Cisco 2950G 24 Software Configuration Guide - Page 532

Configuring QoS Chapter 26 Configuring QoS However, if a user bypasses the telephone and connects the PC directly to the switch, the CoS labels generated by the PC are trusted by the switch (because of the trusted CoS setting) and can allow misuse of high-priority queues. The trusted boundary feature solves this problem by using the Cisco Discovery Protocol (CDP) to detect the presence of a Cisco IP phone (such as the Cisco IP Phone 7910, 7935, 7940, and 7960) on a switch port. If the telephone is not detected, the trusted boundary feature disables the trusted setting on the switch port and prevents misuse of a high-priority queue. Beginning in privileged EXEC mode, follow these steps to configure trusted boundary on a switch port: Step 1 Step 2 Step 3 Command configure terminal cdp enable interface interface-id Step 4 Step 5 Step 6 cdp enable mls qos trust device cisco-phone mls qos trust cos Step 7 Step 8 Step 9 end show mls qos interface [interface-id] [policers] copy running-config startup-config Purpose Enter global configuration mode. Enable CDP globally. By default, it is enabled. Enter interface configuration mode, and specify the interface to be trusted. Valid interfaces include physical interfaces. Enable CDP on the interface. By default, CDP is enabled. Configure the Cisco IP phone as a trusted device on the interface. Configure the port trust state to trust the CoS value of the ingress packet. By default, the port is not trusted. Note In software releases earlier than Release 12.1(11)EA1, the mls qos trust cos command is available only when the switch is running the EI. For more information on this command, refer to the command reference for this release. Return to privileged EXEC mode. Verify your entries. (Optional) Save your entries in the configuration file. When you enter the no mls qos trust interface configuration command, trusted boundary is not disabled. If this command is entered and the port is connected to a Cisco IP phone, the port does not trust the classification of traffic that it receives. To disable trusted boundary, use the no mls qos trust device interface configuration command If you enter the mls qos cos override interface configuration command, the port does not trust the classification of the traffic that it receives, even when it is connected to a Cisco IP phone. Table 26-2 lists the port configuration when an IP phone is present or absent. 26-14 Catalyst 2950 Desktop Switch Software Configuration Guide 78-14982-01