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.
Exhibit
Refer to the exhibit.
# brctl show
bridge name bridge id STP enabled interfaces
br0 8000.001122334455 yes eth0
eth1
# brctl showstp br0
br0
bridge id 8000.001122334455
designated root 8000.001122334455
root port 0 path cost 0
max age 20.00
hello time 2.00
forward delay 15.00
bridge hello time 2.00
bridge max age 20.00
bridge forward delay 15.00
ageing time 300.00
hello timer 0.00
tcn timer 0.00
topology change timer 0.00
gc timer 0.00
eth0 (1)
port id 8001 state forwarding
designated root 8000.001122334455 path cost 4
designated bridge 8000.001122334455 message age timer 0.00
designated port 8001 forward delay timer 0.00
designated cost 0 hold timer 0.00
eth1 (2)
port id 8002 state blocking
designated root 8000.001122334455 path cost 4
designated bridge 8000.001122334455 message age timer 0.00
designated port 8002 forward delay timer 0.00
designated cost 0 hold timer 0.00
Hosts connected to eth1 cannot communicate with hosts on eth0. Based on the exhibit, what is the most likely reason?
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
✓
Spanning Tree Protocol has placed eth1 in blocking state.
The exhibit shows a Linux bridge (br0) with eth0 and eth1 as bridge ports. If hosts on eth1 cannot communicate with hosts on eth0, the most likely cause is that Spanning Tree Protocol (STP) has placed eth1 in a blocking state to prevent a Layer 2 loop. STP blocks redundant paths by transitioning ports through listening, learning, and blocking states, and a blocked port does not forward traffic until the topology converges.
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.
✗
Physical layer issues on eth1.
Why it's wrong here
No indicator of physical issues; the link is up (state is blocking, not down).
✗
Eth1 is not connected to the bridge.
Why it's wrong here
Eth1 is listed as an interface of br0.
✓
Spanning Tree Protocol has placed eth1 in blocking state.
Why this is correct
The state 'blocking' for eth1 means STP is preventing forwarding to avoid loops.
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 bridge interface has no IP address.
Why it's wrong here
Bridges operate at L2 and do not require an IP for forwarding.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a missing IP address on the bridge interface prevents inter-VLAN or inter-host communication, but STP blocking is the actual Layer 2 issue that stops traffic between bridge ports.
Detailed technical explanation
How to think about this question
STP (IEEE 802.1D) elects a root bridge and calculates the shortest path to it, placing redundant ports in a blocking state to prevent broadcast storms and MAC address table instability. In Linux, STP can be enabled on a bridge via 'brctl stp <bridge> on' or 'ip link set <bridge> type bridge stp_state 1'; a blocked port will show 'state blocking' in 'bridge link show' output. A real-world scenario is when a network administrator adds a second uplink to a bridge without disabling STP, causing one port to block until the topology recalculates, which can take 30-50 seconds.
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: Spanning Tree Protocol has placed eth1 in blocking state. — The exhibit shows a Linux bridge (br0) with eth0 and eth1 as bridge ports. If hosts on eth1 cannot communicate with hosts on eth0, the most likely cause is that Spanning Tree Protocol (STP) has placed eth1 in a blocking state to prevent a Layer 2 loop. STP blocks redundant paths by transitioning ports through listening, learning, and blocking states, and a blocked port does not forward traffic until the topology converges.
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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