The correct answer is LLQ with a priority queue for voice and a default class for data. This configuration works because Low Latency Queuing (LLQ) places voice traffic into a strict priority queue, guaranteeing both bandwidth and low latency during congestion, while the default class uses Class-Based Weighted Fair Queuing (CBWFQ) to allocate remaining bandwidth to data traffic without starving it entirely—the priority queue is policed to prevent voice from monopolizing all resources. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of MPLS-TE tunnel QoS, where engineers often mistakenly apply a simple priority queue without policing, risking data starvation. A common trap is assuming that a priority queue alone is sufficient, but LLQ’s policing mechanism is critical for balancing voice priority with data fairness. Remember the mnemonic “Voice VIP, but with a cap”—LLQ gives voice priority, but the police keeps data alive.
350-501 Automation and Quality of Service Practice Question
This 350-501 practice question tests your understanding of automation and quality of service. 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 service provider uses an MPLS-TE tunnel to carry voice and data traffic. The tunnel is experiencing packet loss during congestion. The engineer wants to ensure that voice traffic receives guaranteed bandwidth and low latency while data traffic uses remaining bandwidth. Which QoS configuration should be applied on the tunnel interface?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
LLQ with a priority queue for voice and a default class for data
Option A is correct because Low Latency Queuing (LLQ) allows you to place voice traffic into a strict priority queue, ensuring guaranteed bandwidth and low latency during congestion, while the default class uses CBWFQ to allocate remaining bandwidth to data traffic. This matches the requirement of prioritizing voice without starving data entirely, as the priority queue is policed to prevent voice from consuming all bandwidth.
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.
✓
LLQ with a priority queue for voice and a default class for data
Why this is correct
LLQ ensures low latency for voice, and the default class uses remaining bandwidth for data.
Related concept
Read the scenario before looking for a memorised answer.
✗
CBWFQ with bandwidth allocation for voice and data
Why it's wrong here
CBWFQ does not provide strict priority for voice, potentially causing latency.
✗
Policing on voice traffic to limit its rate
Why it's wrong here
Policing discards excess traffic but does not guarantee bandwidth or low latency.
✗
Shaping on the tunnel to 75% of bandwidth with no queuing
Why it's wrong here
Shaping without queuing does not prioritize voice over data.
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 here is that CBWFQ lacks a strict priority queue, so voice traffic will experience delay and jitter, making LLQ the only correct choice for real-time traffic.
Detailed technical explanation
How to think about this question
LLQ combines a strict priority queue (PQ) with Class-Based Weighted Fair Queuing (CBWFQ) for other classes; the priority queue is policed by default to a configured bandwidth (e.g., 'priority 64' for 64 kbps) to prevent starvation of other queues. In MPLS-TE tunnels, QoS policies are applied to the tunnel interface itself, and the tunnel's bandwidth can be explicitly reserved using the 'bandwidth' command under the tunnel interface to match the TE reservation. A real-world scenario is a service provider using DiffServ-aware TE (DS-TE) to map voice to the priority class and data to the best-effort class, ensuring SLA compliance.
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 350-501 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.
Automation and Quality of Service — This question tests Automation and Quality of Service — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: LLQ with a priority queue for voice and a default class for data — Option A is correct because Low Latency Queuing (LLQ) allows you to place voice traffic into a strict priority queue, ensuring guaranteed bandwidth and low latency during congestion, while the default class uses CBWFQ to allocate remaining bandwidth to data traffic. This matches the requirement of prioritizing voice without starving data entirely, as the priority queue is policed to prevent voice from consuming all bandwidth.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network engineer notices that voice traffic is being dropped during congestion. The traffic is marked with DSCP EF. After reviewing the QoS policy, it is discovered that the voice traffic is not being placed into a priority queue. Which configuration change would ensure voice traffic receives priority treatment?
easy
A.Increase the queue limit to 1000 packets
B.Increase the bandwidth percentage for the voice class
C.Enable WRED on the voice class
✓ D.Add the 'priority' command under the voice class in the policy map
Why D: DSCP EF (Expedited Forwarding, per RFC 3246) requires strict priority queuing to guarantee low latency and jitter for voice traffic. The 'priority' command under the voice class in a policy map places the traffic into a strict priority queue (LLQ), ensuring it is serviced before any other queue during congestion. Without this command, the voice traffic is treated as a regular class, subject to bandwidth constraints and potential drops.
Variation 2. An SP engineer implements LLQ for VoIP traffic on a DS3 link. The policy-map calls for a priority queue of 500 kbps. The actual VoIP traffic averages 400 kbps with bursts to 600 kbps. What is the expected behavior during bursts?
easy
A.The excess traffic is reclassified to best-effort and placed in the default queue.
B.The priority queue uses tail-drop and discards only when the queue is full.
✓ C.The priority queue drops all traffic above the configured 500 kbps during the burst.
D.The excess traffic is queued in the priority queue until bandwidth is available.
Why C: C is correct because the priority queue in a Low Latency Queueing (LLQ) policy is policed at the configured rate (500 kbps). When VoIP traffic bursts exceed this rate, the excess packets are dropped immediately by the policer, not queued or reclassified. This ensures that the priority queue does not starve other queues and maintains low latency for conforming traffic.
Last reviewed: Jun 11, 2026
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