Cisco WS-C2960-24TC-S Software Guide - Page 536

Configuring Standard QoS Chapter 28 Configuring QoS Configuring the CoS Value for an Interface QoS assigns the CoS value specified with the mls qos cos interface configuration command to untagged frames received on trusted and untrusted ports. Beginning in privileged EXEC mode, follow these steps to define the default CoS value of a port or to assign the default CoS to all incoming packets on the port: Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Command configure terminal interface interface-id mls qos cos {default-cos | override} end show mls qos interface copy running-config startup-config Purpose Enter global configuration mode. Specify the port to be configured, and enter interface configuration mode. Valid interfaces include physical ports. Configure the default CoS value for the port. • For default-cos, specify a default CoS value to be assigned to a port. If the packet is untagged, the default CoS value becomes the packet CoS value. The CoS range is 0 to 7. The default is 0. • Use the override keyword to override the previously configured trust state of the incoming packet and to apply the default port CoS value to the port on all incoming packets. By default, CoS override is disabled. Use the override keyword when all incoming packets on specified ports deserve higher or lower priority than packets entering from other ports. Even if a port was previously set to trust DSCP, CoS, or IP precedence, this command overrides the previously configured trust state, and all the incoming CoS values are assigned the default CoS value configured with this command. If an incoming packet is tagged, the CoS value of the packet is modified with the default CoS of the port at the ingress port. Return to privileged EXEC mode. Verify your entries. (Optional) Save your entries in the configuration file. To return to the default setting, use the no mls qos cos {default-cos | override} interface configuration command. Configuring a Trusted Boundary to Ensure Port Security In a typical network, you connect a Cisco IP Phone to a switch port, as shown in Figure 28-11 on page 28-34, and cascade devices that generate data packets from the back of the telephone. The Cisco IP Phone guarantees the voice quality through a shared data link by marking the CoS level of the voice packets as high priority (CoS = 5) and by marking the data packets as low priority (CoS = 0). Traffic sent from the telephone to the switch is typically marked with a tag that uses the IEEE 802.1Q header. The header contains the VLAN information and the class of service (CoS) 3-bit field, which is the priority of the packet. For most Cisco IP Phone configurations, the traffic sent from the telephone to the switch should be trusted to ensure that voice traffic is properly prioritized over other types of traffic in the network. By using the mls qos trust cos interface configuration command, you configure the switch port to which 28-36 Catalyst 2960 Switch Software Configuration Guide OL-8603-04