Question 772 of 1,020

Network Configuration Concepts →hardMultiple ChoiceObjective-mapped

How Duplex Mismatch Between Switch and NIC Causes High Latency

This 220-1201 practice question tests your understanding of network configuration concepts. 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 technician is troubleshooting a slow network connection for a user. The user's computer has an IP address of 192.168.1.100, subnet mask 255.255.255.0, and default gateway 192.168.1.1. The technician runs a ping to the gateway and gets replies with times around 2ms. However, pinging a server at 192.168.1.200 results in times over 500ms. The technician checks the switch and finds that the port for the user's computer is set to 10 Mbps half-duplex, while the computer's NIC is set to auto-negotiation. What is the most likely cause of the high latency?

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 server at 192.168.1.200 is overloaded.
Why wrong: If the server were overloaded, pinging it might show high latency, but the issue is specific to this user's connection, not the server itself.
B
The user's computer has a faulty network cable.
Why wrong: A faulty cable could cause errors, but the ping to the gateway is fine (2ms), suggesting the cable is not the primary issue.
C
There is a duplex mismatch between the switch port and the NIC.
The switch port is set to 10 Mbps half-duplex, while the NIC is auto-negotiating. This often results in a mismatch where the NIC runs at half-duplex, causing collisions and high latency.
D
The default gateway is misconfigured.
Why wrong: The ping to the gateway is fast, so the gateway is working correctly. The issue is with the path to the server, likely due to the duplex mismatch.

Full breakdown with real-world context →

Quick Answer

The answer is a duplex mismatch between the switch port and the NIC. This occurs because the switch port is manually locked to 10 Mbps half-duplex, while the NIC is set to auto-negotiation; when one side is fixed and the other is set to auto, the auto-negotiation process fails, forcing the NIC to fall back to half-duplex as well, but often at a mismatched speed, causing excessive collisions and retransmissions that spike latency. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of how slow network performance can stem from physical layer misconfigurations rather than IP issues—notice that pinging the local gateway is fast, but crossing the switch to another device is slow, a classic sign of duplex mismatch. A common trap is to blame the IP configuration or a bad cable, but the real culprit is the half-duplex bottleneck. Memory tip: “Half-duplex is half the conversation—one talks, one waits, and latency accumulates.”

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

✓

There is a duplex mismatch between the switch port and the NIC.

The switch port is manually configured to 10 Mbps half-duplex, while the computer's NIC is set to auto-negotiation. When one side is hard-coded and the other is set to auto-negotiation, the auto-negotiating side will detect the speed (10 Mbps) but fall back to half-duplex as a default, resulting in a duplex mismatch. This mismatch causes frame collisions and retransmissions, dramatically increasing latency (500+ ms) while local pings to the gateway remain low because the gateway is on the same switch and not affected by the mismatch.

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 server at 192.168.1.200 is overloaded.
Why it's wrong here
If the server were overloaded, pinging it might show high latency, but the issue is specific to this user's connection, not the server itself.
✗
The user's computer has a faulty network cable.
Why it's wrong here
A faulty cable could cause errors, but the ping to the gateway is fine (2ms), suggesting the cable is not the primary issue.
✓
There is a duplex mismatch between the switch port and the NIC.
Why this is correct
The switch port is set to 10 Mbps half-duplex, while the NIC is auto-negotiating. This often results in a mismatch where the NIC runs at half-duplex, causing collisions and high latency.
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 default gateway is misconfigured.
Why it's wrong here
The ping to the gateway is fast, so the gateway is working correctly. The issue is with the path to the server, likely due to the duplex mismatch.

Common exam traps

Common exam trap: answer the scenario, not the keyword

A common trap in CompTIA A+ is that a duplex mismatch causes high latency but not necessarily packet loss, leading candidates to incorrectly suspect a faulty cable or overloaded server, when the real issue is the mismatch between manual and auto-negotiation settings.

Trap categories for this question

Command / output trap
If the server were overloaded, pinging it might show high latency, but the issue is specific to this user's connection, not the server itself.

Detailed technical explanation

How to think about this question

When a duplex mismatch occurs, the half-duplex side waits for a clear channel before transmitting, while the full-duplex side transmits without checking, causing collisions on the half-duplex side. The half-duplex side then backs off and retransmits, introducing delays that can exceed 500 ms. This scenario is common when one device is hard-coded (e.g., for legacy compatibility) and the other uses auto-negotiation, as per IEEE 802.3 Clause 28, which mandates that auto-negotiation defaults to half-duplex if speed is detected but duplex cannot be negotiated.

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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.

Visual reference

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?

Network Configuration Concepts — This question tests Network Configuration Concepts — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: There is a duplex mismatch between the switch port and the NIC. — The switch port is manually configured to 10 Mbps half-duplex, while the computer's NIC is set to auto-negotiation. When one side is hard-coded and the other is set to auto-negotiation, the auto-negotiating side will detect the speed (10 Mbps) but fall back to half-duplex as a default, resulting in a duplex mismatch. This mismatch causes frame collisions and retransmissions, dramatically increasing latency (500+ ms) while local pings to the gateway remain low because the gateway is on the same switch and not affected by the mismatch.

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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