CCNA Network Infrastructure and Connectivity Practice Question

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) typically uses a larger core diameter than multimode fiber (MMF).

  Why it's wrong here

  Single-mode fiber (SMF) has a much smaller core diameter than multimode fiber (MMF). SMF typically uses a 9-micron core with a 125-micron cladding (9/125 µm), while MMF cores are either 50 or 62.5 microns (50/125 µm or 62.5/125 µm). Because the core is so narrow, SMF permits only a single propagation path (mode) for light, which is the opposite of the claim in the statement.

• ✗

  Multimode fiber (MMF) is generally preferred for longer-distance links, such as between buildings on a campus network.

  Why it's wrong here

  Multimode fiber is not preferred for longer-distance campus links because its larger core allows multiple light paths, causing modal dispersion that broadens pulses and limits the usable distance. Single-mode fiber, with lower attenuation and essentially no modal dispersion, is the standard choice for building-to-building or WAN distances, often reaching 10 km or more with appropriate optics. MMF is instead used for shorter reaches such as within a data center or access-floor cabling.

• ✗

  A 1000BASE-LX SFP transceiver operating over single-mode fiber can support distances up to 10 km.

  Why it's wrong here

  The 1000BASE-LX standard over single-mode fiber supports distances up to 5 km, not 10 km. Some transceivers may support longer distances with additional optics, but the standard specification is 5 km, making this statement inaccurate.

  When this WOULD be correct

  In enterprise networks, 1000BASE-LX SFP transceivers are commonly used for long-haul links over single-mode fiber, supporting distances up to 10 km. This makes them ideal for connecting geographically separated buildings or campus backbones where cost-effective gigabit connectivity over several kilometers is required.

• ✓

  When using a 10GBASE-SR SFP+ transceiver over OM3 multimode fiber, the maximum supported distance is 300 meters.

  Why this is correct

  Under IEEE 802.3ae, a 10GBASE-SR SFP+ transceiver operating over OM3 multimode fiber supports a maximum link length of 300 meters. OM3 is a laser-optimized 50/125 µm fiber with an effective modal bandwidth of 2000 MHz·km at 850 nm, which is the wavelength used by the short-range VCSEL optic in 10GBASE-SR. This 300-meter limit specifically applies to OM3; OM4 raises the distance to 400 meters, while OM2 supports only about 82 meters at 10 Gbps.

• ✓

  Fiber optic cabling is immune to electromagnetic interference (EMI), making it ideal for environments with high electrical noise.

  Why this is correct

  Fiber optic cabling transmits data as pulses of light through glass or plastic strands rather than as electrical signals on copper conductors, so it cannot conduct current and is inherently immune to electromagnetic interference (EMI). This makes fiber ideal for installations near motors, generators, heavy machinery, or power cables where copper would suffer from noise-induced errors. The absence of metallic conductors also prevents ground loops and reduces the risk of lightning surge damage.

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.

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?”