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 wants to set up a Linux bridge to connect a wireless interface (wlan0) to a wired interface (eth0) to allow devices on the wired network to access the internet through the wireless uplink. The Linux server runs Debian with hostapd to create an access point on wlan0. The administrator creates a bridge br0 using brctl and adds eth0 and wlan0 as ports. They assign IP 192.168.10.1/24 to br0 and start hostapd. Clients on the wired network can access the internet, but cannot ping clients on the wireless network, and vice versa. The administrator verifies that both interfaces are enslaved to br0 (brctl show shows both). They also confirm that IP forwarding is enabled and there are no iptables rules blocking anything. Which of the following 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The wireless interface wlan0 is not set to 4-address mode (WDS) to allow bridging.
A is correct because a standard wireless interface (station mode) uses 3-address frames (source, destination, BSSID) and drops frames with a fourth address, which is required for bridging. When a bridge forwards a frame from the wired side to the wireless side, it uses the MAC addresses of the original source and destination, but the wireless medium requires the fourth address (the transmitter address) to identify the bridge itself. Without enabling 4-address mode (WDS) on wlan0, the wireless driver will reject these bridged frames, preventing communication between wired and wireless clients.
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 wireless interface wlan0 is not set to 4-address mode (WDS) to allow bridging.
Why this is correct
Bridging requires 4-address frames on wireless interfaces.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The DHCP server is only listening on the bridge interface, not on the individual interfaces.
Why it's wrong here
DHCP server listening on br0 is sufficient since both networks are bridged.
✗
The hostapd configuration is missing the 'bridge' parameter to bind to the bridge.
Why it's wrong here
hostapd's bridge parameter is for adding the AP interface, but wlan0 is already in bridge.
✗
The iptables firewall is blocking broadcast traffic between bridge ports.
Why it's wrong here
No iptables rules are present.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume bridging works identically on wireless and wired interfaces, overlooking the 802.11 frame format limitation that requires 4-address mode for transparent bridging.
Detailed technical explanation
How to think about this question
In IEEE 802.11, standard station mode uses 3-address frames (DA, SA, BSSID) for data frames; bridging requires 4-address frames (adding the transmitter address) to allow the access point to forward frames from the wired network to wireless clients without modifying the source MAC. Enabling 4-address mode (often called WDS or 'bridge mode') on the wireless interface tells the driver to accept and transmit these extended frames. In practice, many wireless drivers require setting the interface to 'ap' mode with 'wds' flag or using 'iw dev wlan0 set 4addr on' before adding it to the bridge.
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 wireless interface wlan0 is not set to 4-address mode (WDS) to allow bridging. — A is correct because a standard wireless interface (station mode) uses 3-address frames (source, destination, BSSID) and drops frames with a fourth address, which is required for bridging. When a bridge forwards a frame from the wired side to the wireless side, it uses the MAC addresses of the original source and destination, but the wireless medium requires the fourth address (the transmitter address) to identify the bridge itself. Without enabling 4-address mode (WDS) on wlan0, the wireless driver will reject these bridged frames, preventing communication between wired and wireless clients.
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". 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.
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Question Discussion
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