The answer is a police action configured with a drop exceed-action that discards traffic exceeding the committed information rate. This is correct because policing is a congestion avoidance mechanism that drops packets immediately when the rate surpasses the CIR, regardless of queue depth or available bandwidth, unlike CBWFQ queuing which manages congestion through scheduling. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this scenario tests your ability to distinguish between policing and shaping, with a common trap being to blame the CBWFQ queue configuration when the real culprit is a policer applied to the premium class. Remember that policing drops before queuing, so if only one class sees drops on a congested link, suspect a per-class policer rather than a queue depth issue. A useful memory tip: "Police drop before the queue, shaping holds the queue."
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.
An SP's core router experiences excessive packet drops on a congested link. The QoS policy uses CBWFQ with 4 queues. The drops occur only in the queue for a premium business class. Which is the most likely cause?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The premium class is configured with a police action that drops traffic when it exceeds the committed information rate.
The premium business class queue is experiencing excessive packet drops because a police action configured with a 'drop' exceed-action is discarding traffic that exceeds the committed information rate (CIR). Unlike congestion management (queuing), policing is a congestion avoidance mechanism that drops packets immediately when the traffic rate surpasses the configured CIR, regardless of the queue depth or available bandwidth. This explains why drops occur only in the premium class queue, as the policer is explicitly dropping excess packets before they even enter the CBWFQ scheduler.
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.
✗
The 'bandwidth remaining' command is missing from the policy-map.
Why it's wrong here
That affects sharing of excess bandwidth, not dropping within a class.
✗
The interface is using MLP with interleaving.
Why it's wrong here
MLP interleaving is for link fragmentation and interleaving, not queue drops.
✗
The queue is using tail-drop without WRED.
Why it's wrong here
Tail-drop can cause drops, but the question specifies only that queue; WRED might help.
✓
The premium class is configured with a police action that drops traffic when it exceeds the committed information rate.
Why this is correct
Policing drops excess traffic; if the police rate is lower than the guaranteed bandwidth, drops occur.
Clue confirmation
The clue word "most likely" 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
Cisco often tests the distinction between policing (which drops excess traffic regardless of congestion) and queuing (which drops only when buffers are full), leading candidates to mistakenly attribute drops to congestion management mechanisms like tail-drop or WRED when the real cause is a police action configured with a drop exceed-action.
Detailed technical explanation
How to think about this question
Policing uses a token bucket algorithm to enforce a traffic rate; when the token bucket is empty, packets are either dropped (for 'drop' exceed-action) or remarked (for 'set' exceed-action). In contrast, CBWFQ queues use tail-drop or WRED to manage congestion only when the queue depth exceeds configured thresholds. A common real-world scenario is a service provider using a two-rate policer (CIR and PIR) on a premium class to enforce a strict bandwidth contract, where any burst above the CIR is dropped to prevent SLA violations, causing drops even when the link is not congested.
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: The premium class is configured with a police action that drops traffic when it exceeds the committed information rate. — The premium business class queue is experiencing excessive packet drops because a police action configured with a 'drop' exceed-action is discarding traffic that exceeds the committed information rate (CIR). Unlike congestion management (queuing), policing is a congestion avoidance mechanism that drops packets immediately when the traffic rate surpasses the configured CIR, regardless of the queue depth or available bandwidth. This explains why drops occur only in the premium class queue, as the policer is explicitly dropping excess packets before they even enter the CBWFQ scheduler.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". 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.
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Question Discussion
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