200-901 Cisco Platforms and Development Practice Question
This 200-901 practice question tests your understanding of cisco platforms and development. 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.
An Ansible playbook using the ios_config module fails with the error 'unable to open connection'. The network device is reachable via SSH from the Ansible control node. What is the most likely cause?
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 SSH key exchange algorithm is not supported by the device
The error 'unable to open connection' indicates that Ansible cannot establish an SSH session with the device, even though the device is reachable. Since the device is reachable via SSH from the control node, the most likely cause is a mismatch in SSH key exchange algorithms, where the device only supports older algorithms (e.g., diffie-hellman-group1-sha1) that are not enabled by default in modern SSH clients. This is a common issue when connecting to legacy Cisco IOS devices that lack updated SSH configurations.
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 device has an invalid username and password
Why it's wrong here
Invalid credentials would produce an authentication error.
✗
The Ansible user does not have privilege level 15 on the device
Why it's wrong here
Privilege level affects configuration, not connection establishment.
✓
The SSH key exchange algorithm is not supported by the device
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between SSH transport errors (key exchange, ciphers) and authentication/authorization errors, leading candidates to incorrectly blame credentials or privilege levels when the actual issue is a cryptographic algorithm mismatch.
Detailed technical explanation
How to think about this question
SSH key exchange algorithms are negotiated during the initial handshake before any authentication occurs. Cisco IOS devices often default to older algorithms like diffie-hellman-group1-sha1 (RFC 4253) or diffie-hellman-group14-sha1, which are disabled in OpenSSH 7.0+ due to security concerns. This mismatch causes the SSH transport layer to fail immediately, resulting in 'unable to open connection' even though the device is IP-reachable. The fix involves either enabling legacy algorithms on the Ansible control node via ssh_args or updating the device to support modern algorithms.
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
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.
Cisco Platforms and Development — This question tests Cisco Platforms and Development — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The SSH key exchange algorithm is not supported by the device — The error 'unable to open connection' indicates that Ansible cannot establish an SSH session with the device, even though the device is reachable. Since the device is reachable via SSH from the control node, the most likely cause is a mismatch in SSH key exchange algorithms, where the device only supports older algorithms (e.g., diffie-hellman-group1-sha1) that are not enabled by default in modern SSH clients. This is a common issue when connecting to legacy Cisco IOS devices that lack updated SSH configurations.
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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