This 200-901 practice question tests your understanding of infrastructure and automation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 attempts to use RESTCONF to retrieve the running configuration of a Cisco IOS XE device. The GET request to '/restconf/data/Cisco-IOS-XE-native:native' returns a 405 Method Not Allowed error. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
The API key provided is invalid.
Why wrong: Invalid API key would give 401 or 403.
The request body was malformed.
Why wrong: GET requests don't have a body.
RESTCONF is not enabled or the YANG module is not supported.
RESTCONF must be enabled and the module accessible.
The device does not support HTTPS.
Why wrong: HTTPS support is required but 405 indicates method not allowed, not SSL.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
RESTCONF is not enabled or the YANG module is not supported.
A 405 Method Not Allowed error indicates that the HTTP method (GET) is not supported for the requested resource. In RESTCONF, this typically occurs when the RESTCONF service is not enabled on the device or the specific YANG module (Cisco-IOS-XE-native) is not supported or loaded. Without the service or module, the server cannot process the GET request for the running configuration.
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.
The API key provided is invalid.
Why it's wrong here
Invalid API key would give 401 or 403.
The request body was malformed.
Why it's wrong here
GET requests don't have a body.
RESTCONF is not enabled or the YANG module is not supported.
Why this is correct
RESTCONF must be enabled and the module accessible.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
The device does not support HTTPS.
Common exam traps
Cisco often tests the distinction between HTTP status codes (405 vs. 401 vs. 400) to see if candidates understand that 405 specifically relates to an unsupported HTTP method or disabled service, not authentication or malformed data.
Detailed technical explanation
RESTCONF (RFC 8040) relies on the NETCONF YANG modules being loaded and the RESTCONF service being explicitly enabled (e.g., via 'restconf' under the 'ip http server' or 'ip http secure-server' configuration on IOS XE). The 405 error can also occur if the YANG module defines the resource as a 'list' or 'container' that does not support direct GET operations without specifying a key, but in this case, the most common cause is the service or module not being available.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Infrastructure and Automation — This question tests Infrastructure and Automation — Read the scenario before looking for a memorised answer..
The correct answer is: RESTCONF is not enabled or the YANG module is not supported. — A 405 Method Not Allowed error indicates that the HTTP method (GET) is not supported for the requested resource. In RESTCONF, this typically occurs when the RESTCONF service is not enabled on the device or the specific YANG module (Cisco-IOS-XE-native) is not supported or loaded. Without the service or module, the server cannot process the GET request for the running configuration.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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