Quick Answer
The answer is 1000BASE-LX, the correct transceiver for a 2 km single-mode fiber link. This standard uses long wavelength laser light at 1310 nm, which travels efficiently through single-mode fiber’s narrow core, supporting distances up to 5 km and often 10 km with proper link budgets—well beyond the 550 m limit of multimode fiber. On the CompTIA Network+ N10-009 exam, this question tests your ability to match transceiver types to distance and fiber specifications, often appearing in scenario-based questions about campus or building-to-building connections. A common trap is confusing 1000BASE-SX (which only works up to 550 m over multimode) with LX, or assuming LX requires multimode fiber. Remember the memory tip: “LX for Long haul, SX for Short”—LX uses single-mode for extended runs, while SX is limited to short multimode links.
This N10-009 practice question tests your understanding of network implementation. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 network administrator needs to connect two buildings 2 km apart using single-mode fiber. Which transceiver type should be used?
1000BASE-T
Why wrong: 1000BASE-T uses twisted-pair copper and is limited to 100 meters.
1000BASE-SX
Why wrong: 1000BASE-SX uses multimode fiber and supports distances up to 550 meters, insufficient for 2 km.
1000BASE-LX
1000BASE-LX operates over single-mode fiber and can reach distances of 5 km or more.
10GBASE-SR
Why wrong: 10GBASE-SR is a 10 Gbps standard for multimode fiber, typically limited to 400 meters.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
1000BASE-LX
1000BASE-LX (Long Wavelength) operates at 1310 nm over single-mode fiber and supports distances up to 5 km (and often up to 10 km with proper link budgets), making it the correct choice for a 2 km link. Single-mode fiber is required for distances beyond 550 m, and 1000BASE-LX is the Gigabit Ethernet standard designed for such single-mode runs.
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.
1000BASE-T
Why it's wrong here
1000BASE-T uses twisted-pair copper and is limited to 100 meters.
1000BASE-SX
Why it's wrong here
1000BASE-SX uses multimode fiber and supports distances up to 550 meters, insufficient for 2 km.
1000BASE-LX
Why this is correct
1000BASE-LX operates over single-mode fiber and can reach distances of 5 km or more.
Related concept
Read the scenario before looking for a memorised answer.
10GBASE-SR
Why it's wrong here
10GBASE-SR is a 10 Gbps standard for multimode fiber, typically limited to 400 meters.
Common exam traps
Cisco often tests the misconception that 1000BASE-SX can be used for long distances because it is a common Gigabit Ethernet standard, but the trap is that SX is strictly for multimode fiber and limited to 550 m, while LX is the correct choice for single-mode runs beyond that distance.
Detailed technical explanation
1000BASE-LX uses a 1310 nm laser and can run over both single-mode and multimode fiber, but when used with multimode fiber, a mode-conditioning patch cord is required to prevent differential mode delay. The actual reach on single-mode fiber is often limited by the optical power budget and receiver sensitivity; typical 1000BASE-LX optics can achieve up to 10 km, and some extended-reach variants (1000BASE-EX) can go up to 40 km. In a real-world campus deployment, the administrator must also verify the fiber type (OS1/OS2) and ensure the transceiver's optical output power and receive sensitivity match the link loss budget.
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 N10-009 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
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
The correct answer is: 1000BASE-LX — 1000BASE-LX (Long Wavelength) operates at 1310 nm over single-mode fiber and supports distances up to 5 km (and often up to 10 km with proper link budgets), making it the correct choice for a 2 km link. Single-mode fiber is required for distances beyond 550 m, and 1000BASE-LX is the Gigabit Ethernet standard designed for such single-mode runs.
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 11, 2026
This N10-009 practice question is part of Courseiva's free CompTIA 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 N10-009 exam.
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