CCNP Network Function Virtualization Practice Question
This 350-401 practice question tests your understanding of network function virtualization. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network team must design a QoS policy for a WAN link that carries voice, video, and data. The policy must ensure that voice traffic is never dropped, even during congestion. Which queuing mechanism should be used for the voice class?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "never"
Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
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).
Low-latency queuing (LLQ) is the correct choice because it combines strict priority queuing with CBWFQ, allowing voice traffic to be placed in a strict priority queue that is serviced first before any other queues. This ensures that voice packets are never dropped due to congestion, as long as the configured policer rate is not exceeded, meeting the requirement that voice traffic is never dropped.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Class-based weighted fair queuing (CBWFQ).
Why it's wrong here
CBWFQ provides bandwidth guarantees but no strict priority, so voice may be dropped.
✓
Low-latency queuing (LLQ).
Why this is correct
LLQ combines strict priority with CBWFQ, ensuring voice is never dropped.
Clue confirmation
The clue word "never" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Weighted random early detection (WRED).
Why it's wrong here
WRED is a congestion avoidance mechanism, not a queuing mechanism.
✗
First-in, first-out (FIFO) queuing.
Why it's wrong here
FIFO does not provide any priority for voice traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that CBWFQ alone can provide low latency for voice, but the trap is that CBWFQ lacks a strict priority queue, so only LLQ guarantees zero drops for real-time traffic during congestion.
Detailed technical explanation
How to think about this question
LLQ uses a strict priority queue (PQ) that is policed by a configurable bandwidth limit (e.g., 'priority 256' under a class map) to prevent starvation of other traffic; if voice traffic exceeds the policer, excess packets are dropped rather than queued, preserving the priority queue's low latency. In real-world deployments, the priority queue is typically serviced by the hardware scheduler before any CBWFQ queues, ensuring sub-10ms delay for voice, but misconfiguration of the policer (e.g., setting it too low) can cause unexpected drops during peak call volumes.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 350-401 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Function Virtualization — This question tests Network Function Virtualization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Low-latency queuing (LLQ). — Low-latency queuing (LLQ) is the correct choice because it combines strict priority queuing with CBWFQ, allowing voice traffic to be placed in a strict priority queue that is serviced first before any other queues. This ensures that voice packets are never dropped due to congestion, as long as the configured policer rate is not exceeded, meeting the requirement that voice traffic is never dropped.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "never". Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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