This EX200 practice question tests your understanding of manage security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 administrator wants to allow user 'alice' to SSH into the server using key-based authentication only. Which configuration change is required?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add alice's public key to ~alice/.ssh/authorized_keys and set PubkeyAuthentication yes in sshd_config.
The correct approach is to add alice's public key to her authorized_keys file and ensure PubkeyAuthentication is enabled. Option A disables password auth for all, but doesn't enable key auth. Option C is for root. Option D places the private key incorrectly.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Add alice's public key to ~alice/.ssh/authorized_keys and set PubkeyAuthentication yes in sshd_config.
Why this is correct
This enables key-based authentication for alice.
Related concept
Standard ACLs match source addresses.
✗
Add alice's private key to /etc/ssh/authorized_keys.
Why it's wrong here
Private keys are never placed in authorized_keys.
✗
Set PasswordAuthentication no in /etc/ssh/sshd_config and restart sshd.
Why it's wrong here
This disables password auth but does not configure key-based auth.
✗
Set PermitRootLogin prohibit-password.
Why it's wrong here
This is specific to root, not a regular user.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related EX200 ACL questions on filtering logic and placement.
Manage security — This question tests Manage security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Add alice's public key to ~alice/.ssh/authorized_keys and set PubkeyAuthentication yes in sshd_config. — The correct approach is to add alice's public key to her authorized_keys file and ensure PubkeyAuthentication is enabled. Option A disables password auth for all, but doesn't enable key auth. Option C is for root. Option D places the private key incorrectly.
What should I do if I get this EX200 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related EX200 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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