This LFCS practice question tests your understanding of networking. 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 system administrator wants to combine two network interfaces for increased throughput and fault tolerance. The requirement is that both links are active simultaneously and the system can tolerate a failure of one link without interruption. Which bonding mode should be used?
Mode 4 (802.3ad)
Combines links for throughput and fails over if a link goes down.
Mode 2 (balance-xor)
Why wrong: Requires switch configuration and does not inherently handle failover.
Mode 1 (active-backup)
Why wrong: Only one link is active at a time.
Mode 0 (balance-rr)
Why wrong: Provides load balancing but not fault tolerance without additional configuration.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Mode 4 (802.3ad)
Mode 4 (802.3ad) is correct because it implements IEEE 802.3ad Link Aggregation Control Protocol (LACP), which allows both links to be active simultaneously for increased throughput while providing fault tolerance. If one link fails, traffic is automatically redistributed across the remaining active links without interruption, meeting the requirement for both active links and failure tolerance.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Mode 4 (802.3ad)
Why this is correct
Combines links for throughput and fails over if a link goes down.
Related concept
Read the scenario before looking for a memorised answer.
Mode 2 (balance-xor)
Why it's wrong here
Requires switch configuration and does not inherently handle failover.
Mode 1 (active-backup)
Why it's wrong here
Only one link is active at a time.
Mode 0 (balance-rr)
Why it's wrong here
Provides load balancing but not fault tolerance without additional configuration.
Common exam traps
The trap here is that candidates often confuse Mode 4 (802.3ad) with Mode 0 (balance-rr) because both allow active links, but Mode 0 lacks the standardized LACP negotiation and seamless failover that Mode 4 provides, leading to incorrect selection when fault tolerance is explicitly required.
Detailed technical explanation
Under the hood, Mode 4 uses LACP to negotiate aggregation with the switch, requiring both the server and switch to support and be configured for 802.3ad. The bonding driver uses a hash policy (e.g., based on MAC addresses or IPs) to distribute traffic across links, and LACP monitors link health via periodic LACPDUs, ensuring rapid failover (typically within seconds) without manual intervention. In real-world scenarios, this mode is essential for high-availability storage or web servers where both throughput and uptime are critical.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the LFCS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
The correct answer is: Mode 4 (802.3ad) — Mode 4 (802.3ad) is correct because it implements IEEE 802.3ad Link Aggregation Control Protocol (LACP), which allows both links to be active simultaneously for increased throughput while providing fault tolerance. If one link fails, traffic is automatically redistributed across the remaining active links without interruption, meeting the requirement for both active links and failure tolerance.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.
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