CCNA Network Infrastructure and Connectivity Practice Question
Which TWO statements about SFP transceivers and fiber optic cabling are correct?
⚠ Common exam trap
Cisco often tests the misconception that multimode fiber always uses lasers for long distances, when in fact multimode fiber is optimized for shorter runs with LED or VCSEL sources, while single-mode fiber uses lasers for extended reach.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
1000BASE-SX SFP transceivers are designed for multimode fiber and typically support distances up to 550 meters.
1000BASE-SX SFP transceivers are designed for multimode fiber (MMF) and use short-wavelength lasers (850 nm). Over 50/125 µm MMF, they support up to 550 meters. Option D is correct because 1000BASE-LX SFP transceivers are designed for single-mode fiber (SMF) and support distances up to 5 km according to the IEEE 802.3 standard (not 10 km, which is typically a vendor-specific LH extension). Option A is false because SFPs are hot-swappable pluggable modules, not permanently installed. Option C is false because multimode fiber typically uses LED or VCSEL transmitters for short distances, not lasers for long-haul. Option E is false because single-mode fiber has a smaller core diameter (8-10 µm) than multimode fiber (50-62.5 µm), which reduces modal dispersion and allows longer distances.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
SFP transceivers are permanently installed on the switch motherboard and cannot be replaced.
Why it's wrong here
SFP transceivers are hot-swappable and can be inserted or removed without powering down the switch, allowing easy media changes.
- ✓
1000BASE-SX SFP transceivers are designed for multimode fiber and typically support distances up to 550 meters.
Why this is correct
1000BASE-SX uses multimode fiber with a 850 nm wavelength and supports distances up to 550 m (depending on fiber grade).
- ✗
Multimode fiber typically uses laser-based transmitters for long-distance transmission.
Why it's wrong here
Multimode fiber uses LED or VCSEL (Vertical-Cavity Surface-Emitting Laser) sources that are less expensive but limited to shorter distances.
- ✓
Single-mode fiber (SMF) with 1000BASE-LX SFP transceivers can support distances up to 5 km.
Why this is correct
1000BASE-LX SFP transceivers are designed for single-mode fiber and support a maximum distance of 5 km according to IEEE 802.3z. Vendor-specific 'LX/LH' transceivers may extend this to 10 km, but the CCNA exam focuses on standard specifications.
- ✗
Single-mode fiber has a larger core diameter than multimode fiber, allowing longer distances.
Why it's wrong here
Single-mode fiber has a much smaller core (about 9 microns) compared to multimode (50 or 62.5 microns). The smaller core reduces modal dispersion, enabling longer distances.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓1000BASE-SX SFP transceivers are designed for multimode fiber and typically support distances up to 550 meters.Correct answer▾
Why this is correct
1000BASE-SX uses multimode fiber with a 850 nm wavelength and supports distances up to 550 m (depending on fiber grade).
✗SFP transceivers are permanently installed on the switch motherboard and cannot be replaced.Wrong answer — click to see why▾
Why this is wrong here
This statement is false because SFP slots are designed for modular, replaceable transceivers.
✗Multimode fiber typically uses laser-based transmitters for long-distance transmission.Wrong answer — click to see why▾
Why this is wrong here
Laser transmitters are used in single-mode fiber for longer distances; multimode uses LED/VCSEL.
✗Single-mode fiber has a larger core diameter than multimode fiber, allowing longer distances.Wrong answer — click to see why▾
Why this is wrong here
Single-mode fiber has a smaller core, not larger. The smaller core reduces dispersion and allows longer reach.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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