Quick Answer
The answer is single-rate two-color, as it is one of the three QoS mechanisms used for traffic policing, alongside single-rate three-color and dual-rate three-color. This is correct because traffic policing mechanisms rely on token bucket algorithms to measure and enforce traffic rates; the single-rate two-color model uses one token bucket to mark packets as either conforming (green) or exceeding (red), making it a fundamental policing implementation. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, you must distinguish between these token bucket variants, as the exam often tests your understanding of how dual-rate three-color (RFC 2698) uses two token buckets for committed and peak rates, while single-rate two-color (RFC 2697) uses only one. A common trap is confusing the number of colors with the number of buckets—remember, two colors means one bucket, three colors means two buckets. Memory tip: “One bucket, two colors; two buckets, three colors.”
This 350-501 practice question tests your understanding of automation and quality of service. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which THREE QoS mechanisms can be used for traffic policing?
dual-rate three-color
This is another common policing implementation.
token bucket
Token bucket is the underlying algorithm for policing.
single-rate two-color
This is a common policing implementation.
WRED
Why wrong: WRED is congestion avoidance, not policing.
shaping
Why wrong: Shaping buffers traffic, not policing.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
dual-rate three-color
Traffic policing uses token bucket mechanisms to measure and enforce traffic rates. Dual-rate three-color (RFC 2698) uses two token buckets (CIR/PIR) to mark packets as green, yellow, or red, allowing separate policing of committed and peak rates. Single-rate two-color (RFC 2697) uses one token bucket to mark packets as either conforming (green) or exceeding (red). Both are standard policing implementations.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
dual-rate three-color
Why this is correct
This is another common policing implementation.
Related concept
Read the scenario before looking for a memorised answer.
token bucket
Why this is correct
Token bucket is the underlying algorithm for policing.
Related concept
Read the scenario before looking for a memorised answer.
single-rate two-color
Why this is correct
This is a common policing implementation.
Related concept
Read the scenario before looking for a memorised answer.
WRED
Why it's wrong here
WRED is congestion avoidance, not policing.
shaping
Why it's wrong here
Shaping buffers traffic, not policing.
Common exam traps
Cisco often tests the distinction between policing and shaping, where candidates mistakenly select shaping as a policing mechanism because both control traffic rates, but shaping buffers while policing drops/re-marks.
Detailed technical explanation
Policing token buckets operate at line rate using a single or dual bucket model with configurable burst sizes (Bc, Be). For dual-rate three-color, the committed bucket (CIR/Bc) and peak bucket (PIR/Be) are refilled independently; packets exceeding PIR are dropped, while those between CIR and PIR are marked yellow. In Cisco IOS, policing is configured via the 'police' command under MQC, while shaping uses 'shape average' or 'shape peak'.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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Automation and Quality of Service — study guide chapter
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FAQ
Automation and Quality of Service — This question tests Automation and Quality of Service — Read the scenario before looking for a memorised answer..
The correct answer is: dual-rate three-color — Traffic policing uses token bucket mechanisms to measure and enforce traffic rates. Dual-rate three-color (RFC 2698) uses two token buckets (CIR/PIR) to mark packets as green, yellow, or red, allowing separate policing of committed and peak rates. Single-rate two-color (RFC 2697) uses one token bucket to mark packets as either conforming (green) or exceeding (red). Both are standard policing implementations.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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