CCNA Network Infrastructure and Connectivity Practice Question
Which TWO statements about fiber optic cable types and SFP transceivers are correct?
⚠ Common exam trap
Cisco often tests the misconception that SFP+ is backward compatible with SFP at the same speed, when in fact SFP+ is a 10 Gbps standard and requires specific port support or auto-negotiation to operate with 1 Gbps SFP modules.
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
✓
Multimode fiber is commonly used in campus and data center environments for distances up to several hundred meters.
Multimode fiber (MMF) has a larger core (typically 50/125 µm or 62.5/125 µm) and is used for short-reach, cost-effective connections up to a few hundred meters, making option B correct. Single-mode fiber (SMF) uses a much smaller core (~9 µm) and laser-based optics to achieve distances of 10 km or more, so option D is correct. Option A is wrong because it reverses the core size characteristic: SMF has a smaller core, and the given dimensions (62.5/125 µm) refer to multimode. Option C is wrong because SFP+ is a 10 Gbps form factor and is not inherently backward compatible with 1 Gbps SFP modules unless the switch port explicitly supports dual-rate operation. Option E is incorrect because fiber optic cables are inherently immune to electromagnetic interference (EMI) and therefore never require EMI shielding in any environment; the false statement claims they need shielding.
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 uses a larger core (typically 62.5/125 µm) and supports longer distances than multimode fiber.
Why it's wrong here
Single-mode fiber's core is not larger; it is typically 9/125 µm, while multimode fiber uses 50/125 µm or 62.5/125 µm cores. The smaller core constrains light to a single mode, eliminating modal dispersion and enabling longer transmission distances. Thus, mixing up the core diameters reverses the fundamental design difference that makes single-mode the long-haul choice.
- ✓
Multimode fiber is commonly used in campus and data center environments for distances up to several hundred meters.
Why this is correct
Multimode fiber is indeed the predominant medium for campus and data center links because its larger core and high numerical aperture permit the use of low-cost VCSELs or LEDs, and it provides sufficient bandwidth for reaches of 300–550 m at 10 Gbps using OM3/OM4 grades. Beyond these distances, modal dispersion becomes the limiting factor, making single-mode fiber more appropriate for longer backbone or WAN links.
- ✗
SFP+ transceivers support data rates up to 1 Gbps and are backward compatible with standard SFP modules.
Why it's wrong here
SFP+ transceivers operate at 10 Gbps, not 1 Gbps; SFP modules are the 1 Gbps version. Although many SFP+ ports are physically compatible with SFP modules and will auto-negotiate down to 1 Gbps, the reverse is not true: an SFP+ module cannot be inserted into a standard SFP port designed only for 1 Gbps, so the claimed backward compatibility is one-way and only in the port, not in the module.
- ✓
Single-mode fiber typically uses laser-based transceivers and can support distances exceeding 10 km.
Why this is correct
Single-mode fiber relies on narrow-core (9/125 µm) construction and laser-based optical sources, usually at 1310 nm or 1550 nm, where attenuation and dispersion are minimized. These characteristics allow transmission distances beyond 10 km, with common transceivers reaching 40 km or even 80 km in dense WDM systems. The laser's coherent, low-divergence beam couples efficiently into the small core, preserving signal integrity over long spans.
- ✗
Fiber optic cables must be run with EMI shielding when deployed in environments with high electromagnetic interference.
Why it's wrong here
Fiber optic cables carry light pulses in glass or plastic cores and are therefore completely immune to electromagnetic interference, so EMI shielding is never required for the transmission medium itself. The common phrase about 'shielding' actually refers to copper cabling, where metallic braid or foil prevents external noise from corrupting data. While fiber may need armored jackets for mechanical protection in harsh environments, that is a physical durability requirement, not an electromagnetic one.
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.
✓Multimode fiber is commonly used in campus and data center environments for distances up to several hundred meters.Correct answer▾
Why this is correct
Multimode fiber is indeed the predominant medium for campus and data center links because its larger core and high numerical aperture permit the use of low-cost VCSELs or LEDs, and it provides sufficient bandwidth for reaches of 300–550 m at 10 Gbps using OM3/OM4 grades. Beyond these distances, modal dispersion becomes the limiting factor, making single-mode fiber more appropriate for longer backbone or WAN links.
✗Single-mode fiber uses a larger core (typically 62.5/125 µm) and supports longer distances than multimode fiber.Wrong answer — click to see why▾
Why this is wrong here
This statement incorrectly describes the core size of single-mode fiber.
✗SFP+ transceivers support data rates up to 1 Gbps and are backward compatible with standard SFP modules.Wrong answer — click to see why▾
Why this is wrong here
The data rate is incorrectly stated as 1 Gbps instead of 10 Gbps.
✗Fiber optic cables must be run with EMI shielding when deployed in environments with high electromagnetic interference.Wrong answer — click to see why▾
Why this is wrong here
Fiber is immune to electromagnetic interference and never requires EMI shielding.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco 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 200-301 exam.