An engineer wants the wireless voice traffic class of service to be used to determine the queue order for packets received, and then have the differentiated services code point set to match when it is resent to another port on the switch. Which configuration is required in the network?

“mls qos trust cos” tells the switch to accept (trust) the 802.1p CoS value that arrives from the WLC/AP, use that value to choose the internal queue, and then rewrite the packet’s DSCP on egress via the default cos-to-dscp map. Thus queueing is driven by the received CoS and the DSCP sent toward the next hop is automatically set to the equivalent value—exactly the behavior requested.

A. Platinum QoS defines WLAN profile settings on the WLC but does not influence how the downstream switch classifies or rewrites DSCP.
B. WMM required allows 802.11e prioritization over the air only; it does not control switch port trust or DSCP rewriting.
C. “mls qos trust dscp” ignores the incoming CoS and queues on DSCP, opposite of the requirement to base queuing on CoS.

1. Cisco Catalyst 3850 Switch QoS Configuration Guide

IOS-XE 16.12

“mls qos trust cos”

Section ‘Configuring Port Trust’; p.7-9.

2. Cisco Enterprise Mobility 8.3 Design Guide

Chapter “Wired QoS for WLAN Controllers and APs”

Table 15-2: “Use mls qos trust cos so the switch trusts the CoS and rewrites DSCP.”

3. Cisco IOS Quality of Service Solutions Configuration Guide

Release 15-M&T

“How to Configure QoS Using MQC”

‘COS-DSCP Mapping’; p.3-37 – 3-39.