CCNP Architecture Practice Question
A network engineer is designing a QoS policy for a WAN edge router. Voice traffic must be serviced with strict priority and guaranteed low latency, while a policer must limit voice to 30 percent of the interface bandwidth to prevent starvation of other queues. Which queuing mechanism should the engineer configure?
⚠ Common exam trap
The trap here is assuming that any bandwidth-guaranteeing queuing method provides strict priority, when only LLQ combines a strict priority queue with a policer to protect other traffic classes from starvation.
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 priority policer
Low Latency Queuing is the correct choice because it creates a strict priority queue for voice while applying a policer that caps the priority class at a configured rate, such as 30 percent of interface bandwidth. This gives voice minimal delay and jitter while preventing it from consuming all bandwidth. CBWFQ lacks strict priority, WRED is a drop mechanism, and FIFO offers no prioritization or policing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
First-In, First-Out (FIFO) queuing on the WAN interface
Why it's wrong here
FIFO queuing processes packets in the order they arrive without any priority or bandwidth guarantee. Voice packets could be delayed behind large data packets, causing jitter and poor call quality. FIFO also provides no mechanism to police voice traffic, so it cannot satisfy the strict priority and 30 percent limit requirements.
- ✗
Class-Based Weighted Fair Queuing (CBWFQ) with a bandwidth guarantee
Why it's wrong here
CBWFQ provides weighted bandwidth guarantees to each class but does not offer strict priority scheduling. Voice traffic placed in a CBWFQ class would compete with other classes according to weights, which can introduce jitter and delay. Since the requirement is strict priority for voice, CBWFQ alone does not meet the low-latency demand.
- ✗
Weighted Random Early Detection (WRED) on the voice class
Why it's wrong here
WRED is a congestion avoidance mechanism that drops packets early based on queue depth and IP precedence or DSCP. It is typically applied to TCP-based classes to prevent tail drop, but it does not provide strict priority scheduling. Applying WRED to voice would cause random drops and latency variation, which is unacceptable for real-time voice traffic.
- ✓
Low Latency Queuing (LLQ) with a priority policer
Why this is correct
Low Latency Queuing combines a strict priority queue for voice with a policer that caps the priority traffic at a configured rate, such as 30 percent of interface bandwidth. This ensures voice is serviced first with minimal delay while preventing the priority class from starving other queues if voice traffic exceeds the limit, exactly matching the design requirement.
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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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