The answer is that the shape rate of 10 Mbps is too low and should be increased to match the access link speed, such as 20 Mbps. This is correct because shaping introduces a single token bucket that queues all traffic—including critical-data—when the aggregate load exceeds the configured rate, causing excessive delay even if individual class queues are not full. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding that shaping creates a bottleneck at the interface level, not just within class queues, and that high latency from shaping is often mistaken for a policing or bandwidth allocation issue. A common trap is to blame the critical-data class bandwidth guarantee, but the real culprit is the shaper itself, which serializes packets and adds queuing delay for all traffic during peak hours. Remember the memory tip: “Shape the link, not the class—if latency spikes, check the ceiling first.”
350-501 Automation and Quality of Service Practice Question
This 350-501 practice question tests your understanding of automation and quality of service. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
A large enterprise recently implemented centralized QoS policies using Cisco DNA Center. The policies are pushed via RESTCONF to the branch routers. After the deployment, the branch office reports that critical business applications (like ERP) are being delayed. The network team verifies that the QoS policy is applied correctly on the WAN interface (Serial0/0/0) with a shape of 10 Mbps. The policy-map has a class for 'critical-data' with bandwidth 5 Mbps and another class for 'transactional-data' with bandwidth 3 Mbps. The remaining traffic is in class-default with fair-queue. The branch router's CPU utilization is normal. The interface output shows that the queue for critical-data is rarely full, but packets are experiencing high latency. The engineer pings from the branch server to the central site and sees 200 ms RTT normally, but up to 500 ms during peak hours. What is the most likely cause of the high latency for critical-data?
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 shape rate is too low; increase it to match the access link speed (e.g., 20 Mbps).
The correct answer is A because the shape rate of 10 Mbps is the bottleneck. Even though the critical-data class has a bandwidth guarantee of 5 Mbps, the overall interface is shaped to 10 Mbps. During peak hours, when the sum of all traffic (critical, transactional, and default) exceeds 10 Mbps, packets are queued at the shaper. This queueing introduces additional delay (up to 500 ms) for all classes, including critical-data, because the shaper enforces a single token bucket for the entire interface. Increasing the shape rate to match the actual access link speed (e.g., 20 Mbps) would reduce the queuing delay by allowing more traffic to be transmitted immediately.
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 shape rate is too low; increase it to match the access link speed (e.g., 20 Mbps).
Why this is correct
If shaped to 10 Mbps but the actual link is faster, traffic buffers, increasing latency. Increasing shape rate reduces buffering.
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.
✗
The critical-data class needs a priority command to reduce latency.
Why it's wrong here
Priority would cause drops if policed, not necessarily reduce latency; bandwidth already works.
✗
The queue-limit for critical-data is too high; reduce it to force early drops.
Why it's wrong here
Reducing queue-limit would cause drops, not reduce latency for surviving packets.
✗
The bandwidth command in critical-data should be increased above 5 Mbps.
Why it's wrong here
Bandwidth alone does not reduce latency; it only guarantees minimum during congestion.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between shaping and policing, and the trap here is that candidates assume the bandwidth command inside a class provides low latency, when in fact a shaper at the interface level introduces queuing delay for all traffic, regardless of class-level guarantees.
Detailed technical explanation
How to think about this question
When a shaper is applied to an interface, it uses a token bucket to limit the output rate. If traffic exceeds the shape rate, packets are queued in the shaper's buffer, which introduces serialization delay and queuing delay. The bandwidth command inside a policy-map only guarantees a minimum bandwidth during congestion, but it does not bypass the shaper's token bucket. In this scenario, the shaper is the first point of queueing, so all classes experience the same shaping delay. A common real-world mistake is to focus on class-level tuning while ignoring the parent shaper, which is the actual bottleneck.
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 shape rate is too low; increase it to match the access link speed (e.g., 20 Mbps). — The correct answer is A because the shape rate of 10 Mbps is the bottleneck. Even though the critical-data class has a bandwidth guarantee of 5 Mbps, the overall interface is shaped to 10 Mbps. During peak hours, when the sum of all traffic (critical, transactional, and default) exceeds 10 Mbps, packets are queued at the shaper. This queueing introduces additional delay (up to 500 ms) for all classes, including critical-data, because the shaper enforces a single token bucket for the entire interface. Increasing the shape rate to match the actual access link speed (e.g., 20 Mbps) would reduce the queuing delay by allowing more traffic to be transmitted immediately.
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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