350-501 Automation and Quality of Service Practice Question
A service provider is automating QoS policy deployment using Cisco NSO and YANG. During validation, the engineer discovers that the pushed policy is not taking effect. Which three possible causes should be investigated? (Choose three.)
⚠ Common exam trap
Cisco often tests the distinction between a configuration that is accepted by the device (no commit errors) versus one that actually takes effect, trapping candidates who assume a successful commit means the policy is active.
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 device does not support the YANG model used
Cisco NSO uses YANG models to translate service definitions into device-specific CLI or NETCONF operations. If the target device does not support the YANG model referenced in the service package, the NETCONF or CLI operations will fail silently or produce no effect, as the device cannot interpret the configuration intent. This is a common validation failure when using model-driven orchestration with heterogeneous device populations.
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 device has a feature license missing for QoS
Why it's wrong here
Missing licenses typically generate clear error messages and would prevent the policy from being configured.
- ✓
The device does not support the YANG model used
Why this is correct
If the device lacks the required YANG modules, the configuration push may succeed but the policy may not be effective.
- ✓
The policy was applied to a subinterface but the YANG path specifies a main interface
Why this is correct
Applying the policy at the wrong interface hierarchy can result in it not being applied to the intended interface.
- ✓
The NETCONF transaction was not committed
Why this is correct
If the candidate configuration is not committed, the policy is not active on the device.
- ✗
The policy-map name conflicts with an existing one
Why it's wrong here
A name conflict would cause an error during push, making it obvious.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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