- A
Replace the switch
Why wrong: Replacing the switch without first verifying the port configuration is unnecessary. The issue is likely a disabled port, not a hardware failure.
- B
Check if the port is administratively disabled
A port that is administratively down will not light up. Use the command 'show interface' or 'show interface status' to verify and then use 'no shutdown' to enable it.
- C
Check the VLAN configuration
Why wrong: While VLAN mismatch can cause issues, the lack of link light typically indicates a physical or administrative issue, not a VLAN problem. VLAN issues usually result in link lights being on but no data flow.
- D
Check the speed/duplex settings
Why wrong: Speed/duplex mismatches usually cause a link light to be on but with errors. No link light at all suggests the port is disabled or there is a physical fault.
Quick Answer
The correct next step is to check if the switch port is administratively disabled, as a link light not lit on a switch port despite a known good cable and an active device almost always points to the port being in a shutdown state. This occurs because the interface has been configured with the 'shutdown' command at the command line, which prevents the port from sending or receiving electrical signals to negotiate a link at Layer 1. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to differentiate between physical cable faults and configuration issues—a common trap is to immediately replace the cable or device, when the real culprit is the port being administratively down. To confirm, use 'show interfaces status' to look for the "administratively down" flag. Memory tip: "No light? Check the CLI—shutdown kills the link, not the cable."
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 sees that the link light on a switch port is not lit, even though the cable is connected to an active device. The port has been tested with a known good cable. Which of the following should the technician do 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
Check if the port is administratively disabled
When a link light is off despite a known good cable and an active device, the most likely cause is that the switch port is administratively disabled (shutdown). This is a common Layer 1/2 issue where the interface is configured with the 'shutdown' command, preventing the port from negotiating a link. Checking the interface status with 'show interfaces status' or 'show interfaces [interface]' will confirm if the port is in an 'administratively down' state.
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.
- ✗
Replace the switch
Why it's wrong here
Replacing the switch without first verifying the port configuration is unnecessary. The issue is likely a disabled port, not a hardware failure.
- ✓
Check if the port is administratively disabled
Why this is correct
A port that is administratively down will not light up. Use the command 'show interface' or 'show interface status' to verify and then use 'no shutdown' to enable it.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Check the VLAN configuration
Why it's wrong here
While VLAN mismatch can cause issues, the lack of link light typically indicates a physical or administrative issue, not a VLAN problem. VLAN issues usually result in link lights being on but no data flow.
- ✗
Check the speed/duplex settings
Why it's wrong here
Speed/duplex mismatches usually cause a link light to be on but with errors. No link light at all suggests the port is disabled or there is a physical fault.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often jump to VLAN or hardware failure (replace the switch) because they forget that an administratively down port is a common Layer 1 misconfiguration that completely prevents link establishment, even with a good cable and active device.
Detailed technical explanation
How to think about this question
The link light indicates successful electrical or optical signal negotiation at the Physical layer, governed by auto-negotiation (IEEE 802.3ab for copper, 1000BASE-T). An administratively disabled port sends no link pulses, so the device never sees a carrier. In real-world scenarios, ports are often left in 'shutdown' after maintenance or security hardening, and a simple 'no shutdown' command resolves the issue without any hardware changes.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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 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: Check if the port is administratively disabled — When a link light is off despite a known good cable and an active device, the most likely cause is that the switch port is administratively disabled (shutdown). This is a common Layer 1/2 issue where the interface is configured with the 'shutdown' command, preventing the port from negotiating a link. Checking the interface status with 'show interfaces status' or 'show interfaces [interface]' will confirm if the port is in an 'administratively down' state.
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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