This 350-401 practice question tests your understanding of 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 is creating a Python script using the Cisco IOS XE RESTCONF API to configure a loopback interface. The script sends a PUT request to the URI /restconf/data/Cisco-IOS-XE-native:native/interface/Loopback=100 with a JSON body that includes the IP address. The API returns a 201 Created status, but the loopback interface does not appear in the running configuration. What is the most likely issue?
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 PUT request should be a POST request to create a new resource
D is correct because RESTCONF uses PUT to create or replace a resource only when the client specifies the entire resource URI, including the resource identifier (e.g., Loopback=100). However, for a new resource, the API may require a POST to the parent collection (e.g., /restconf/data/Cisco-IOS-XE-native:native/interface/Loopback) to trigger creation, depending on the YANG module's data model. A 201 Created response indicates the request was accepted, but if the resource was not actually created in the running configuration, it suggests the PUT was treated as a no-op or the data was not applied due to a mismatch in the expected resource state.
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 RESTCONF API returned an error but the script ignored it
Why it's wrong here
201 Created indicates success.
✗
The loopback interface number is incorrect in the URI
Why it's wrong here
The URI syntax is correct.
✗
The script is not authenticated properly
Why it's wrong here
Authentication errors would return 401 or 403.
✓
The PUT request should be a POST request to create a new resource
Why this is correct
POST is used to create a new resource; PUT replaces an existing one.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between PUT and POST in RESTCONF, where candidates mistakenly assume PUT always creates a new resource, but the correct behavior depends on the YANG module's definition and whether the resource identifier is part of the URI or the payload.
Detailed technical explanation
How to think about this question
RESTCONF (RFC 8040) defines PUT as a full resource replacement operation that requires the resource to already exist or be explicitly created by the server if the YANG data model supports 'create-on-put'. In Cisco IOS XE, the native YANG model for Loopback interfaces often requires a POST to the collection to instantiate a new interface, as PUT may only update existing entries. A 201 Created response can be misleading if the server acknowledges the request but the data is not committed to the running configuration due to validation or transactional constraints.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
Automation — This question tests Automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The PUT request should be a POST request to create a new resource — D is correct because RESTCONF uses PUT to create or replace a resource only when the client specifies the entire resource URI, including the resource identifier (e.g., Loopback=100). However, for a new resource, the API may require a POST to the parent collection (e.g., /restconf/data/Cisco-IOS-XE-native:native/interface/Loopback) to trigger creation, depending on the YANG module's data model. A 201 Created response indicates the request was accepted, but if the resource was not actually created in the running configuration, it suggests the PUT was treated as a no-op or the data was not applied due to a mismatch in the expected resource state.
What should I do if I get this 350-401 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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