Question 539 of 989
200-901 Infrastructure and Automation Practice Question
A network automation engineer is developing a Python script that uses the NETCONF protocol to retrieve the running configuration from a Cisco IOS XE device. They use the ncclient library. The script works on the test device but fails on a production device with an error: "ncclient.transport.errors.AuthenticationError: Authentication exception". The engineer verifies that the SSH credentials (username and password) are correct and that the production device is reachable via SSH on port 830. What is the most likely issue?
⚠ Common exam trap
Cisco often tests the distinction between SSH transport authentication failures and NETCONF protocol-level failures, leading candidates to incorrectly attribute the error to NETCONF not being enabled or a firewall issue rather than the SSH authentication method mismatch.
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 production device requires SSH key-based authentication, but the script uses password.
The error 'AuthenticationException' from ncclient indicates that the NETCONF session over SSH failed during authentication. Since the engineer verified the password is correct and the device is reachable on port 830, the most likely cause is that the production device is configured to require SSH key-based authentication (e.g., using 'ip ssh server algorithm authentication publickey' or similar), while the script is attempting password-based authentication. ncclient defaults to password authentication unless explicitly configured with a key filename.
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 production device uses a different port for NETCONF than the test device.
Why it's wrong here
If port were different, the connection would fail at the TCP level, not with an authentication error.
- ✗
The production device has a firewall rule blocking NETCONF capabilities.
Why it's wrong here
Firewall blocking would cause connection timeouts or resets, not authentication errors.
- ✗
The production device does not have NETCONF enabled; it only supports SSH.
Why it's wrong here
If NETCONF were disabled, ncclient would raise a different error (e.g., 'no NETCONF capability').
- ✓
The production device requires SSH key-based authentication, but the script uses password.
Why this is correct
Many production devices require keys for NETCONF authentication; password may fail at the NETCONF layer.
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Last reviewed: Jun 24, 2026
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