Question 163 of 464
N10-009 Networking Concepts Practice Question
A network engineer is troubleshooting connectivity issues between two data center switches that are configured to support jumbo frames with an MTU of 9000. The link is a 10 Gigabit Ethernet fiber connection. Large file transfers fail, but small transfers succeed. What is the most likely cause?
⚠ Common exam trap
Many candidates assume a physical layer issue (like a bad cable or transceiver) when the symptom is selective failure based on packet size, but the real cause is an MTU mismatch, which is a Layer 2 configuration problem.
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
✓
C
The most likely cause is that an intermediate device (such as a router or another switch) along the Layer 2 path is not configured for jumbo frames and has a standard MTU of 1500. Since both end switches support an MTU of 9000, large frames are sent but are dropped when they reach the intermediate device that cannot handle them. Small frames (≤1500 bytes) pass through successfully because they fit within the standard MTU.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A
Why it's wrong here
10 Gigabit Ethernet is widely supported and not the cause of this specific issue.
When this WOULD be correct
Option A would be correct in a scenario where one switch is configured for jumbo frames (MTU 9000) and the other is set to the default MTU (1500), causing large frame fragmentation or drops.
- ✗
B
Why it's wrong here
While a faulty fiber cable could cause general failures, the pattern of small transfers working and large transfers failing points to an MTU issue.
When this WOULD be correct
If the question described intermittent connectivity or errors on a fiber link with both small and large transfers failing, then fiber attenuation or dirty connectors could be the cause, making B correct.
- ✓
C
Why this is correct
An intermediate device with a standard MTU will drop large frames, causing jumbo frame traffic to fail.
- ✗
D
Why it's wrong here
TCP window size affects throughput but not the ability to transfer large files at all; small transfers would also fail if window size were severely misconfigured.
When this WOULD be correct
In a scenario where a network engineer is troubleshooting intermittent connectivity and finds that disabling jumbo frames resolves the issue, option D (if it were 'Disable jumbo frames on both switches') would be correct to restore connectivity at the cost of performance.
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 N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓CCorrect answer▾
Why this is correct
An intermediate device with a standard MTU will drop large frames, causing jumbo frame traffic to fail.
✗AWrong answer — click to see why▾
Why this is wrong here
Option A is not a valid answer choice in this question; the actual options are not provided, but assuming 'A' refers to a common distractor like 'MTU mismatch', that would be incorrect because both switches are configured for jumbo frames with MTU 9000, so MTU mismatch is not the issue.
★ When this WOULD be the correct answer
Option A would be correct in a scenario where one switch is configured for jumbo frames (MTU 9000) and the other is set to the default MTU (1500), causing large frame fragmentation or drops.
Why candidates choose this
Candidates often default to 'MTU mismatch' as a common cause of large file transfer failures, without verifying that both devices are consistently configured.
✗BWrong answer — click to see why▾
Why this is wrong here
Option B is not specified, but assuming it refers to a common incorrect cause like 'CRC errors' or 'fiber attenuation', these would not selectively affect large transfers while allowing small ones; jumbo frame issues typically stem from MTU mismatch or switch configuration.
★ When this WOULD be the correct answer
If the question described intermittent connectivity or errors on a fiber link with both small and large transfers failing, then fiber attenuation or dirty connectors could be the cause, making B correct.
Why candidates choose this
Candidates may confuse general physical layer issues with MTU-specific problems, or they might recall that fiber problems can cause packet loss, but fail to recognize that MTU mismatch only impacts large frames.
✗DWrong answer — click to see why▾
Why this is wrong here
Option D is not provided in the question, so it cannot be analyzed. The correct answer is C, which likely refers to a mismatch in MTU settings or jumbo frame configuration across the path, causing large frames to be dropped.
★ When this WOULD be the correct answer
In a scenario where a network engineer is troubleshooting intermittent connectivity and finds that disabling jumbo frames resolves the issue, option D (if it were 'Disable jumbo frames on both switches') would be correct to restore connectivity at the cost of performance.
Why candidates choose this
Without the actual text of option D, it's impossible to determine why it might be tempting. Typically, wrong options in such questions might suggest incorrect causes like faulty cables or duplex mismatches, which candidates might choose due to common troubleshooting experience.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Last reviewed: Jun 11, 2026
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.
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