Cisco 2950 Software Configuration Guide - Page 585
Enabling Pass-Through Mode, Port Configuration, When a Cisco IP Phone is Present, Command, Purpose
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Chapter 30 Configuring QoS Configuring Standard QoS You cannot enable trusted boundary if auto-QoS is already enabled and vice-versa. If auto-QoS is enabled and a Cisco IP Phone is absent on a port, the port does not trust the classification of traffic that it receives. Table 30-6 lists the port configuration when an IP phone is present or absent. Table 30-6 Port Configurations When Trusted Boundary is Enabled Port Configuration When a Cisco IP Phone is Present When a Cisco IP Phone is Absent The port trusts the CoS value The packet CoS value is trusted. The packet CoS value is assigned of the incoming packet. the default CoS value. The port trusts the DSCP The packet DSCP value is trusted. For tagged non-IP packets, the value of the incoming packet. packet CoS value is set to 0. For untagged non-IP packets, the packet CoS value is assigned the default CoS value. The port assigns the default CoS value to incoming packets. The packet CoS value is assigned The packet CoS value is assigned the default CoS value. the default CoS value. Enabling Pass-Through Mode In software releases earlier than Cisco IOS Release 12.1(11)EA1, the switch is in pass-through mode. It uses the CoS value of incoming packets without modifying the DSCP value and sends the packets from one of the four egress queues. You cannot enable or disable pass-through mode if your switch is running a software release earlier than Cisco IOS Release 12.1(11)EA1. In Cisco IOS Release 12.1(11)EA1 or later, the switch assigns a CoS value of 0 to all incoming packets without modifying the packets. The switch offers best-effort service to each packet regardless of the packet contents or size and sends it from a single egress queue. Beginning in privileged EXEC mode, follow these steps to enable pass-through mode: Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Command Purpose configure terminal Enter global configuration mode. interface interface-id Specify the interface on which pass-through mode is enabled, and enter interface configuration mode. Valid interfaces include physical interfaces. mls qos trust cos pass-through dscp Enable pass-through mode. The interface is configured to trust the CoS value of the incoming packets and to send them without modifying the DSCP value. end Return to privileged EXEC mode. show mls qos interface [interface-id] Verify your entries. copy running-config startup-config (Optional) Save your entries in the configuration file. 78-11380-10 Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 30-25
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