This 200-901 practice question tests your understanding of cisco platforms and development. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 network engineer needs to automate the configuration of VLANs on a set of Cisco switches using Ansible. Which API should be targeted to ensure idempotent configuration updates?
NETCONF/YANG
NETCONF/YANG supports idempotent operations through data model validation and transaction support.
REST API of Cisco DNA Center
Why wrong: DNA Center REST API is for higher-level intent, not for direct switch configuration.
SNMP
Why wrong: SNMP is not idempotent and can cause unintended side effects.
CLI with SSH
Why wrong: CLI is imperative and not idempotent; repeated commands may cause errors.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
NETCONF/YANG
NETCONF/YANG is the correct choice because NETCONF provides a transactional, lock-based mechanism that ensures idempotent configuration updates—applying the desired state exactly once without side effects from repeated runs. YANG models define the VLAN configuration structure, allowing Ansible to compare the current device state against the desired state and only push changes when necessary, which is the essence of idempotency.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
NETCONF/YANG
Why this is correct
NETCONF/YANG supports idempotent operations through data model validation and transaction support.
Related concept
Read the scenario before looking for a memorised answer.
REST API of Cisco DNA Center
Why it's wrong here
DNA Center REST API is for higher-level intent, not for direct switch configuration.
SNMP
Why it's wrong here
SNMP is not idempotent and can cause unintended side effects.
CLI with SSH
Why it's wrong here
CLI is imperative and not idempotent; repeated commands may cause errors.
Common exam traps
Cisco often tests the misconception that CLI with SSH is sufficient for automation, but the trap here is that CLI commands are not idempotent by default—candidates overlook the need for a structured, transactional protocol like NETCONF to guarantee repeatable, safe configuration updates.
Trap categories for this question
Command / output trap
CLI is imperative and not idempotent; repeated commands may cause errors.
Detailed technical explanation
NETCONF uses the <edit-config> operation with the 'merge' or 'replace' option to achieve idempotency, and YANG models like 'Cisco-IOS-XE-vlan' define the exact schema for VLAN objects. Under the hood, NETCONF sessions use a candidate configuration datastore that can be validated and committed atomically, ensuring that repeated Ansible playbook runs do not create duplicate VLANs or cause configuration drift. In a real-world scenario, a network engineer automating VLAN provisioning across hundreds of switches can safely re-run the same playbook during maintenance windows without fear of unintended side effects.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
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FAQ
Cisco Platforms and Development — This question tests Cisco Platforms and Development — Read the scenario before looking for a memorised answer..
The correct answer is: NETCONF/YANG — NETCONF/YANG is the correct choice because NETCONF provides a transactional, lock-based mechanism that ensures idempotent configuration updates—applying the desired state exactly once without side effects from repeated runs. YANG models define the VLAN configuration structure, allowing Ansible to compare the current device state against the desired state and only push changes when necessary, which is the essence of idempotency.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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