Cisco 2950 Software Configuration Guide - Page 571

Chapter 30 Configuring QoS Configuring Auto-QoS When you enable the auto-QoS feature on the first interface, these automatic actions occur: • When you enter the auto qos voip cisco-phone interface configuration command on a port at the edge of a network that is connected to a Cisco IP Phone, the switch enables the trusted boundary feature. The switch uses the Cisco Discovery Protocol (CDP) to detect the presence or absence of a Cisco IP Phone. When a Cisco IP Phone is detected, the ingress classification on the interface is set to trust the QoS label received in the packet. When a Cisco IP Phone is absent, the ingress classification is set to not trust the QoS label in the packet. The switch configures egress queues on the port according to the settings in Table 30-3. • When you enter the auto qos voip cisco-softphone interface configuration command on a port at the edge of the network that is connected to a device running the Cisco SoftPhone, the switch uses policing to decide whether a packet is in or out of profile and to specify the action on the packet. If the packet does not have a DSCP value of 24, 26, or 46 or is out of profile, the switch changes the DSCP value to 0. The switch configures egress queues on the port according to the settings in Table 30-3. • When you enter the auto qos voip trust interface configuration command on a port connected to the interior of the network, the switch trusts the CoS value in ingress packets (the assumption is that traffic has already been classified by other edge devices). The switch configures egress queues on the port according to the settings in Table 30-3. For information about the trusted boundary feature, see the "Configuring Trusted Boundary" section on page 30-23. When you enable auto-QoS by using the auto qos voip cisco-phone, the auto qos voip cisco-softphone, or the auto qos voip trust interface configuration command, the switch automatically generates a QoS configuration based on the traffic type and ingress packet label and applies the commands listed in Table 30-4 to the interface. Table 30-4 Generated Auto-QoS Configuration Description Automatically Generated QoS Command Equivalent The switch automatically enables standard QoS and configures Switch(config)# mls qos map cos-dscp 0 8 16 26 32 46 the CoS-to-DSCP map (maps CoS values in incoming packets 48 56 to a DSCP value) as shown in Table 30-2 on page 30-10. If you entered the auto qos voip trust command, the switch Switch(config-if)# mls qos trust cos automatically sets the ingress classification on the interface to trust the CoS value received in the packet. If you entered the auto qos voip cisco-phone command, the switch automatically enables the trusted boundary feature, which uses the CDP to detect the presence or absence of a Cisco IP Phone. Switch(config-if)# mls qos trust device cisco-phone 78-11380-10 Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 30-11