Question 72 of 1,020

Cabling →easyMultiple ChoiceObjective-mapped

Why Gigabit Ethernet Drops to 100 Mbps: Cat5 Cable

This 220-1201 practice question tests your understanding of cabling. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A customer reports that their new Gigabit Ethernet connection is only achieving 100 Mbps speeds. The cable run is about 75 meters through a drop ceiling. You verify the switch and NIC are both Gigabit-capable. Which cable issue is most likely causing the speed limitation?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The cable is a Cat5e patch cable.
Why wrong: Cat5e supports Gigabit Ethernet up to 100 meters, so this would not cause a 100 Mbps limit.
B
The cable is a Cat6a cable.
Why wrong: Cat6a exceeds Gigabit requirements, so it would not cause a speed drop to 100 Mbps.
C
The cable is a Cat5 cable.
Cat5 cable is only rated for 100 Mbps, so using it for a Gigabit connection would limit speed to 100 Mbps.
D
The cable is a Cat6 cable.
Why wrong: Cat6 supports Gigabit Ethernet, so it would not cause a speed limitation.

Full breakdown with real-world context →

Quick Answer

The answer is that the cable is a Cat5 cable, which is the most likely cause of the speed limitation. While Cat5e and Cat6 cables support Gigabit Ethernet up to the full 100-meter distance, the older Cat5 standard was only certified for 100 Mbps, so using it will cap your connection regardless of the switch or NIC capabilities. On the CompTIA A+ Core 1 220-1201 exam, this tests your understanding of Ethernet cabling standards and their speed limitations, often appearing as a scenario where a user’s gigabit ethernet drops to 100 Mbps due to an overlooked cable category. A common trap is assuming any Cat cable works for gigabit, but the key distinction is that Cat5 lacks the tighter specifications for 1000BASE-T. To remember this, think: “Cat5 caps at 100—for gigabit, you need an ‘e’ or a ‘6’.”

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

✓

The cable is a Cat5 cable.

Cat5 cable is only rated for 100 Mbps over distances up to 100 meters. Since the run is 75 meters, the cable itself cannot support Gigabit Ethernet (1000BASE-T), which requires at least Cat5e cabling. The switch and NIC being Gigabit-capable confirms the bottleneck is the cable category.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
The cable is a Cat5e patch cable.
Why it's wrong here
Cat5e supports Gigabit Ethernet up to 100 meters, so this would not cause a 100 Mbps limit.
✗
The cable is a Cat6a cable.
Why it's wrong here
Cat6a exceeds Gigabit requirements, so it would not cause a speed drop to 100 Mbps.
✓
The cable is a Cat5 cable.
Why this is correct
Cat5 cable is only rated for 100 Mbps, so using it for a Gigabit connection would limit speed to 100 Mbps.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The cable is a Cat6 cable.
Why it's wrong here
Cat6 supports Gigabit Ethernet, so it would not cause a speed limitation.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates assume any Cat5-style cable (Cat5, Cat5e, Cat6) is sufficient for Gigabit, but only Cat5e and above are certified for 1000BASE-T, and Cat5 is limited to 100 Mbps.

Detailed technical explanation

How to think about this question

1000BASE-T uses all four pairs of the cable and requires Category 5e or higher cabling to meet the tighter crosstalk and return loss specifications. Cat5 cable was designed for 100BASE-TX, which only uses two pairs, so it lacks the necessary performance margin for Gigabit Ethernet, often resulting in the link negotiating down to 100 Mbps. In practice, a marginal Cat5 cable might occasionally link at 1 Gbps but with high error rates, but a 75-meter run reliably forces fallback to 100 Mbps.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A practitioner preparing for the 220-1201 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

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FAQ

Questions learners often ask

What does this 220-1201 question test?

Cabling — This question tests Cabling — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The cable is a Cat5 cable. — Cat5 cable is only rated for 100 Mbps over distances up to 100 meters. Since the run is 75 meters, the cable itself cannot support Gigabit Ethernet (1000BASE-T), which requires at least Cat5e cabling. The switch and NIC being Gigabit-capable confirms the bottleneck is the cable category.

What should I do if I get this 220-1201 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

About these practice questions

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Same concept, more angles

2 more ways this is tested on 220-1201

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A customer reports that their new Gigabit Ethernet connection is only achieving 100 Mbps speeds. The cable run is 75 meters through a drop ceiling and uses a Cat5e cable. What is the most likely cause of the speed limitation?

easy

A.The cable is too long for Cat5e.
✓ B.The cable is actually Cat5, not Cat5e.
C.The cable is shielded and causing interference.
D.The network switch port is faulty.

Why B: Cat5e is rated for Gigabit Ethernet (1000BASE-T) up to 100 meters. However, if the cable is actually Cat5 (not Cat5e), it is only certified for 100 Mbps (100BASE-TX) at that distance. The 75-meter run is within spec for Cat5e, so the most likely cause is that the installed cable is Cat5, which cannot reliably support 1000BASE-T.

Variation 2. A customer reports that their new Gigabit Ethernet connection is only achieving 100 Mbps speeds. The cable run is about 75 meters through a drop ceiling. The technician checks the patch panel and wall jack terminations, which appear correct. What is the most likely cause of the speed issue?

medium

A.The cable run exceeds the maximum length for Gigabit Ethernet.
B.The cable is Cat5e or lower, which cannot support Gigabit Ethernet at that distance.
C.The wall jack is wired for T568B but the patch panel uses T568A.
✓ D.The cable is shielded (STP) and the connectors are unshielded (UTP).

Why D: The most likely cause is that the cable is shielded (STP) but the connectors are unshielded (UTP). When STP cable is used with UTP connectors, the shielding is not properly grounded, leading to signal interference and degradation. This often results in the link falling back to 100 Mbps. The 75-meter run is within the 100-meter limit for Gigabit, and terminations appear correct, so the shield mismatch is the primary suspect.

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