350-501 Automation and Quality of Service Practice Question
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?
⚠ Common exam trap
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.
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.
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.
- ✗
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.
Go deeper
Related to this question
About these practice questions
This 350-501 question is part of Courseiva's 971-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.