This 200-901 practice question tests your understanding of network fundamentals. 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.
An automation script uses the Cisco IOS XE REST API to modify the running configuration. The script sends a PUT request to /restconf/data/Cisco-IOS-XE-native:native/interface/GigabitEthernet=1/0/1/ip/address. The response returns 405 Method Not Allowed. What is the most likely reason?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
PUT is not allowed on this resource; use PATCH instead.
The 405 Method Not Allowed response indicates that the HTTP method (PUT) is recognized but not supported for the specific resource. In RESTCONF, PUT is used for full resource replacement, but Cisco IOS XE often restricts PUT on certain configuration resources like interface IP addresses because they are nested leafs or lists that require partial updates. PATCH is the correct method for modifying specific fields without replacing the entire resource, aligning with RFC 8040 for partial resource modifications.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 request body is missing.
Why it's wrong here
Missing body would be 400.
✓
PUT is not allowed on this resource; use PATCH instead.
Why this is correct
RESTCONF often uses PATCH for partial updates; PUT might not be implemented.
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 interface does not exist.
Why it's wrong here
This would return 404.
✗
The script is not authenticated.
Why it's wrong here
Authentication issues return 401.
✗
The IP address format is incorrect.
Why it's wrong here
Format issues usually return 400.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between PUT and PATCH in RESTCONF, where candidates mistakenly assume PUT is always allowed for modifications, but the trap is that PUT requires full resource replacement and is often blocked on nested or list-based resources, making PATCH the correct choice for partial updates.
Detailed technical explanation
How to think about this question
RESTCONF (RFC 8040) defines PUT for creating or replacing a resource, but many YANG data models, including Cisco-IOS-XE-native, model IP addresses as child nodes under a list (e.g., primary/secondary). Replacing the entire 'address' container with PUT is often disallowed because it would require deleting and recreating the parent interface configuration. PATCH (using application/yang-data+xml or application/yang-data+json) allows partial updates to specific leafs without affecting sibling data, which is why it is the preferred method for modifying interface IP addresses in production automation scripts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Fundamentals — This question tests Network Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: PUT is not allowed on this resource; use PATCH instead. — The 405 Method Not Allowed response indicates that the HTTP method (PUT) is recognized but not supported for the specific resource. In RESTCONF, PUT is used for full resource replacement, but Cisco IOS XE often restricts PUT on certain configuration resources like interface IP addresses because they are nested leafs or lists that require partial updates. PATCH is the correct method for modifying specific fields without replacing the entire resource, aligning with RFC 8040 for partial resource modifications.
What should I do if I get this 200-901 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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