- A
Voice traffic is being marked with EXP 4 but the priority queue also includes EXP 5, which may cause policing.
Why wrong: Incorrect. Including EXP 5 does not directly cause voice drops unless there is a policer.
- B
The bandwidth queue for video is configured to borrow from the priority queue.
Why wrong: Incorrect. Borrowing is not a standard feature; priority queues are typically not borrowed from.
- C
The priority queue is not strictly priority; it shares bandwidth with other queues.
Why wrong: Incorrect. A priority queue is typically strict priority, so voice should be serviced first.
- D
The priority queue is rate-limited by a policer that shapes traffic to a certain bandwidth.
Correct. Many implementations use a policer on the priority queue to prevent starvation; if the police rate is too low, voice packets are dropped.
Quick Answer
The answer is that the priority queue is rate-limited by a policer, which drops voice packets during bursts. In strict priority queuing, a priority queue (PQ) will service all its packets before any other queue, so voice should never be dropped due to congestion alone. However, service providers commonly apply a policer to the PQ to prevent it from starving lower-priority queues—if that policer’s committed information rate is set too low, any traffic exceeding that rate is dropped, even though the queue itself is not congested. This scenario tests your understanding of how QoS priority queue policer drops interact with MPLS EXP-based marking in a Cisco SPCOR / CCNP Service Provider Core 350-501 exam context. A common trap is assuming a strict priority queue never drops; the exam expects you to recognize that policing is the hidden mechanism causing the loss. Memory tip: “PQ with a policer is like a VIP lane with a bouncer—priority gets in, but only up to the bouncer’s limit.”
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. 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 SP is deploying a Quality of Service (QoS) architecture in its core network to support multiple services: voice, video, and data. The core routers use MPLS and implement QoS based on the MPLS EXP bits. The architecture must ensure that voice packets are never dropped, even during congestion, while allowing video to have higher priority than data. The current design marks voice with EXP 4, video with EXP 3, and data with EXP 0. During a traffic burst, voice traffic is being dropped, which should not happen. The core routers have the following queue configuration: (1) a priority queue (PQ) for EXP 4+5, (2) a bandwidth queue for EXP 2-3, (3) a default queue for EXP 0-1. What is most likely the cause of voice drops?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 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
The priority queue is rate-limited by a policer that shapes traffic to a certain bandwidth.
Voice drops occur because the priority queue is often rate-limited by a policer to prevent starvation of other queues. If the policer rate is set too low, voice packets are dropped during bursts. Strict priority without policing does not drop, but policing is common in SP core to protect other queues. The bandwidth queue and default queue are not the issue.
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.
- ✗
Voice traffic is being marked with EXP 4 but the priority queue also includes EXP 5, which may cause policing.
Why it's wrong here
Incorrect. Including EXP 5 does not directly cause voice drops unless there is a policer.
- ✗
The bandwidth queue for video is configured to borrow from the priority queue.
Why it's wrong here
Incorrect. Borrowing is not a standard feature; priority queues are typically not borrowed from.
- ✗
The priority queue is not strictly priority; it shares bandwidth with other queues.
Why it's wrong here
Incorrect. A priority queue is typically strict priority, so voice should be serviced first.
- ✓
The priority queue is rate-limited by a policer that shapes traffic to a certain bandwidth.
Why this is correct
Correct. Many implementations use a policer on the priority queue to prevent starvation; if the police rate is too low, voice packets are dropped.
Clue confirmation
The clue words "most likely", "never" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 350-501 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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Architecture — study guide chapter
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FAQ
Questions learners often ask
What does this 350-501 question test?
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The priority queue is rate-limited by a policer that shapes traffic to a certain bandwidth. — Voice drops occur because the priority queue is often rate-limited by a policer to prevent starvation of other queues. If the policer rate is set too low, voice packets are dropped during bursts. Strict priority without policing does not drop, but policing is common in SP core to protect other queues. The bandwidth queue and default queue are not the issue.
What should I do if I get this 350-501 question wrong?
Identify which 350-501 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "never". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 24, 2026
This 350-501 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 350-501 exam.
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