Explanation/Reference:
Section: Considerations for Expanding an Existing Network Explanation
Explanation:
According to Cisco best practices for implementing Quality of Service (QoS) in a campus LAN, traffic should be marked as close to its source as possible. Because the access layer provides direct connectivity to network endpoints, QoS classification and marking are typically performed in the access layer. Although classification and marking are typically performed in the access layer, QoS mechanisms must also be implemented throughout the network for QoS to be effective. In addition, best practice dictates that QoS mechanisms should be implemented in hardware whenever alternatives to software implementations are available.
Traffic policing is used to limit the rate of traffic that passes through an interface. With traffic policing, packet flows that exceed the configured thresholds are typically dropped. Alternatively, traffic can be remarked with a lower priority before being transmitted. Best practice dictates policing excess traffic as close to its source as possible so that no resources are wasted in transmitting packets that will ultimately be dropped.
Reference:
CCDA 200-310 Official Cert Guide, Chapter 3, Campus LAN QoS Considerations, pp. 111-112 Cisco: Enterprise Campus 3.0 Architecture: Overview and Framework: Principles of Campus QoS Design