Specifications

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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 27 Configuring QoS
Configuring Standard 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 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:
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.
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.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
cdp enable Enable CDP globally. By default, it is enabled.
Step 3
interface interface-id Enter interface configuration mode, and specify the interface to be
trusted.
Valid interfaces include physical interfaces.
Step 4
cdp enable Enable CDP on the interface. By default, CDP is enabled.
Step 5
mls qos trust device cisco-phone 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.
Step 6
mls qos trust cos 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 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.
Step 7
end Return to privileged EXEC mode.
Step 8
show mls qos interface [interface-id]
[policers]
Verify your entries.
Step 9
copy running-config startup-config (Optional) Save your entries in the configuration file.