CCNP Architecture Practice Question
A network engineer is designing a QoS policy for a WAN edge router. The router must prioritize voice traffic with strict priority while ensuring that other traffic classes are not starved. The engineer decides to use Low Latency Queueing (LLQ). Which additional mechanism should be configured to prevent starvation of other queues when voice traffic exceeds its allocated bandwidth?
⚠ Common exam trap
The trap here is thinking that CBWFQ or shaping can prevent starvation, when the correct mechanism is a policer on the priority queue.
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
✓
Policing on the voice class to limit its bandwidth
LLQ provides a strict priority queue for voice, but without a policer, the priority queue can consume all available bandwidth and starve other queues. Configuring policing on the voice class limits the priority traffic to a defined rate, ensuring that other classes receive their configured bandwidth. This is the recommended practice for LLQ.
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 voice queue
Why it's wrong here
WRED is typically used on non-voice queues to manage congestion by dropping packets early. Applying WRED to the voice queue would be counterproductive because voice traffic is sensitive to drops and requires strict priority. WRED does not prevent starvation of other queues; it manages queue depth for TCP flows.
- ✗
Traffic shaping on the voice class to smooth bursts
Why it's wrong here
Traffic shaping buffers excess traffic to smooth bursts, but it does not prevent the priority queue from consuming all bandwidth. In fact, shaping the voice queue could introduce delay and jitter, which is harmful for voice. Shaping is not the mechanism used to prevent starvation in LLQ.
- ✓
Policing on the voice class to limit its bandwidth
Why this is correct
In LLQ, the priority queue is serviced first and can starve other queues if not policed. Configuring policing on the voice class limits the amount of traffic that can enter the priority queue, ensuring that other queues get bandwidth. This is the standard method to prevent starvation in LLQ deployments.
- ✗
Class-Based Weighted Fair Queueing (CBWFQ) on the voice class
Why it's wrong here
CBWFQ is used for non-priority classes to provide guaranteed bandwidth. The voice class in LLQ is already treated as a priority queue, so applying CBWFQ to it would conflict with the strict priority behavior. CBWFQ does not prevent starvation of other queues when the priority queue is oversubscribed.
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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
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