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.
You manage a network that uses a mix of Cisco IOS and IOS-XE devices. The company wants to implement network automation using RESTCONF and YANG. You have configured RESTCONF on a branch router running IOS-XE 16.12. You can successfully retrieve the interface configuration using a GET request from a Python script. However, when you try to modify the description of an interface using a PATCH request, you receive a 405 Method Not Allowed error. The script uses basic authentication over HTTPS. The URL is correct, and the YANG data payload is valid. What is the most likely reason for the failure?
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
✓
The RESTCONF service on the router is not enabled for write operations.
RESTCONF on IOS-XE may require specific HTTP methods to be enabled. By default, only GET is allowed; PATCH and PUT require explicit configuration or the 'restconf' capability advertisement. Option A is correct because the router may not have the 'restconf' capability with write support. Option B is wrong because basic authentication is supported. Option C is wrong because the URL is for the interface, not the whole configuration. Option D is wrong because YANG is valid.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 RESTCONF service on the router is not enabled for write operations.
Why this is correct
The 'restconf' capability may be read-only; you need to enable the 'restconf' agent with write support.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The YANG payload must be in XML format instead of JSON.
Why it's wrong here
Both XML and JSON are supported; the error is 405, not 400.
✗
Basic authentication is not supported for PATCH requests.
The PATCH request must target the entire configuration data store, not a specific interface.
Why it's wrong here
PATCH can target a specific resource like an interface.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-901 NAT questions on configuration and troubleshooting.
Network Fundamentals — This question tests Network Fundamentals — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The RESTCONF service on the router is not enabled for write operations. — RESTCONF on IOS-XE may require specific HTTP methods to be enabled. By default, only GET is allowed; PATCH and PUT require explicit configuration or the 'restconf' capability advertisement. Option A is correct because the router may not have the 'restconf' capability with write support. Option B is wrong because basic authentication is supported. Option C is wrong because the URL is for the interface, not the whole configuration. Option D is wrong because YANG is valid.
What should I do if I get this 200-901 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-901 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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