200-901 Infrastructure and Automation Practice Question
You are a network automation engineer at a large enterprise. The network consists of 200 Cisco Catalyst switches distributed across five data centers. Each switch runs IOS-XE and supports NETCONF. Your team uses a centralized Ansible control node to manage configurations. Recently, the security team mandated that all management access must use SSH keys instead of passwords. You updated the Ansible inventory to use SSH keys and tested on a few switches successfully. However, when you run the playbook against all switches, about 30 switches fail with the error: 'Authentication failed.' You verify that the SSH public key is correctly deployed on those switches via the console. What is the most likely cause of the failure?
⚠ Common exam trap
Cisco often tests the subtle distinction between SSH key format issues and file permission issues, where candidates assume the problem is key format when the real issue is the private key file's restrictive permissions required by OpenSSH.
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 private key file on the Ansible control node has permissions 644, which SSH rejects
SSH strictly requires private key files to have permissions no more permissive than 600 (owner read/write) or 640 (owner read/write, group read) on Unix-like systems. A permission of 644 allows group and others to read the key, which SSH interprets as insecure and refuses to use, causing 'Authentication failed' even though the public key is correctly deployed on the switches.
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 public key on the switches is not in the correct format
Why it's wrong here
The engineer verified the public key is correct via console.
- ✗
The Ansible become method is misconfigured
Why it's wrong here
Become is for privilege escalation, not SSH login.
- ✓
The private key file on the Ansible control node has permissions 644, which SSH rejects
Why this is correct
SSH requires private key permissions to be 600 or more restrictive.
- ✗
The switches are not reachable over the network
Why it's wrong here
The error is authentication, not connectivity.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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