200-901 Infrastructure and Automation Practice Question
This 200-901 practice question tests your understanding of infrastructure and 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 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?
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 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.
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 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.
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 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.
Detailed technical explanation
How to think about this question
NETCONF over SSH (RFC 6242) uses SSH as the transport layer; the ncclient library first establishes an SSH connection and then performs NETCONF capability exchange. If the SSH server on the device is configured to require public key authentication (e.g., via 'ip ssh pubkey-chain' or AAA authentication), password authentication will fail at the SSH layer, raising an AuthenticationError. This is distinct from NETCONF-level errors, which occur after SSH authentication succeeds.
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 practitioner preparing for the 200-901 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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.
Infrastructure and Automation — This question tests Infrastructure and Automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
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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