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.
A Linux administrator is setting up an IPsec VPN between two sites using strongSwan. The VPN established successfully, but traffic between the sites is not being encrypted. What is the most probable cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The IPsec policies are not configured to match the traffic.
Option A is correct because the most probable cause for traffic not being encrypted after a successful IPsec tunnel establishment is that the IPsec policies (e.g., strongSwan's `ipsec.conf` `conn` section with `leftsubnet`/`rightsubnet`) do not match the actual traffic flows. Even if the IKE/SA is up, strongSwan only applies encryption to packets that match the configured selectors; mismatched subnets or protocols result in cleartext traffic bypassing the tunnel.
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 IPsec policies are not configured to match the traffic.
Why this is correct
The SPD defines which traffic should be encrypted; without matching policies, traffic flows in plain text.
Related concept
Read the scenario before looking for a memorised answer.
✗
The firewall is blocking UDP port 500.
Why it's wrong here
UDP 500 is needed for IKE; if it were blocked, the VPN would not establish.
✗
The kernel does not support IPsec (net.ipv4.ip_forward=0).
Why it's wrong here
ip_forward is not related to IPsec; it controls routing, not encryption.
✗
The IPsec daemon is not started.
Why it's wrong here
If the daemon were not started, the VPN would not establish at all.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a successful IKE/SA establishment guarantees encryption for all traffic, but LPIC-2 tests the understanding that IPsec policies (SPD selectors) independently control which packets are encrypted, and a mismatch leaves traffic unencrypted.
Detailed technical explanation
How to think about this question
In strongSwan, IPsec policies are defined by Security Policy Database (SPD) entries derived from `leftsubnet`/`rightsubnet` in `ipsec.conf`. The kernel's XFRM framework uses these SPD selectors (source/destination IP, protocol, ports) to decide whether to apply encryption (via SA lookup) or bypass. A common real-world mistake is using `0.0.0.0/0` as a subnet, which may match all traffic but can conflict with other routes; alternatively, forgetting to include specific subnets causes traffic to fall through to the default `bypass` policy.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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 IPsec policies are not configured to match the traffic. — Option A is correct because the most probable cause for traffic not being encrypted after a successful IPsec tunnel establishment is that the IPsec policies (e.g., strongSwan's `ipsec.conf` `conn` section with `leftsubnet`/`rightsubnet`) do not match the actual traffic flows. Even if the IKE/SA is up, strongSwan only applies encryption to packets that match the configured selectors; mismatched subnets or protocols result in cleartext traffic bypassing the tunnel.
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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