350-501 Automation and Quality of Services Practice Question
An SP network engineer needs to implement hierarchical QoS on a PE router to shape customer traffic to a contracted rate of 10 Mbps while providing priority for voice traffic and bandwidth guarantee for critical data. Which MQC configuration correctly achieves this?
⚠ Common exam trap
A common mix-up: candidates assume a single policy-map can combine shape and priority/bandwidth, but Cisco specifically tests that hierarchical QoS is mandatory when you need to shape an aggregate rate while applying per-class queuing actions, as shape average in a flat policy acts per-class, not on the total traffic.
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
✓
Create a child policy with class-maps for voice and data; create a parent policy that applies the child policy and shapes to 10 Mbps; apply parent policy to the interface.
Hierarchical QoS (HQoS) is required when you need to shape traffic to a contracted rate (e.g., 10 Mbps) while also applying per-class actions like priority and bandwidth guarantees. Option A correctly uses a child policy to define class-based QoS (priority for voice, bandwidth for critical data) and a parent policy that applies the shape average command to the entire child policy aggregate, enforcing the 10 Mbps contract. This two-level MQC structure ensures that shaping occurs at the parent level before the child policy’s per-class queuing and scheduling are applied.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Create a child policy with class-maps for voice and data; create a parent policy that applies the child policy and shapes to 10 Mbps; apply parent policy to the interface.
Why this is correct
This is the correct hierarchical QoS design: child policy handles classification and queuing, parent policy shapes the aggregate traffic.
- ✗
Apply a service-policy out with shape and then apply another service-policy in with priority; both on the same interface.
Why it's wrong here
Two service policies on the same interface in the same direction is not supported; hierarchical QoS uses one policy applied to the interface.
- ✗
Apply a single policy-map that includes both shape and priority; no hierarchy needed.
Why it's wrong here
Single-level policy cannot simultaneously shape and provide per-class queuing; hierarchical QoS is required.
- ✗
Use a policy-map with shape average 10 Mbps and then use the bandwidth command for voice and data classes; no hierarchy.
Why it's wrong here
Shaping at the same level as queuing can cause conflicts; hierarchical QoS is needed to separate shaping and queuing.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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