CCNA Network Infrastructure and Connectivity Practice Question
Which TWO statements about fiber optic cables and SFP/SFP+ transceivers are correct?
⚠ Common exam trap
Cisco often tests the misconception that 'multimode' implies longer reach due to its name, but the opposite is true because of modal dispersion limits.
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
✓
Single-mode fiber (SMF) uses a smaller core diameter than multimode fiber (MMF).
Single-mode fiber (SMF) has a core diameter of about 9 microns, which is smaller than multimode fiber (MMF) cores of 50 or 62.5 microns. Option C is correct because SFP+ transceivers are indeed designed for 10 Gigabit Ethernet, supporting data rates up to 10 Gbps. Option B is wrong because multimode fiber is used for shorter distances (up to a few hundred meters) due to higher modal dispersion, while single-mode fiber supports longer distances (tens of kilometers). Option D is wrong because standard SFP modules support up to 1 Gbps, not 10 Gbps; SFP+ modules handle 10 Gbps. Option E is wrong because a 9-micron core is characteristic of single-mode fiber, not multimode fiber.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Single-mode fiber (SMF) uses a smaller core diameter than multimode fiber (MMF).
Why this is correct
Single-mode fiber is engineered with a much smaller core—typically 9 microns—compared to multimode fiber's 50- or 62.5-micron core. This narrow core forces light to travel in a single straight path, virtually eliminating modal dispersion. As a result, SMF supports longer transmission distances and higher bandwidth than MMF, which is why it is used for long-haul and carrier-grade links.
- ✗
Multimode fiber supports longer distances than single-mode fiber.
Why it's wrong here
This statement is incorrect because multimode fiber suffers from higher modal dispersion due to its larger core, which allows multiple light paths (modes) to travel at different speeds. These modes arrive at the receiver at different times, causing pulse spreading and limiting the practical distance to a few hundred meters. Single-mode fiber, by contrast, supports distances of many kilometers because its small core permits only one mode, so dispersion is far lower.
- ✓
SFP+ transceivers are commonly used for 10 Gigabit Ethernet connections.
Why this is correct
SFP+ (Enhanced Small Form-Factor Pluggable) transceivers are specifically designed to support data rates up to 10 Gbps, making them a standard choice for 10 Gigabit Ethernet connections. They use the same mechanical form factor as standard SFP modules but are engineered for higher-speed signaling, often with higher-grade optics and improved heat dissipation. SFP+ is widely deployed in data centers, enterprise switches, and storage networks for 10GbE uplinks.
- ✗
SFP modules support data rates up to 10 Gbps.
Why it's wrong here
Standard SFP modules are rated for data rates up to 1 Gbps, commonly used for 100BASE-TX and 1000BASE-X (Gigabit Ethernet) connections. They are not designed to handle 10 Gbps signaling; that capability belongs to SFP+ modules, which have tighter electrical and optical specifications. Confusing SFP with SFP+ is a common mistake because of their identical physical size, but their performance limits are distinctly different.
- ✗
Multimode fiber typically has a core diameter of 9 microns.
Why it's wrong here
This statement is factually incorrect because multimode fiber uses a larger core diameter, typically 50 microns (OM2-OM5) or 62.5 microns (OM1). The 9-micron core is a characteristic of single-mode fiber, which is designed to support a single propagation mode. Assigning the 9-micron diameter to MMF reveals a misunderstanding of the fundamental structural difference between the two fiber types.
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.
✓Single-mode fiber (SMF) uses a smaller core diameter than multimode fiber (MMF).Correct answer▾
Why this is correct
Single-mode fiber is engineered with a much smaller core—typically 9 microns—compared to multimode fiber's 50- or 62.5-micron core. This narrow core forces light to travel in a single straight path, virtually eliminating modal dispersion. As a result, SMF supports longer transmission distances and higher bandwidth than MMF, which is why it is used for long-haul and carrier-grade links.
✗Multimode fiber supports longer distances than single-mode fiber.Wrong answer — click to see why▾
Why this is wrong here
Single-mode fiber supports much longer distances (up to 10 km or more) than multimode fiber (typically up to 550 m for 10 Gbps).
✗SFP modules support data rates up to 10 Gbps.Wrong answer — click to see why▾
Why this is wrong here
SFP is limited to 1 Gbps; for 10 Gbps, SFP+ is required.
✗Multimode fiber typically has a core diameter of 9 microns.Wrong answer — click to see why▾
Why this is wrong here
This describes single-mode fiber, not multimode.
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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