notes: IP Phone Trust and CoS Extend

- ports are configured to trust the QoS marking only if the presence of a Cisco IP Phone is
sensed via CDP messages.
- If no Cisco device is detected on the port then the QoS markings are not trusted, even if the port is configured for trust.
- the switch may also instruct the IP Phone’s switch to apply specific CoS markings for frames received from the connected PC. The switch may either accept (trust) 802.1p bits received from the attached PC or enforce the instructed value. This feature particularly
makes sense to be used with the dot1p Voice VLAN option.

config-set:

interface FastEthernet0/6
mls qos trust cos
mls qos trust device cisco-phone
switchport priority extend cos 1


verification:

show mls qos interface #