The correct answer is `iptables -A INPUT -p tcp --dport 3306 -s 192.168.1.0/24 -j ACCEPT`. This rule works by appending a filter to the INPUT chain that matches TCP packets destined for port 3306, but only if their source IP address falls within the 192.168.1.0/24 subnet, explicitly accepting those connections while all other traffic is implicitly denied by the default policy or subsequent drop rules. On the LPIC-1 exam, this tests your understanding of stateful packet filtering and the critical order of iptables rules—a common trap is forgetting the `-s` flag or placing the rule after a blanket DROP, which would block the intended traffic. Remember the mnemonic "Source, Service, then Accept": always specify the source subnet first, then the service port, and finally the accept target to ensure only trusted networks reach sensitive services like MySQL.
LPIC-1 Essential System Services and Networking Practice Question
This LPIC-1 practice question tests your understanding of essential system services and networking. 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.
A database server on a Linux system is configured to listen on TCP port 3306. The administrator wants to restrict access to the database server to only the local network (192.168.1.0/24) using iptables. Which of the following iptables rules achieves this?
Option C is correct because it adds an INPUT chain rule that accepts TCP traffic destined for port 3306 only when the source address is within the 192.168.1.0/24 subnet. This effectively restricts incoming database connections to the local network, while all other sources are implicitly dropped by the default INPUT policy or subsequent rules.
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.
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iptables -A INPUT -p tcp --dport 3306 -d 192.168.1.0/24 -j DROP
OUTPUT chain and source port incorrect for inbound restriction.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing the -s (source) and -d (destination) flags, leading candidates to pick Option A which drops traffic to the local network instead of accepting traffic from it.
Trap categories for this question
Command / output trap
OUTPUT chain affects outbound, not inbound.
Detailed technical explanation
How to think about this question
iptables processes packets through chain traversal: for incoming packets, the INPUT chain is evaluated after routing. The -s flag matches the source IP, which is critical for access control based on where the connection originates. A common real-world scenario is a MySQL server (default port 3306) that should only accept connections from application servers on the same subnet; using -s 192.168.1.0/24 with ACCEPT ensures that, while a final DROP rule or default policy handles all other sources.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Essential System Services and Networking — This question tests Essential System Services and Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: iptables -A INPUT -p tcp --dport 3306 -s 192.168.1.0/24 -j ACCEPT — Option C is correct because it adds an INPUT chain rule that accepts TCP traffic destined for port 3306 only when the source address is within the 192.168.1.0/24 subnet. This effectively restricts incoming database connections to the local network, while all other sources are implicitly dropped by the default INPUT policy or subsequent rules.
What should I do if I get this LPIC-1 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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