Cisco 2950G 24 - Catalyst Switch Software Configuration Manual page 532

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:
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.
Table 26-2
Catalyst 2950 Desktop Switch Software Configuration Guide
26-14
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
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.
lists the port configuration when an IP phone is present or absent.
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.
Chapter 26 Configuring QoS
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