Which QoS forwarding per-hop behavior changes a specific value in a packet header to set the class of service for the packet?

Shaping buffers traffic exceeding a configured rate and releases it in a controlled manner, preventing bursts but not modifying packet headers for CoS.

Classification identifies and categorizes traffic based on various criteria but does not alter the packet header itself.

Policing drops or re-marks traffic that exceeds a configured rate, enforcing limits but not primarily setting a class of service via header modification.

Marking is the QoS forwarding per-hop behavior that involves modifying a specific field in the packet header, such as the Differentiated Services Code Point (DSCP) in the IP header or the CoS field in the Ethernet header, to assign a class of service or priority level to the packet. This mark then tells subsequent network devices how to handle the packet based on its priority.