Cisco WS-C2950T-24 Software Guide - Page 254

Load Sharing Using STP Chapter 8 Configuring VLANs Configuring the CoS Port Priorities Beginning in privileged EXEC mode, follow these steps to set the port priority for untagged (native) Ethernet frames: Step 1 Step 2 Step 3 Command configure terminal interface interface switchport priority default default-priority-id Step 4 Step 5 end show interface interface-id switchport Purpose Enter global configuration mode. Enter the interface to be configured. Set the port priority on the interface. If you assign a priority level from 0 to 3, frames are forwarded to the normal priority queue of the output port. If you assign a priority level from 4 to 7, frames are forwarded to the high-priority queue of the output port. Return to privileged EXEC mode. Verify your entries. In the display, check the Priority for Untagged Frames field. 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. With 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 the "Configuring STP" section on page 6-33. 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 standby mode. 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 8-5 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. 8-32 Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide 78-6511-08