- A
The cable run exceeds the maximum length for Cat6a.
Why wrong: Cat6a supports up to 100 meters, so 90 meters is within limits.
- B
The switch port is configured for 100 Mbps only.
Why wrong: This is possible but less likely if the certifier test passed; the issue is more likely physical.
- C
The patch cables are Cat5e instead of Cat6a.
Using Cat5e patch cables can bottleneck the link to 100 Mbps, even if the permanent link is Cat6a.
- D
The cable is terminated in T568A instead of T568B.
Why wrong: Both standards work as long as both ends match; this would not cause a speed drop.
Question 637 of 1,020
Why Does Cat6a Pass Certification but Only Run at 100 Mbps?
This 220-1201 practice question tests your understanding of cabling. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 Cat6a installation passes a cable certifier test but the link only negotiates at 100 Mbps. The cable run is 90 meters and uses standard T568B terminations. What is the most likely cause of 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.
Quick Answer
The answer is the patch cables are Cat5e instead of Cat6a. This is the most likely cause because a cable certifier validates the permanent link—the in-wall cabling—against Category 6a standards, but it does not test the patch cables connecting the device to the wall jack. If those patch cables are only rated for Cat5e, they cannot reliably support frequencies above 100 MHz, which forces the link to fall back to 100 Mbps even though the permanent run passes certification. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding that certification and actual speed negotiation are separate processes; a common trap is to assume a passing certifier result guarantees full gigabit performance. Remember the memory tip: “The permanent link may pass, but the patch cable is the bottleneck in the glass.” Always verify the entire end-to-end path, not just the in-wall run.
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 patch cables are Cat5e instead of Cat6a.
The cable certifier passes because the physical layer (Cat6a cabling) meets specifications for signal integrity and crosstalk. However, if the patch cables connecting the equipment to the structured cabling are Cat5e, they may not support the higher frequencies required for 1000BASE-T (up to 100 MHz for Cat5e vs. 500 MHz for Cat6a). This can cause the link to fall back to 100BASE-TX, which operates at lower frequencies and is more tolerant of the reduced performance of Cat5e patch cables.
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 run exceeds the maximum length for Cat6a.
Why it's wrong here
Cat6a supports up to 100 meters, so 90 meters is within limits.
- ✗
The switch port is configured for 100 Mbps only.
Why it's wrong here
This is possible but less likely if the certifier test passed; the issue is more likely physical.
- ✓
The patch cables are Cat5e instead of Cat6a.
Why this is correct
Using Cat5e patch cables can bottleneck the link to 100 Mbps, even if the permanent link is Cat6a.
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 terminated in T568A instead of T568B.
Why it's wrong here
Both standards work as long as both ends match; this would not cause a speed drop.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a passing certifier result guarantees full link speed, but the certifier tests the permanent link only, not the patch cables, so the issue is likely in the patch cords.
Detailed technical explanation
How to think about this question
Under the hood, 1000BASE-T uses all four pairs and requires a signal-to-noise ratio that is sensitive to return loss and near-end crosstalk (NEXT). Cat5e patch cables have higher insertion loss and lower NEXT margins at higher frequencies, which can cause the auto-negotiation process to fail to establish a Gigabit link, forcing a fallback to 100BASE-TX (which uses only two pairs and is less demanding). In real-world scenarios, using Cat6a patch cables with Cat6a structured cabling ensures the entire channel meets the 500 MHz bandwidth requirement for 10GBASE-T, but even for 1000BASE-T, mismatched patch cables can degrade performance.
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.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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 patch cables are Cat5e instead of Cat6a. — The cable certifier passes because the physical layer (Cat6a cabling) meets specifications for signal integrity and crosstalk. However, if the patch cables connecting the equipment to the structured cabling are Cat5e, they may not support the higher frequencies required for 1000BASE-T (up to 100 MHz for Cat5e vs. 500 MHz for Cat6a). This can cause the link to fall back to 100BASE-TX, which operates at lower frequencies and is more tolerant of the reduced performance of Cat5e patch cables.
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.
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Last reviewed: Jul 4, 2026
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