On a Cisco Catalyst switch with an 802.1Q trunk configured mls qos trust dscp, how will ingress frames be classified for QoS treatment?

When mls qos trust dscp is configured on an interface, the switch is instructed to trust the Differentiated Services Code Point (DSCP) value in the IP header of incoming frames. This means the switch will use the DSCP value for QoS classification and subsequent treatment (e.g., queuing, policing). The 802.1Q Class of Service (CoS) value, which is part of the VLAN tag, is ignored for QoS classification when DSCP trust is enabled. If mls qos trust cos were configured, the CoS value would be used instead. Resetting DSCP values to 0 is not the default behavior for trust dscp. Mapping CoS to DSCP on ingress only happens if trust cos is enabled or if a specific QoS policy is applied for such mapping.