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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapt er 26 Conf i gurin g QoS
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 po rt. If the te lephone is no t detect ed, the trusted bou ndary fea ture disab les the
trusted sett ing on the swi tch p ort an d p revents misu se of a h igh-p ri ority qu eu e.
Beginning in privileged EXEC mode, follow these ste ps to configure trusted boundary on a switch port:
When yo u enter the no mls qos trust interface conf iguration command, trusted boundary is not disabled.
If this co mmand is en tered a nd the port is connec ted 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 ente r the mls qos cos override interfac e configuration c omman d, the port doe s not trust the
classification of the traffic that it receives, even when it is connected to a Cisco IP phone.
Table 26-2 lists the por t configuratio n when an IP phone is present or a bsent.
Command Purpose
Step 1 configure terminal Enter g lo bal c onfigurat ion m ode.
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 Ci sco IP phon e as a truste d device on the inte rface.
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
refer enc e f or th is r el ea se.
Step 7 end Return to priv ileged 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.