The answer is to add a DNAT rule in the PREROUTING chain of the nat table to translate destination 203.0.113.10:80 to 192.168.1.100:80. This is correct because while the existing MASQUERADE rule handles source NAT for outbound traffic, it does not alter the destination of incoming packets; DNAT in PREROUTING rewrites the destination IP and port before the routing decision, allowing external packets to be forwarded to the internal web server. On the LPIC-2 exam, this scenario tests your understanding of the separation between SNAT and DNAT within the nat table’s chains, a common trap being that students confuse PREROUTING (for DNAT) with POSTROUTING (for SNAT). Remember the flow: PREROUTING changes where packets go, POSTROUTING changes where they came from. A useful memory tip is “PREROUTING for the destination, POSTROUTING for the source.”
LPIC-2 Advanced Networking Configuration Practice Question
This LPIC-2 practice question tests your understanding of advanced networking configuration. 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.
A company has a Linux server with two network interfaces: eth0 connected to the internal 192.168.1.0/24 network, and eth1 connected to the internet via a public IP of 203.0.113.10. The server runs a web server on port 80 and needs to allow internal clients to access the internet while hiding their private IPs (MASQUERADE). Additionally, external users should be able to reach the web server using the public IP. The administrator has enabled IP forwarding and configured iptables with the following rules:
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE
iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT
However, internal clients can access the internet, but external users cannot reach the web server. What should the administrator do to fix the issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a DNAT rule in the PREROUTING chain of the nat table to translate destination 203.0.113.10:80 to 192.168.1.100:80.
The current iptables rules perform SNAT/MASQUERADE for outbound traffic and allow forwarding of related/established inbound traffic, but they do not redirect incoming connections destined for the public IP (203.0.113.10:80) to the internal web server (e.g., 192.168.1.100:80). A DNAT rule in the PREROUTING chain of the nat table is required to translate the destination address and port, so that external packets are forwarded to the internal server and the response traffic is handled by the existing MASQUERADE rule.
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.
✓
Add a DNAT rule in the PREROUTING chain of the nat table to translate destination 203.0.113.10:80 to 192.168.1.100:80.
Why this is correct
This will redirect incoming packets to the internal web server.
Related concept
Read the scenario before looking for a memorised answer.
✗
Add a FORWARD rule to allow new connections from eth1 to eth0.
Why it's wrong here
The FORWARD rules already allow related/established; a DNAT is needed for new connections.
✗
Add a rule in the INPUT chain to accept traffic on port 80.
Why it's wrong here
INPUT chain handles traffic destined to the server itself, not forwarded traffic.
✗
Change the MASQUERADE rule to SNAT with the public IP.
Why it's wrong here
MASQUERADE is fine for outbound traffic; the issue is inbound.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the need for DNAT with simply opening firewall rules (INPUT or FORWARD), forgetting that without destination address translation, the internal server never sees the packet as destined for itself.
Detailed technical explanation
How to think about this question
DNAT in the PREROUTING chain modifies the destination IP/port before the routing decision, allowing external packets to be redirected to an internal server. The conntrack system tracks the translation so that reply packets are automatically un-DNATed (reverse translation) before being sent back to the external client. In a real-world scenario, if the web server were on a different subnet, a static route might also be needed to ensure return traffic reaches the firewall.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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: Add a DNAT rule in the PREROUTING chain of the nat table to translate destination 203.0.113.10:80 to 192.168.1.100:80. — The current iptables rules perform SNAT/MASQUERADE for outbound traffic and allow forwarding of related/established inbound traffic, but they do not redirect incoming connections destined for the public IP (203.0.113.10:80) to the internal web server (e.g., 192.168.1.100:80). A DNAT rule in the PREROUTING chain of the nat table is required to translate the destination address and port, so that external packets are forwarded to the internal server and the response traffic is handled by the existing MASQUERADE rule.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This LPIC-2 practice question is part of Courseiva's free LPI certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LPIC-2 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.