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200-901 Practice Question: You manage a network that uses a mix of Cisco IOS…
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?
⚠ Common exam trap
Cisco often tests the distinction between read-only and read-write RESTCONF configurations, where candidates assume a successful GET implies full functionality, but write operations require explicit enablement.
Answer choices
Why each option matters
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.
The 405 Method Not Allowed error indicates that the RESTCONF service on the router is not enabled for write operations. By default, RESTCONF on IOS-XE devices may be configured in read-only mode, or the necessary HTTP methods (PATCH, PUT, POST) are not permitted. Since the GET request succeeds but PATCH fails, the service is operational but write access is restricted, often due to missing 'ip http secure-server' or 'restconf' configuration with write permissions.
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.
- ✗
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.
Why it's wrong here
Basic auth works for all HTTP methods.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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