Question

A network engineer is deploying QoS on an access switch where Cisco IP phones connect to the switchport and PCs daisy-chain behind the phones. Company policy requires that the switch never trust any markings originating from the PCs, but it must honor the phone's CoS markings for voice and signaling. Which configuration approach on the access port correctly establishes the trust boundary?

Accepted Answer

Enable conditional trust with 'mls qos trust device cisco-phone' (or the auto QoS phone trust) so the switch trusts CoS only when a Cisco phone is detected via CDP, while the PC traffic is re-marked/untrusted

Answer

Configure 'mls qos trust dscp' on the switchport so all incoming DSCP values from both the phone and PC are preserved end to end

Answer

Disable QoS on the access port entirely and rely on the WAN router to classify and mark all voice and PC traffic centrally

Answer

Configure 'mls qos trust cos' unconditionally on the port so both the phone and any daisy-chained PC CoS values are always accepted