LPIC-2 Advanced Networking Configuration Practice Question
This LPIC-2 practice question tests your understanding of advanced networking configuration. 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.
Exhibit
Refer to the exhibit.
# ip rule show
0: from all lookup local
32766: from all lookup main
32767: from all lookup default
# ip route show table 100
default via 10.0.0.1 dev eth0
# ip route show table 200
default via 172.16.0.1 dev eth1
# ip rule add from 10.1.1.0/24 lookup 200
# ip rule add from 10.2.2.0/24 lookup 100
Traffic from the 10.1.1.0/24 subnet is seen leaving through eth1 as intended, but reply traffic from the internet never comes back. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Clue: "never"
Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
Refer to the exhibit.
# ip rule show
0: from all lookup local
32766: from all lookup main
32767: from all lookup default
# ip route show table 100
default via 10.0.0.1 dev eth0
# ip route show table 200
default via 172.16.0.1 dev eth1
# ip rule add from 10.1.1.0/24 lookup 200
# ip rule add from 10.2.2.0/24 lookup 100
A
The kernel parameter net.ipv4.conf.all.rp_filter is set to 1.
Strict reverse path filtering drops packets arriving on an interface that would not be used to reach the source, which commonly happens in asymmetric routing scenarios.
B
The ip rule priority is not set, causing it to be overridden.
Why wrong: Rules without explicit priority are assigned automatically and still apply.
C
The default route in table 200 points to 172.16.0.1 which does not have a route back to 10.1.1.0/24.
Why wrong: The remote gateway may have routes; but the typical issue with policy routing is reverse path filtering.
D
The router does not have a route back to 10.1.1.0/24 via eth0.
Why wrong: The router likely has a route; the issue is not lack of route but the reverse path check.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The kernel parameter net.ipv4.conf.all.rp_filter is set to 1.
When `net.ipv4.conf.all.rp_filter` is set to 1, the kernel performs strict reverse path filtering. This means the kernel checks whether the source address of incoming packets can be reached via the interface they arrived on. If reply traffic from the internet arrives on an interface (e.g., eth0) that does not have a route back to the original source subnet (10.1.1.0/24) through that same interface, the kernel drops the packet. This is the most likely cause because the outbound traffic leaves via eth1, but the reply comes back on a different interface, triggering the rp_filter check and causing the reply to be silently discarded.
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 kernel parameter net.ipv4.conf.all.rp_filter is set to 1.
Why this is correct
Strict reverse path filtering drops packets arriving on an interface that would not be used to reach the source, which commonly happens in asymmetric routing scenarios.
Clue confirmation
The clue words "most likely", "never" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The ip rule priority is not set, causing it to be overridden.
Why it's wrong here
Rules without explicit priority are assigned automatically and still apply.
✗
The default route in table 200 points to 172.16.0.1 which does not have a route back to 10.1.1.0/24.
Why it's wrong here
The remote gateway may have routes; but the typical issue with policy routing is reverse path filtering.
✗
The router does not have a route back to 10.1.1.0/24 via eth0.
Why it's wrong here
The router likely has a route; the issue is not lack of route but the reverse path check.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the issue is a missing return route or a routing table misconfiguration, but the real culprit is the kernel's reverse path filtering, which silently drops packets that arrive on an interface that is not the best path back to the source.
Detailed technical explanation
How to think about this question
Reverse path filtering is implemented in the Linux kernel's `fib_validate_source()` function, which performs a route lookup for the source IP of the incoming packet. If the best route for that source IP does not point back to the interface the packet arrived on, the packet is dropped. This is a common security measure against IP spoofing, but it can break asymmetric routing scenarios where traffic leaves via one interface and returns via another. The sysctl parameter `net.ipv4.conf.all.rp_filter` applies to all interfaces, while per-interface settings like `net.ipv4.conf.eth0.rp_filter` can override it.
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 kernel parameter net.ipv4.conf.all.rp_filter is set to 1. — When `net.ipv4.conf.all.rp_filter` is set to 1, the kernel performs strict reverse path filtering. This means the kernel checks whether the source address of incoming packets can be reached via the interface they arrived on. If reply traffic from the internet arrives on an interface (e.g., eth0) that does not have a route back to the original source subnet (10.1.1.0/24) through that same interface, the kernel drops the packet. This is the most likely cause because the outbound traffic leaves via eth1, but the reply comes back on a different interface, triggering the rp_filter check and causing the reply to be silently discarded.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "never". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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.