This N10-009 practice question tests your understanding of networking 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 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?
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.
Why wrong: 10 Gigabit Ethernet is widely supported and not the cause of this specific issue.
B
B
Why wrong: While a faulty fiber cable could cause general failures, the pattern of small transfers working and large transfers failing points to an MTU issue.
C
C
An intermediate device with a standard MTU will drop large frames, causing jumbo frame traffic to fail.
D
D
Why wrong: 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.
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 the MTU mismatch is causing large frames to be dropped. Jumbo frames of 9000 bytes require a consistent MTU across the entire Layer 2 path. If one switch is configured for 9000 and the other for the standard 1500, large frames will be silently discarded because the receiving switch cannot reassemble them. Small transfers succeed because they fit within the standard MTU.
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.
✗
A
Why it's wrong here
10 Gigabit Ethernet is widely supported and not the cause of this specific issue.
✗
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.
✓
C
Why this is correct
An intermediate device with a standard MTU will drop large frames, causing jumbo frame traffic to fail.
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.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often 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.
Detailed technical explanation
How to think about this question
Jumbo frames are Ethernet frames with a payload larger than 1500 bytes, up to 9000 bytes. The MTU is configured on each interface; if a switch receives a frame larger than its MTU, it drops it silently (no ICMP notification in Layer 2). In a data center, jumbo frames reduce CPU overhead by enabling larger data chunks per packet, but all devices in the path must support and be configured for the same MTU. A common real-world scenario is a storage network (e.g., iSCSI or NFS) where jumbo frames improve throughput, but a misconfigured switch causes partial failures.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Networking Concepts — This question tests Networking Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: C — The most likely cause is that the MTU mismatch is causing large frames to be dropped. Jumbo frames of 9000 bytes require a consistent MTU across the entire Layer 2 path. If one switch is configured for 9000 and the other for the standard 1500, large frames will be silently discarded because the receiving switch cannot reassemble them. Small transfers succeed because they fit within the standard MTU.
What should I do if I get this N10-009 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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Question Discussion
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