The answer is that the TCP SYN packet is forwarded to 10.0.2.5:80 via eth1 with the source IP unchanged. This occurs because the router applies a Destination NAT (DNAT) rule that rewrites the packet’s destination IP and port from 10.0.1.10:8080 to the internal server’s address, while leaving the source address untouched—DNAT only modifies the destination, not the origin. On the LPIC-2 exam, this scenario tests your understanding of stateless NAT behavior in a port forwarding context; a common trap is assuming the source IP is also translated, which would require Source NAT (SNAT) or masquerading. Remember that DNAT is a one-way street: it changes where the packet is going, not where it came from. For the exam, keep this memory tip in mind: “DNAT changes the ‘to,’ not the ‘from’.”
LPIC-2 Advanced Networking Configuration Practice Question
This LPIC-2 practice question tests your understanding of advanced networking configuration. 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.
Network Topology
A client on the internet sends a TCP SYN packet to 10.0.1.10:8080. The router receives it on eth0. According to the exhibit, what will happen to the packet?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The packet is forwarded to 10.0.2.5:80 via eth1, with source IP unchanged.
The router receives the TCP SYN packet on eth0 destined for 10.0.1.10:8080. According to the exhibit (not shown but implied), a destination NAT (DNAT) rule is configured to translate the destination IP and port to 10.0.2.5:80. The packet is forwarded out eth1 with the destination changed, but the source IP remains unchanged because DNAT does not modify the source address. This is a standard port forwarding scenario.
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 packet is dropped because the destination IP is not directly connected.
Why it's wrong here
DNAT changes the destination to a directly connected network (10.0.2.0/24).
✗
The packet is forwarded to 10.0.1.1 because it is the default gateway.
Why it's wrong here
After DNAT, the destination is 10.0.2.5, so routing will send it to that network, not the default gateway.
✗
The packet is forwarded to 10.0.2.5:80 via eth1, with source IP changed to 10.0.2.20.
Why it's wrong here
MASQUERADE would only change source if the packet originated from 10.0.2.0/24.
✓
The packet is forwarded to 10.0.2.5:80 via eth1, with source IP unchanged.
Why this is correct
As described, DNAT changes destination, routing sends it to eth1, and no SNAT is applied.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse DNAT with SNAT and assume the source IP is also changed, or they think the packet is dropped because the destination IP is not directly connected to the router's LAN interface.
Detailed technical explanation
How to think about this question
Destination NAT (DNAT) is typically implemented using iptables rules (e.g., `-j DNAT --to-destination 10.0.2.5:80`) in the PREROUTING chain of the nat table. The router performs the translation before the routing decision, so the packet is routed based on the new destination. The source IP remains the original client IP, which allows the internal server to see the real client address, but return traffic must be routed back through the same router to un-NAT correctly.
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: The packet is forwarded to 10.0.2.5:80 via eth1, with source IP unchanged. — The router receives the TCP SYN packet on eth0 destined for 10.0.1.10:8080. According to the exhibit (not shown but implied), a destination NAT (DNAT) rule is configured to translate the destination IP and port to 10.0.2.5:80. The packet is forwarded out eth1 with the destination changed, but the source IP remains unchanged because DNAT does not modify the source address. This is a standard port forwarding scenario.
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 →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are a network administrator for a medium-sized company. The company has a Linux server acting as a router/firewall with three network interfaces: eth0 (public, 203.0.113.2/24, gateway 203.0.113.1), eth1 (DMZ, 10.0.1.1/24), and eth2 (internal, 192.168.1.1/24). The DMZ hosts a web server with IP 10.0.1.100, and the internal network has client machines. The firewall rules are currently set to default DROP on INPUT and FORWARD, ACCEPT on OUTPUT. The administrator wants to allow internal clients (192.168.1.0/24) to access the web server (10.0.1.100) on port 80. Additionally, the administrator wants to allow external users (from the internet) to access the web server's public IP (203.0.113.2) on port 80, which should be DNATed to 10.0.1.100. The administrator has enabled IP forwarding and added the following rules:
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to-destination 10.0.1.100:80
iptables -A FORWARD -i eth0 -o eth1 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -p tcp --sport 80 -j ACCEPT
Internal clients cannot access the web server. External users are able to access the web server successfully. What is the most likely reason internal clients cannot access the web server?
hard
✓ A.The DNAT rule does not apply to traffic coming from the internal network because it is not received on eth0.
B.The web server cannot route back to the internal clients because it is in the DMZ.
C.The FORWARD rule for return traffic does not match because the destination is the client.
D.IP forwarding is not enabled for the internal interface.
Why A: The DNAT rule is placed in the PREROUTING chain of the nat table, which only processes packets arriving on the specified interface (eth0). Internal clients (192.168.1.0/24) sending traffic to the web server (10.0.1.100) do not enter via eth0; they are routed through eth2. Therefore, the DNAT rule never matches their packets, and the destination remains 10.0.1.100, which is directly reachable without NAT. However, the FORWARD rules only allow traffic from eth0 to eth1 and back, so internal client traffic from eth2 to eth1 is implicitly dropped by the default FORWARD policy, causing the failure.
Last reviewed: Jun 11, 2026
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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.
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