Implementing and Operating Cisco Enterprise Network Core Technologies (ENCOR) v1.2InfrastructureMedium
A network engineer is troubleshooting slow application performance between two data centers. Packet captures show high latency and packet loss. The engineer suspects that the traffic is being treated as best-effort. The application uses UDP on port 5000. Which QoS mechanism should the engineer implement to ensure preferential treatment for this application traffic?
- ATraffic shaping
- BClassification and marking
- CTraffic policing
- DCongestion avoidance
Show answer & explanationAnswer & explanation
Correct answer: B. Classification and marking
To ensure preferential treatment, traffic must first be identified (classified) and then marked with a specific QoS value (e.g., DSCP) so that downstream devices can apply appropriate QoS policies like priority queuing or bandwidth guarantees.
Why the other options are wrong
- A. Traffic shaping buffers excess traffic to smooth out bursts, which is a congestion management tool, not the initial step for preferential treatment.
- C. Traffic policing drops or re-marks packets that exceed a configured rate, which is not the primary step for preferential treatment.
- D. Congestion avoidance (e.g., WRED) proactively drops packets to prevent congestion, which is a later QoS mechanism after traffic has been classified and marked.
QoS Classification & Marking
The process of identifying specific types of network traffic and assigning them a priority level or class.
- Classification identifies traffic based on criteria (e.g., port, protocol, IP address).
- Marking applies a QoS value (e.g., DSCP, CoS) to the packet header.
- Allows downstream devices to apply appropriate QoS policies.
Memory trick: Classify and Mark first, then manage the traffic flow.