The correct answer is that the SSH rule only allows connections from the 10.0.1.0/24 subnet, and the remote host at 192.168.1.100 is not within that range. This happens because iptables processes rules sequentially; when an SSH packet arrives, it checks the source IP against the explicit ACCEPT rule for port 22, which is restricted to the 10.0.1.0/24 network. Since 192.168.1.100 does not match, the packet falls through to the default policy, which, even if set to ACCEPT, does not override the more specific source restriction—the SSH service remains blocked by iptables source restriction. On the LFCS exam, this scenario tests your understanding of how iptables rule ordering and subnet matching override a global ACCEPT policy, a common trap where candidates assume a permissive default policy allows all traffic. Remember the key tip: a specific source restriction on a service rule always takes precedence over a general ACCEPT policy, so always check the source subnet before the default action.
LFCS Networking Practice Question
This LFCS practice question tests your understanding of networking. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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
An administrator is unable to SSH into the server from a remote host at 192.168.1.100. Based on the exhibited iptables rules, what is the most likely reason?
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 only allows connections from 10.0.1.0/24, and 192.168.1.100 is not in that subnet
Option A is correct because the exhibited iptables rules show an SSH rule that explicitly accepts incoming TCP traffic on port 22 only from the source subnet 10.0.1.0/24. The remote host at 192.168.1.100 is not within that subnet, so the SSH rule does not match, and the packet will fall through to the next rule or the default policy. Since no other rule permits SSH from 192.168.1.100, the connection is implicitly dropped or rejected, preventing SSH access.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 only allows connections from 10.0.1.0/24, and 192.168.1.100 is not in that subnet
Why this is correct
The second rule allows SSH only from 10.0.1.0/24, and the third rule drops all other SSH.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
The INPUT chain policy is ACCEPT, so SSH should be allowed
Why it's wrong here
The explicit DROP rule overrides the default policy.
✗
The DROP rule for SSH is not matching because of packet count zero
Why it's wrong here
The packet count is zero because no packets have matched yet; it will match if traffic arrives.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates see the INPUT chain policy is ACCEPT and assume all traffic is allowed, overlooking that a more specific rule (like the SSH rule with a source restriction) can prevent traffic from non-matching sources, effectively overriding the default policy for that service.
Detailed technical explanation
How to think about this question
In iptables, rules are evaluated in order, and the first matching rule determines the packet's fate (e.g., ACCEPT, DROP). The SSH rule here uses the `-s` flag to specify a source IP range, which is a standard netfilter match; packets from outside that range skip the rule and continue to the next. The default policy (ACCEPT) only applies if no rule matches, but because the SSH rule is present and does not match, the packet is not explicitly accepted—it will be processed by subsequent rules, which may drop it or let it pass. In practice, administrators often place restrictive rules before permissive ones, and a common mistake is assuming a default ACCEPT policy allows all traffic, ignoring that earlier rules can block it.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The SSH rule only allows connections from 10.0.1.0/24, and 192.168.1.100 is not in that subnet — Option A is correct because the exhibited iptables rules show an SSH rule that explicitly accepts incoming TCP traffic on port 22 only from the source subnet 10.0.1.0/24. The remote host at 192.168.1.100 is not within that subnet, so the SSH rule does not match, and the packet will fall through to the next rule or the default policy. Since no other rule permits SSH from 192.168.1.100, the connection is implicitly dropped or rejected, preventing SSH access.
What should I do if I get this LFCS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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Question Discussion
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