LPIC-2 Advanced Networking Configuration Practice Question
This LPIC-2 practice question tests your understanding of advanced networking configuration. 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 is configuring netfilter rules to implement a stateful firewall. Which TWO of the following commands are necessary to allow the firewall to correctly forward TCP traffic from internal to external networks (assuming proper default policies)?
iptables -A FORWARD -m state --state NEW -j ACCEPT
Why wrong: This alone would allow all new connections without restriction, which is generally too permissive.
B
iptables -A FORWARD -m state --state ESTABLISHED -j ACCEPT
This allows established connections, crucial for stateful firewall.
C
iptables -A FORWARD -j ACCEPT
Why wrong: This would disable the firewall entirely.
D
iptables -A FORWARD -m state --state RELATED -j ACCEPT
This allows related traffic (e.g., FTP data), also necessary for stateful inspection.
E
iptables -A FORWARD -m state --state NEW -p tcp --dport 80 -j ACCEPT
Why wrong: This allows only HTTP new connections, but the question asks for necessary commands to forward TCP traffic in general; a rule for ESTABLISHED is essential.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
iptables -A FORWARD -m state --state ESTABLISHED -j ACCEPT
Option B is correct because a stateful firewall must allow packets belonging to already established connections to pass through the FORWARD chain. The `-m state --state ESTABLISHED` match ensures that any packet that is part of an existing TCP connection (i.e., has seen the three-way handshake) is accepted, which is essential for forwarding return traffic from external networks back to internal hosts.
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 FORWARD -m state --state NEW -j ACCEPT
Why it's wrong here
This alone would allow all new connections without restriction, which is generally too permissive.
✓
iptables -A FORWARD -m state --state ESTABLISHED -j ACCEPT
Why this is correct
This allows established connections, crucial for stateful firewall.
Related concept
Read the scenario before looking for a memorised answer.
iptables -A FORWARD -m state --state RELATED -j ACCEPT
Why this is correct
This allows related traffic (e.g., FTP data), also necessary for stateful inspection.
Related concept
Read the scenario before looking for a memorised answer.
✗
iptables -A FORWARD -m state --state NEW -p tcp --dport 80 -j ACCEPT
Why it's wrong here
This allows only HTTP new connections, but the question asks for necessary commands to forward TCP traffic in general; a rule for ESTABLISHED is essential.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think only the `ESTABLISHED` rule is needed, forgetting that `RELATED` is also required for protocols like FTP or ICMP error messages that are associated with an existing connection but are not part of the same TCP stream.
Trap categories for this question
Command / output trap
This allows only HTTP new connections, but the question asks for necessary commands to forward TCP traffic in general; a rule for ESTABLISHED is essential.
Detailed technical explanation
How to think about this question
The netfilter connection tracking system (`conntrack`) tracks the state of each network connection by inspecting packet headers and maintaining a state table. For TCP, the `ESTABLISHED` state is entered after the SYN/SYN-ACK/ACK handshake completes, and the `RELATED` state (option D) is used for ICMP errors or FTP data channels that are associated with an existing connection. In a typical stateful firewall configuration, you would also need a rule for `NEW` packets (e.g., `-m state --state NEW -p tcp --dport 80 -j ACCEPT`) to allow outbound HTTP connections, but the question specifically asks for rules necessary to forward TCP traffic, and the ESTABLISHED and RELATED rules are the core requirements for return traffic.
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 practitioner preparing for the LPIC-2 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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.
Advanced Networking Configuration — This question tests Advanced Networking Configuration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: iptables -A FORWARD -m state --state ESTABLISHED -j ACCEPT — Option B is correct because a stateful firewall must allow packets belonging to already established connections to pass through the FORWARD chain. The `-m state --state ESTABLISHED` match ensures that any packet that is part of an existing TCP connection (i.e., has seen the three-way handshake) is accepted, which is essential for forwarding return traffic from external networks back to internal hosts.
What should I do if I get this LPIC-2 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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