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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-08
Chapter 37 Configuring QoS
Configuring Standard QoS
In some situations, you can prevent a PC connected to the Cisco IP Phone from taking advantage of a
high-priority data queue. You can use the switchport priority extend cos interface configuration
command to configure the telephone through the switch CLI to override the priority of the traffic
received from the PC.
Beginning in privileged EXEC mode, follow these steps to enable trusted boundary on a port:
To disable the trusted boundary feature, use the no ml
s qos trust device interface configuration
command.
Enabling DSCP Transparency Mode
The switch supports the DSCP transparency feature. It affects only the DSCP field of a packet at egress.
By default, DSCP transparency is disabled. The switch modifies the DSCP field in an incoming packet,
and the DSCP field in the outgoing packet is based on the quality of service (QoS) configuration,
including the port trust setting, policing and marking, and the DSCP-to-DSCP mutation map.
If DSCP transparency is enabled by using the no
mls qos rewrite ip dscp command, the switch does not
modify the DSCP field in the incoming packet, and the DSCP field in the outgoing packet is the same as
that in the incoming packet.
Note Enabling DSCP transparency does not affect the port trust settings on IEEE 802.1Q tunneling ports.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
cdp run Enable CDP globally. By default, CDP is enabled.
Step 3
interface interface-id Specify the port connected to the Cisco IP Phone, and enter interface
configuration mode.
Valid interfaces include physical ports.
Step 4
cdp enable Enable CDP on the port. By default, CDP is enabled.
Step 5
mls qos trust cos
mls qos trust dscp
Configure the switch port to trust the CoS value in traffic received from the
Cisco IP Phone.
or
Configure the routed port to trust the DSCP value in traffic received from
th
e Cisco IP Phone.
By default, the port is not trusted.
Step 6
mls qos trust device cisco-phone Specify that the Cisco IP Phone is a trusted device.
You cannot enable both trusted boundary and auto-QoS (au
to qos voip
interface configuration command) at the same time; they are mutually
exclusive.
Step 7
end Return to privileged EXEC mode.
Step 8
show mls qos interface Verify your entries.
Step 9
copy running-config startup-config (Optional) Save your entries in the configuration file.
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