350-501 Automation and Quality of Service Practice Question
A network engineer is implementing QoS on a Cisco ASR 1000 for a customer with multiple service classes. The customer requires that mission-critical data not be starved when voice traffic bursts. Which two actions should the engineer take? (Choose two.)
⚠ Common exam trap
Cisco often tests the distinction between policing (which limits bandwidth) and shaping (which buffers and smooths traffic), and between bandwidth guarantees (which reserve capacity) and WRED (which manages congestion but does not prevent starvation), leading candidates to confuse these mechanisms.
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
✓
Configure a policer on the voice class to limit its bandwidth
Policing the voice class limits its bandwidth to a configured rate (e.g., using the `police` command under the class-map), preventing voice bursts from starving mission-critical data. This ensures that voice traffic does not exceed its allocated share, leaving enough bandwidth for other classes. Option D is correct because allocating a minimum bandwidth guarantee to the data class (e.g., using the `bandwidth` command under the class-map) ensures that even when voice bursts occur, the data class receives a reserved amount of bandwidth, preventing starvation. Together, these actions enforce admission control and bandwidth reservation, aligning with the customer's requirement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure a policer on the voice class to limit its bandwidth
Why this is correct
Policing the voice class prevents it from exceeding a set rate, protecting other classes from starvation.
- ✗
Enable WRED on the voice class
Why it's wrong here
WRED is for congestion avoidance; it is not appropriate for real-time voice traffic as it introduces drops.
- ✗
Use tail drop with a high threshold for the data class
Why it's wrong here
Tail drop does not guarantee bandwidth; it only drops packets when the queue is full.
- ✓
Allocate a minimum bandwidth guarantee to the data class
Why this is correct
A bandwidth guarantee ensures that the data class always receives a minimum amount of link capacity, even when voice bursts.
- ✗
Configure a shape on the voice class to 75% of interface bandwidth
Why it's wrong here
Shaping buffers traffic but does not drop; it is not typically used on real-time traffic due to added delay.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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