Cisco 2950 Software Configuration Guide - Page 600

Standard QoS Configuration Examples Chapter 30 Configuring QoS Figure 30-5 QoS Configuration Example Network Cisco router To Internet Existing wiring closet Trunk link Trunk link Gigabit Ethernet 0/2 Intelligent wiring closet Video server 172.20.10.16 Gigabit Ethernet 0/1 111387 End stations QoS Configuration for the Existing Wiring Closet Figure 30-5 shows an existing wiring closet with Catalyst 2900 XL and 3500 XL switches, for example. These switches are running Cisco IOS Release 12.0(5)XP or later, which supports the QoS-based IEEE 802.1p CoS values. QoS classifies frames by assigning priority-indexed CoS values to them and gives preference to higher-priority traffic. Recall that on the Catalyst 2900 and 3500 XL switches, you can classify untagged (native) Ethernet frames at the ingress ports by setting a default CoS priority (switchport priority default default-priority-id interface configuration command) for each port. For IEEE 802.1Q frames with tag information, the priority value from the header frame is used. On the Catalyst 3524-PWR XL and 3548 XL switches, you can override this priority with the default value by using the switchport priority default override interface configuration command. For Catalyst 2950 and Catalyst 2900 XL switches and other 3500 XL models that do not have the override feature, the Catalyst 3550-12T switch at the distribution layer can override the 802.1p CoS value by using the mls qos cos override interface configuration command. 30-40 Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 78-11380-10