200-301 Question 389
Select 3A network engineer is tasked with ensuring consistent and predictable performance for a network link that experiences periodic congestion. The engineer decides to prioritize VoIP traffic while ensuring that large file transfers do not exceed a certain bandwidth limit. Which combination of traffic management techniques should the engineer implement to meet these requirements?
- A
Apply Class-Based Weighted Fair Queuing (CBWFQ) to prioritize VoIP traffic.
- B
Use traffic shaping to limit the outbound rate of large file transfers.
- C
Enable policing to drop excess VoIP traffic above the configured rate.
- D
Configure Weighted Random Early Detection (WRED) to reduce congestion.
- E
Use Low Latency Queuing (LLQ) to guarantee bandwidth for VoIP traffic.
Show answer and explanation
Correct answers: A, B, E
Explanation
To meet the requirements, the engineer must ensure VoIP traffic is prioritized while large file transfers are limited in bandwidth. CBWFQ and LLQ provide prioritization mechanisms, with LLQ being particularly effective for VoIP traffic. Traffic shaping is used to control the outbound rate for large file transfers, ensuring they do not overwhelm the link during periods of congestion. Policing and WRED are not optimal in this scenario as they do not align with the goal of ensuring predictable and consistent performance for both traffic types.
- A. Correct.
Class-Based Weighted Fair Queuing (CBWFQ) allows assigning bandwidth to specific traffic classes, which can help prioritize VoIP traffic. This is a valid technique for prioritization.
- B. Correct.
Traffic shaping ensures that large file transfers are rate-limited by buffering excess packets and sending them at a compliant rate. This is an appropriate method for controlling bandwidth usage.
- C. Incorrect.
Policing drops excess traffic beyond the configured rate, which may not be ideal for VoIP traffic as it can lead to packet loss and degraded call quality.
- D. Incorrect.
Weighted Random Early Detection (WRED) is a congestion avoidance mechanism that helps manage queue lengths but does not directly prioritize traffic or limit bandwidth.
- E. Correct.
Low Latency Queuing (LLQ) is specifically designed to prioritize delay-sensitive traffic like VoIP, ensuring that such traffic receives guaranteed bandwidth and minimal delay.