- A
FIFO (First In, First Out) with tail drop
Why wrong: FIFO does not provide any priority or bandwidth guarantees; all traffic is treated equally.
- B
CBWFQ (Class-Based Weighted Fair Queuing) without a priority queue
Why wrong: CBWFQ can guarantee bandwidth per class but does not provide a strict priority queue for voice, which would cause jitter.
- C
LLQ (Low Latency Queuing) with a strict priority queue for voice and CBWFQ for video and data
LLQ combines a strict priority queue (for voice) with CBWFQ classes (for video and data), meeting both latency and bandwidth requirements.
- D
WRED (Weighted Random Early Detection) with DSCP-based drop probabilities
Why wrong: WRED is a congestion avoidance mechanism, not a queuing strategy; it does not provide priority or bandwidth guarantees.
Quick Answer
The correct choice is LLQ (Low Latency Queuing) with a strict priority queue for voice and CBWFQ for video and data. This combination works because LLQ provides a dedicated priority queue that ensures voice traffic is always served first, eliminating jitter and delay, while CBWFQ guarantees a minimum bandwidth allocation for video and allows best-effort traffic to use any remaining capacity. On the ENCOR 350-401 exam, this scenario tests your understanding that CBWFQ alone cannot meet strict priority requirements for real-time traffic, making LLQ the essential addition for voice and video queuing over limited WAN links. A common trap is selecting CBWFQ by itself, forgetting that it lacks a priority mechanism. To remember, think of LLQ as “CBWFQ with a fast lane”—the priority queue is the express pass for voice, while CBWFQ handles the rest.
350-401 Enterprise Network Design Practice Question
This 350-401 practice question tests your understanding of enterprise network design. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An enterprise is redesigning its WAN QoS architecture to support real-time voice, video, and critical data applications over a limited bandwidth link. The architect must ensure that voice traffic receives strict priority queuing and that video traffic is guaranteed a minimum bandwidth, while allowing best-effort traffic to use remaining capacity. Which queuing strategy should be deployed on the WAN edge routers?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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
LLQ (Low Latency Queuing) with a strict priority queue for voice and CBWFQ for video and data
LLQ combines a strict priority queue for delay-sensitive voice traffic with CBWFQ for other classes, guaranteeing minimum bandwidth for video while allowing best-effort traffic to share remaining capacity. This satisfies the requirement for strict priority queuing for voice and bandwidth guarantees for video, which CBWFQ alone cannot provide because it lacks a priority queue.
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.
- ✗
FIFO (First In, First Out) with tail drop
Why it's wrong here
FIFO does not provide any priority or bandwidth guarantees; all traffic is treated equally.
- ✗
CBWFQ (Class-Based Weighted Fair Queuing) without a priority queue
Why it's wrong here
CBWFQ can guarantee bandwidth per class but does not provide a strict priority queue for voice, which would cause jitter.
- ✓
LLQ (Low Latency Queuing) with a strict priority queue for voice and CBWFQ for video and data
Why this is correct
LLQ combines a strict priority queue (for voice) with CBWFQ classes (for video and data), meeting both latency and bandwidth requirements.
Clue confirmation
The clue words "best", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
WRED (Weighted Random Early Detection) with DSCP-based drop probabilities
Why it's wrong here
WRED is a congestion avoidance mechanism, not a queuing strategy; it does not provide priority or bandwidth guarantees.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between CBWFQ and LLQ, trapping candidates who think CBWFQ alone can provide strict priority queuing, when in fact only LLQ adds the 'priority' keyword to create a low-latency queue.
Detailed technical explanation
How to think about this question
LLQ uses a single strict priority queue policed by a configurable bandwidth limit (e.g., 'priority 256' under a class map) to prevent starvation of other queues, while CBWFQ classes use weighted fair queuing with bandwidth percentages or bandwidth remaining ratios. In real-world deployments, voice traffic is marked with EF (DSCP 46) and placed into the priority queue, while video (e.g., AF41) is assigned a guaranteed bandwidth via the 'bandwidth' command; the priority queue is policed to ensure that bursts do not exceed the configured rate, protecting other classes from being starved.
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.
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Enterprise Network Design — study guide chapter
Learn the concepts, then practise the questions
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Enterprise Network Design practice questions
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FAQ
Questions learners often ask
What does this 350-401 question test?
Enterprise Network Design — This question tests Enterprise Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: LLQ (Low Latency Queuing) with a strict priority queue for voice and CBWFQ for video and data — LLQ combines a strict priority queue for delay-sensitive voice traffic with CBWFQ for other classes, guaranteeing minimum bandwidth for video while allowing best-effort traffic to share remaining capacity. This satisfies the requirement for strict priority queuing for voice and bandwidth guarantees for video, which CBWFQ alone cannot provide because it lacks a priority queue.
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: "best", "minimum / minimize". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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.
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