Trunk 1. • VLANs 3 through 6 are assigned a port priority of 10 on Trunk 2. • VLANs 8 through 10 retain the default port priority of 128 on Trunk 2. 78-14982-01 Catalyst 2950 Desktop Switch Software Configuration Guide 14-21