- A
The route table on the default gateway
Why wrong: Routing issues typically affect connectivity between subnets, not local intermittent performance. The workstation can still communicate locally, so routing is likely not the cause.
- B
The duplex and speed settings on both ends
Autonegotiation can fail, resulting in a duplex mismatch where one side runs at half-duplex and the other at full-duplex. This causes collisions and retransmissions, leading to intermittent connectivity and slow transfers.
- C
The DNS server configuration
Why wrong: DNS issues would cause name resolution failures, not intermittent connectivity or slow file transfers. File transfers use IP addresses after initial resolution.
- D
The MAC address filtering on the switch
Why wrong: MAC filtering would either block traffic completely or allow it; it does not cause intermittent performance issues. The workstation is connected, so filtering is not the problem.
N10-009 Network Troubleshooting Practice Question
This N10-009 practice question tests your understanding of network troubleshooting. 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 technician is troubleshooting a workstation that is experiencing intermittent connectivity and slow file transfers. The technician has confirmed that the patch cable passes a cable tester, the switch port is not error-disabled, and the workstation's NIC is configured for autonegotiation. The switch port is also set to autonegotiate. Which of the following should the technician check next?
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 duplex and speed settings on both ends
Option B is correct because intermittent connectivity and slow file transfers, despite a passing cable test and autonegotiation on both ends, strongly indicate a duplex mismatch. When both sides are set to autonegotiate but one side fails to negotiate correctly (e.g., due to a faulty NIC or switch port), they may fall back to half-duplex while the other remains full-duplex, causing collisions, CRC errors, and retransmissions. The technician should verify the actual negotiated duplex and speed on both the workstation NIC and the switch port using commands like 'show interfaces' or NIC driver properties.
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 route table on the default gateway
Why it's wrong here
Routing issues typically affect connectivity between subnets, not local intermittent performance. The workstation can still communicate locally, so routing is likely not the cause.
- ✓
The duplex and speed settings on both ends
Why this is correct
Autonegotiation can fail, resulting in a duplex mismatch where one side runs at half-duplex and the other at full-duplex. This causes collisions and retransmissions, leading to intermittent connectivity and slow transfers.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The DNS server configuration
Why it's wrong here
DNS issues would cause name resolution failures, not intermittent connectivity or slow file transfers. File transfers use IP addresses after initial resolution.
- ✗
The MAC address filtering on the switch
Why it's wrong here
MAC filtering would either block traffic completely or allow it; it does not cause intermittent performance issues. The workstation is connected, so filtering is not the problem.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that if a cable tester passes and autonegotiation is enabled on both ends, the link must be fully functional, but the trap is that autonegotiation can fail silently, resulting in a duplex mismatch that causes the exact symptoms described.
Detailed technical explanation
How to think about this question
Autonegotiation, defined by IEEE 802.3, uses Fast Link Pulses (FLPs) to exchange capabilities; if one side fails to receive FLPs (e.g., due to a marginal cable or port), it may default to half-duplex while the other remains full-duplex. This mismatch causes late collisions and frame errors at the half-duplex side, drastically reducing throughput. In real-world scenarios, a technician might see high CRC errors on the switch interface, confirming the mismatch even when the cable tester passes.
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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this N10-009 question test?
Network Troubleshooting — This question tests Network Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The duplex and speed settings on both ends — Option B is correct because intermittent connectivity and slow file transfers, despite a passing cable test and autonegotiation on both ends, strongly indicate a duplex mismatch. When both sides are set to autonegotiate but one side fails to negotiate correctly (e.g., due to a faulty NIC or switch port), they may fall back to half-duplex while the other remains full-duplex, causing collisions, CRC errors, and retransmissions. The technician should verify the actual negotiated duplex and speed on both the workstation NIC and the switch port using commands like 'show interfaces' or NIC driver properties.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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