Cisco CCNA Physical Interfaces, Cabling, and Interface Errors

Question 1

What is the maximum supported segment length for 1000BASE-T over Cat5e/Cat6 UTP copper?

Accepted Answer

100 meters

Answer

1000BASE-T, like 10BASE-T and 100BASE-TX, supports runs of up to 100 meters on twisted-pair copper. Longer distances need fiber.

Question 2

Which statement correctly compares single-mode fiber with multimode fiber?

Accepted Answer

Single-mode has a smaller core, usually uses lasers, and supports much longer distances

Answer

Single-mode fiber has a narrow core of about 9 µm and usually uses a laser light source. This reduces modal dispersion and allows runs of many kilometers. Multimode has a wider core (50/62.5 µm), uses cheaper LEDs or VCSELs, and is limited to shorter distances.

Question 3

'show interfaces' on a switch port shows a growing count of late collisions. What is the most likely cause?

Accepted Answer

A duplex mismatch

Answer

Late collisions are the classic sign of a duplex mismatch. The half-duplex side detects collisions after the first 64 bytes because the full-duplex side transmits whenever it wants. Cables longer than spec can also cause them, but duplex mismatch is the usual answer.

Question 4

An interface shows a steadily rising number of CRC errors but no collisions, and both ends are set to full duplex. What is the most likely cause?

Accepted Answer

A bad cable, a bad connector, or electromagnetic interference

Answer

CRC errors mean the frames arrived corrupted. With duplex set correctly on both ends, the likely cause is the physical layer: a damaged cable or connector, EMI, or a cable longer than spec.

Question 5

What does Auto-MDIX do on a switch port?

Accepted Answer

It detects the cable type and adjusts transmit/receive pairs, so either straight-through or crossover cable works

Answer

Auto-MDIX automatically swaps the transmit and receive pairs as needed. This removes the need to choose between straight-through and crossover cables when connecting similar or different devices.

Cisco CCNA Practice Test

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Cisco CCNA Physical Interfaces, Cabling, and Interface Errors