Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureHard
A network engineer is troubleshooting a performance issue where a specific application's traffic experiences high latency and packet loss when traversing a congested WAN link. The application uses UDP on port 5000. The engineer needs to apply a QoS policy that marks this application's traffic with a specific DSCP value (e.g., EF for Expedited Forwarding) so that downstream devices can prioritize it. Which QoS component is responsible for identifying and marking specific traffic flows?
- AClassification and Marking
- BCongestion Avoidance
- CTraffic Shaping
- DCongestion Management
Show answer & explanationAnswer & explanation
Correct answer: A. Classification and Marking
Classification and Marking are the initial QoS components responsible for identifying specific traffic flows (e.g., UDP port 5000) and then assigning them a QoS label, such as a DSCP value. This marking allows subsequent QoS mechanisms (like queuing) to treat the traffic appropriately according to its priority.
Why the other options are wrong
- B. Congestion Avoidance proactively drops lower-priority traffic during congestion, relying on existing marks, but doesn't classify or mark.
- C. Traffic Shaping buffers and regulates traffic rates, acting on already classified and marked traffic, but doesn't perform initial identification or marking.
- D. Congestion Management (queuing) prioritizes traffic based on existing marks, but doesn't identify or mark it initially.
QoS Classification and Marking
The initial steps in a QoS policy where network traffic is identified (classified) based on various criteria and then assigned a QoS label (marked) for preferential treatment.
- Classification identifies traffic using ACLs, NBAR, etc.
- Marking applies DSCP, IP Precedence, or CoS.
- Enables downstream devices to apply QoS policies consistently.
Memory trick: First, you classify the cargo, then you mark it for special handling.