This XK0-005 practice question tests your understanding of system management. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 Linux administrator is configuring secure remote access to a server. Which three of the following are recommended best practices for securing SSH? (Choose three.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable public key authentication.
Disabling root login (PermitRootLogin no), using public key authentication (PubkeyAuthentication yes), and restricting allowed users/groups (AllowUsers or AllowGroups) are common best practices. Changing the default port (Port 2222) is optional and considered security through obscurity, not a true security measure. Password authentication is less secure than key-based.
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.
✓
Enable public key authentication.
Why this is correct
Key-based authentication is more secure than passwords.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
Use password authentication only.
Why it's wrong here
Passwords are vulnerable to brute-force; key-based is recommended.
✓
Disable root login via SSH.
Why this is correct
Prevents direct root login; users must sudo.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
Change the default SSH port to a non-standard port.
Why it's wrong here
Security through obscurity; not a true best practice.
✓
Allow only specific users or groups.
Why this is correct
Limiting access reduces attack surface.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
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 XK0-005 ACL questions on filtering logic and placement.
System Management — This question tests System Management — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Enable public key authentication. — Disabling root login (PermitRootLogin no), using public key authentication (PubkeyAuthentication yes), and restricting allowed users/groups (AllowUsers or AllowGroups) are common best practices. Changing the default port (Port 2222) is optional and considered security through obscurity, not a true security measure. Password authentication is less secure than key-based.
What should I do if I get this XK0-005 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 XK0-005 ACL questions on filtering logic and placement.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Standard ACLs match source addresses.
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