- A
The police is using a token-bucket algorithm with a small burst size that is being exceeded
A small burst size means the bucket drains quickly, causing more packets to exceed the rate and be dropped, even if the long-term average is below the police rate.
- B
The police rate is configured in bits per second but the traffic is measured in bytes per second
Why wrong: This would cause a factor of 8, not 2, difference between configured and observed rates.
- C
The traffic is using a different DSCP value than expected
Why wrong: If the traffic is not matched by the class, it would be handled by class-default and not be subject to the police, so no drops would occur.
- D
The police action is set to drop, but the exceed-action is transmit
Why wrong: If exceed-action were transmit, no packets would be dropped; the observed drop rate would be zero.
Quick Answer
The answer is a token-bucket policer configured with a burst size that is too small for the incoming traffic pattern. When the burst size is insufficient, the token bucket empties rapidly under sustained traffic, causing the policer to drop exactly half the packets even though the average data rate remains below the configured police rate. This happens because the small burst size cannot accommodate natural micro-bursts, so the policer constantly marks packets as exceeding the rate, resulting in a precise 50% drop rate. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of how the single-rate two-color or two-rate three-color marker interacts with burst parameters—a common trap is to assume the police rate itself is misconfigured rather than the burst size. Remember the memory tip: “Half the rate, check the burst—small buckets drop first.”
350-501 Automation and Quality of Service Practice Question
This 350-501 practice question tests your understanding of automation and quality of service. 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.
While troubleshooting a customer complaint about slow data transfers, you notice that traffic from a specific site is being dropped. The QoS policy on the PE router includes a police command for the customer's traffic. The observed drop rate is exactly half of the configured police rate. What is the most probable reason?
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 police is using a token-bucket algorithm with a small burst size that is being exceeded
The observed drop rate being exactly half the configured police rate strongly suggests that the token-bucket algorithm is operating with a burst size that is too small. When the burst size is insufficient, the bucket empties quickly under sustained traffic, causing packets to be marked as exceeding the rate and dropped. The police command in Cisco IOS uses a single-rate two-color marker (RFC 2697) or a two-rate three-color marker (RFC 2698), and a small burst size leads to premature drops even when the average rate is below the configured police rate.
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 police is using a token-bucket algorithm with a small burst size that is being exceeded
Why this is correct
A small burst size means the bucket drains quickly, causing more packets to exceed the rate and be dropped, even if the long-term average is below the police rate.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The police rate is configured in bits per second but the traffic is measured in bytes per second
Why it's wrong here
This would cause a factor of 8, not 2, difference between configured and observed rates.
- ✗
The traffic is using a different DSCP value than expected
Why it's wrong here
If the traffic is not matched by the class, it would be handled by class-default and not be subject to the police, so no drops would occur.
- ✗
The police action is set to drop, but the exceed-action is transmit
Why it's wrong here
If exceed-action were transmit, no packets would be dropped; the observed drop rate would be zero.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that the police rate alone determines drops, but the trap here is that the burst size (bc/be) directly controls the token-bucket depth, and an undersized burst causes the policer to drop packets at a fixed ratio (e.g., 50%) even when the average rate is below the CIR.
Detailed technical explanation
How to think about this question
The token-bucket algorithm in Cisco's police command uses a committed burst (bc) and an excess burst (be) to determine conformance. If the burst size is set too small (e.g., bc = 1 packet), the bucket drains rapidly under sustained traffic, causing the policer to drop packets at exactly half the configured rate when the traffic pattern is constant (e.g., a CIR of 8 Mbps with a burst of 1500 bytes will drop every other packet for a 4 Mbps flow). In real-world scenarios, this is common when engineers copy-paste QoS configurations without adjusting burst parameters for the specific link speed or application.
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.
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Automation and Quality of Service — study guide chapter
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FAQ
Questions learners often ask
What does this 350-501 question test?
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 police is using a token-bucket algorithm with a small burst size that is being exceeded — The observed drop rate being exactly half the configured police rate strongly suggests that the token-bucket algorithm is operating with a burst size that is too small. When the burst size is insufficient, the bucket empties quickly under sustained traffic, causing packets to be marked as exceeding the rate and dropped. The police command in Cisco IOS uses a single-rate two-color marker (RFC 2697) or a two-rate three-color marker (RFC 2698), and a small burst size leads to premature drops even when the average rate is below the configured police rate.
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.
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Last reviewed: Jun 25, 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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