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Catalyst 3750 Switch Software Configuration Guide
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Chapter 32 Configuring QoS
Configuring Standard QoS
CoS setting). By contrast, trusted boundary uses 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. Note that the trusted boundary feature is not effective if the PC and Cisco IP Phone
are connected to a hub that is connected to the switch.
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 mls qos trust device interface configuration
command.
Configuring the DSCP Trust State on a Port Bordering Another QoS Domain
If you are administering two separate QoS domains between which you want to implement QoS features
for IP traffic, you can configure the switch ports bordering the domains to a DSCP-trusted state as shown
in Figure 32-12. Then the receiving port accepts the DSCP-trusted value and avoids the classification
stage of QoS. If the two domains use different DSCP values, you can configure the
DSCP-to-DSCP-mutation map to translate a set of DSCP values to match the definition in the other
domain.
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
the 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 (auto 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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