CCNP Infrastructure Practice Question
A network engineer is implementing QoS on a Cisco IOS router. The engineer wants to ensure that VoIP traffic is prioritized and that excess VoIP traffic is dropped when the interface is congested. Which QoS mechanism should be used?
⚠ Common exam trap
The trap here is thinking that CBWFQ or shaping can handle VoIP prioritization, but only LLQ with a policer provides both strict priority and drop of excess traffic.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Low Latency Queuing (LLQ) with a policer.
For VoIP, LLQ provides a strict priority queue to minimize latency and jitter. To prevent excess VoIP traffic from starving other queues, a policer is applied to the priority queue, dropping packets that exceed the configured rate. This combination ensures VoIP is prioritized and excess traffic is dropped during congestion.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Weighted Random Early Detection (WRED) on the VoIP class.
Why it's wrong here
WRED is a congestion avoidance mechanism that drops packets based on queue depth, but it is not typically used for strict priority traffic like VoIP. It does not provide the guaranteed low latency that VoIP requires and may drop packets prematurely, affecting voice quality.
- ✗
Class-Based Weighted Fair Queuing (CBWFQ) with a bandwidth guarantee.
Why it's wrong here
CBWFQ provides a minimum bandwidth guarantee but does not drop excess traffic when congestion occurs. It uses tail drop, which can cause global synchronization and is not ideal for VoIP. It does not provide the policing or shaping needed to drop excess VoIP traffic.
- ✗
Traffic shaping on the VoIP class.
Why it's wrong here
Traffic shaping buffers excess traffic rather than dropping it, which can introduce delay and jitter, degrading VoIP quality. Shaping is used to smooth traffic rates, not to drop excess VoIP traffic during congestion. It is not suitable for real-time traffic like voice.
- ✓
Low Latency Queuing (LLQ) with a policer.
Why this is correct
LLQ provides a strict priority queue for VoIP traffic, ensuring low latency and jitter. When combined with a policer, it can limit the amount of traffic that enters the priority queue, dropping excess VoIP packets during congestion. This meets the requirement to prioritize and drop excess VoIP traffic.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.