This LPIC-2 practice question tests your understanding of system security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Network Topology
Refer to the exhibit. An administrator has applied these iptables rules. Users can still SSH into the server from any IP address, which is unexpected because the administrator intended to restrict SSH to only a specific subnet. What is the most likely reason the restriction is not working?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SSH rule does not specify a source IP, so it accepts connections from any IP.
Option C is correct because the default policy ACCEPT allows all traffic that is not matched by explicit rules, but the last rule DROP should drop everything. However, the rule allowing SSH accepts from any source (no -s option). So actually it is working as configured: SSH is allowed from all sources. So the administrator forgot to add a source specification. That is the issue. Option A is wrong because conntrack is fine. Option B is wrong because the rules are in order. Option D is wrong because the drop rule is present but it only drops after allowed. The correct answer is that the SSH rule does not restrict source, so all IPs are allowed.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 SSH rule does not specify a source IP, so it accepts connections from any IP.
Why this is correct
Without a -s option, the rule matches all source IPs, leading to unrestricted SSH access.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The default policy is ACCEPT, so the DROP rule is ignored.
Why it's wrong here
The DROP rule is explicit and overrides the default policy for matched packets.
✗
The conntrack module is not loaded, so the state matching fails.
Why it's wrong here
If conntrack were not loaded, the rules would fail entirely; SSH would not work at all.
✗
The rules are in the wrong order; the DROP rule should be before the SSH rule.
Why it's wrong here
Order is correct: established/related first, then new SSH, then drop.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related LPIC-2 subnetting questions on CIDR, address ranges, and subnet selection.
System Security — This question tests System Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The SSH rule does not specify a source IP, so it accepts connections from any IP. — Option C is correct because the default policy ACCEPT allows all traffic that is not matched by explicit rules, but the last rule DROP should drop everything. However, the rule allowing SSH accepts from any source (no -s option). So actually it is working as configured: SSH is allowed from all sources. So the administrator forgot to add a source specification. That is the issue. Option A is wrong because conntrack is fine. Option B is wrong because the rules are in order. Option D is wrong because the drop rule is present but it only drops after allowed. The correct answer is that the SSH rule does not restrict source, so all IPs are allowed.
What should I do if I get this LPIC-2 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related LPIC-2 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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