Which QoS mechanism lets an administrator enforce a maximum traffic rate on an interface?

Policing is the correct answer because it actively monitors traffic flow and drops packets that exceed a configured rate, thereby enforcing a maximum traffic rate. This is often used to protect network resources from excessive traffic or to ensure compliance with service level agreements (SLAs). Marking, on the other hand, changes the QoS label (e.g., DSCP or CoS) of a packet but doesn't control its rate. Queueing manages how packets are buffered and transmitted when congestion occurs, but it doesn't enforce a hard rate limit. Classification identifies and categorizes traffic based on various criteria, which is a prerequisite for applying other QoS mechanisms, but it doesn't itself enforce a rate.