350-501 Automation and Assurance Practice Question
A network engineer at a service provider is using Cisco NSO to automate the provisioning of VLANs on thousands of access devices. The engineer creates a service using a custom YANG model and deploys it to a set of devices. However, the deployment fails with a 'failed to reach devices' error for some devices, while others succeed. The engineer checks device connectivity and confirms all devices are reachable via SSH and NETCONF. The engineer also verifies that the NSO device list is accurate and includes all target devices. What is the most likely cause of the failure?
⚠ Common exam trap
Cisco often tests the misconception that 'failed to reach devices' always indicates a network connectivity problem, when in fact it can be caused by NSO's synchronization check failing on a reachable device.
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 devices are not in sync with NSO.
When NSO deploys a service, it first checks whether the target devices are in sync with the NSO CDB (configuration database). If a device is out of sync (e.g., its running configuration differs from what NSO expects), NSO will refuse to push the new service configuration and will report a 'failed to reach devices' error, even though the device is reachable via SSH/NETCONF. This is a safety mechanism to prevent configuration conflicts or overwriting unmanaged changes.
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 service model uses an unsupported feature on those devices.
Why it's wrong here
An unsupported feature would result in a validation error, not a connectivity failure.
- ✓
The devices are not in sync with NSO.
Why this is correct
Out-of-sync devices prevent NSO from deploying services on them, and the error may manifest as 'failed to reach' because NSO cannot reconcile the configuration.
- ✗
The devices have insufficient memory to accept the configuration.
Why it's wrong here
Insufficient memory would cause a different error during configuration push, not a 'failed to reach' error.
- ✗
The NSO package is not loaded on those devices.
Why it's wrong here
NSO packages are loaded on the NSO server, not on the devices; this would not affect reachability.
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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.