This LPIC-2 practice question tests your understanding of system security. 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.
An administrator wants to restrict SSH access to a server so that only users from the domain 'example.com' can connect. Which file and syntax should be used with TCP Wrappers?
Add to /etc/hosts.deny: sshd: ALL
Why wrong: Would deny all, not allow only example.com.
Add to /etc/hosts.allow: ALL: .example.com
Why wrong: Would allow all services from example.com, not just SSH.
Add to /etc/hosts.allow: sshd: .example.com
Allows SSH connections from example.com domain.
Add to /etc/hosts.allow: sshd: ALLOW .example.com
Why wrong: Invalid syntax; the keyword ALLOW is not used.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Add to /etc/hosts.allow: sshd: .example.com
Option C is correct because TCP Wrappers uses hosts.allow and hosts.deny. The syntax 'sshd: ALLOW .example.com' is incorrect; the correct syntax is 'sshd: .example.com' in hosts.allow. Option A is wrong because hosts.deny is for denying; but the question asks to allow only. Option B is wrong because the syntax is reversed. Option D is wrong because 'sshd: ALLOW .example.com' is not valid syntax.
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
For each option: why learners choose it and why it is or isn't the right answer here.
Add to /etc/hosts.deny: sshd: ALL
Why it's wrong here
Would deny all, not allow only example.com.
Add to /etc/hosts.allow: ALL: .example.com
Why it's wrong here
Would allow all services from example.com, not just SSH.
Add to /etc/hosts.allow: sshd: .example.com
Why this is correct
Allows SSH connections from example.com domain.
Related concept
Standard ACLs match source addresses.
Add to /etc/hosts.allow: sshd: ALLOW .example.com
Why it's wrong here
Invalid syntax; the keyword ALLOW is not used.
Common exam traps
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Trap categories for this question
Keyword trap
Invalid syntax; the keyword ALLOW is not used.
Detailed technical explanation
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.
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
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
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 LPIC-2 ACL questions on filtering logic and placement.
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FAQ
System Security — This question tests System Security — Standard ACLs match source addresses..
The correct answer is: Add to /etc/hosts.allow: sshd: .example.com — Option C is correct because TCP Wrappers uses hosts.allow and hosts.deny. The syntax 'sshd: ALLOW .example.com' is incorrect; the correct syntax is 'sshd: .example.com' in hosts.allow. Option A is wrong because hosts.deny is for denying; but the question asks to allow only. Option B is wrong because the syntax is reversed. Option D is wrong because 'sshd: ALLOW .example.com' is not valid syntax.
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 LPIC-2 ACL questions on filtering logic and placement.
Standard ACLs match source addresses.
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Last reviewed: Jun 24, 2026
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