350-501 Automation and Quality of Service Practice Question
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?
⚠ Common exam trap
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.
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 shape rate is too low; increase it to match the access link speed (e.g., 20 Mbps).
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.
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.
- ✗
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.
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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.