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200-901 Practice Question: An Ansible playbook using the ios_config module…
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?
⚠ Common exam trap
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.
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 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.
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
Why this is correct
Unsupported key exchange algorithm causes SSH connection failure.
- ✗
The ios_config module requires NETCONF instead of SSH
Why it's wrong here
ios_config uses SSH by default, not NETCONF.
Quick reference
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-901 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-901 exam.