- A
iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP
Why wrong: This allows only established connections, not new HTTPS connections.
- B
iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -P INPUT ACCEPT
Why wrong: This accepts all incoming traffic, not just HTTPS.
- C
iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP; iptables -P OUTPUT ACCEPT
This allows incoming HTTPS, blocks other inbound, and allows all outbound.
- D
iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP; iptables -P OUTPUT DROP
Why wrong: This blocks all outgoing traffic, preventing the database connection.
Quick Answer
The answer is Option C, which uses `iptables -A INPUT -p tcp --dport 443 -j ACCEPT` to allow HTTPS, `iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT` for return traffic, and `iptables -P INPUT DROP` to block everything else. This configuration is correct because it implements an iptables default DROP policy while selectively allowing specific ports, ensuring the web server on 192.168.1.10 is reachable on port 443 from the internet, while the ESTABLISHED,RELATED rule permits the server’s outbound communication to the internal database on port 3306 without needing an explicit inbound rule for that port. On the LFCS exam, this scenario tests your understanding of stateful firewall rules and the critical order of operations: you must add ACCEPT rules before setting the default DROP policy, or all traffic will be blocked. A common trap is forgetting the ESTABLISHED,RELATED rule, which would break return traffic for the database connection. Memory tip: think “Allow first, then drop—state keeps the conversation flowing.”
LFCS Networking Practice Question
This LFCS practice question tests your understanding of networking. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 company wants to ensure that a web server (IP 192.168.1.10) is accessible from the internet via port 443, but all other inbound traffic should be blocked. The server also needs to communicate with an internal database (IP 10.0.0.50) on port 3306. The default firewall zone is 'public'. Which iptables rules should be applied to the server?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP; iptables -P OUTPUT ACCEPT
Option C is correct because it explicitly allows inbound HTTPS traffic on port 443, permits return traffic for established/related connections (which is essential for the server to communicate with the internal database on port 3306), and sets a default DROP policy on the INPUT chain to block all other inbound traffic. The OUTPUT chain is left with a default ACCEPT policy, allowing the server to initiate outbound connections to the database without additional 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.
- ✗
iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP
Why it's wrong here
This allows only established connections, not new HTTPS connections.
- ✗
iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -P INPUT ACCEPT
Why it's wrong here
This accepts all incoming traffic, not just HTTPS.
- ✓
iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP; iptables -P OUTPUT ACCEPT
Why this is correct
This allows incoming HTTPS, blocks other inbound, and allows all outbound.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP; iptables -P OUTPUT DROP
Why it's wrong here
This blocks all outgoing traffic, preventing the database connection.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often forget to set a default DROP policy on the INPUT chain or mistakenly set a default DROP on the OUTPUT chain, thinking it enhances security, but this breaks outbound connectivity required for the server to communicate with the internal database.
Detailed technical explanation
How to think about this question
The iptables connection tracking system (conntrack) uses the ESTABLISHED and RELATED states to automatically permit return packets for connections initiated by the server (e.g., to the database on port 3306) without requiring explicit rules for each destination. The default policy on the INPUT chain (DROP) ensures that any packet not matching an explicit ACCEPT rule is discarded, providing a whitelist-only security model. In a real-world scenario, the server would also need a rule to allow loopback traffic (e.g., -A INPUT -i lo -j ACCEPT) to prevent local services from being blocked, though this is not explicitly tested here.
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.
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FAQ
Questions learners often ask
What does this LFCS question test?
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: iptables -A INPUT -p tcp --dport 443 -j ACCEPT; iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT; iptables -P INPUT DROP; iptables -P OUTPUT ACCEPT — Option C is correct because it explicitly allows inbound HTTPS traffic on port 443, permits return traffic for established/related connections (which is essential for the server to communicate with the internal database on port 3306), and sets a default DROP policy on the INPUT chain to block all other inbound traffic. The OUTPUT chain is left with a default ACCEPT policy, allowing the server to initiate outbound connections to the database without additional rules.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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