Cisco 2950 - Catalyst Switch Configuration Manual page 584

Configuring Standard QoS
With the trusted setting, you also can use the trusted boundary feature to prevent misuse of a
high-priority queue if a user bypasses the telephone and connects the PC directly to the switch. Without
trusted boundary, the CoS labels generated by the PC are trusted by the switch (because of the trusted
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 configure trusted boundary on a switch port:
Command
Step 1 configure terminal
Step 2
cdp enable
Step 3
interface interface-id
Step 4 cdp enable
Step 5 mls qos trust device cisco-phone
Step 6 mls qos trust cos
Step 7
end
Step 8
show mls qos interface [interface-id]
[policers]
Step 9 copy running-config startup-config
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.
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Purpose
Enter global configuration mode.
Enable CDP globally. By default, it is enabled.
Specify the interface to be trusted, and enter interface configuration
mode.
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.
You cannot enable both trusted boundary and auto-QoS (auto qos
voip interface configuration command) at the same time; they are
mutually exclusive.
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 Cisco IOS
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.
Chapter 30 Configuring QoS
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