N10-009 Network Troubleshooting Practice Question
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?
⚠ Common exam trap
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.
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.
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 an entire network switch is a drastic and costly troubleshooting step that should only be considered after exhausting all other diagnostic possibilities. The absence of a link light is far more commonly attributed to a misconfiguration, such as an administratively disabled port, or a physical layer issue like a faulty cable or transceiver, rather than a complete hardware failure of the switch itself. Premature replacement wastes resources and time without addressing the root cause.
When this WOULD be correct
A question where multiple ports on the same switch fail simultaneously with known good cables and devices, and power cycling the switch does not resolve the issue. In that scenario, the switch hardware may be faulty, making replacement the next logical step.
- ✓
Check if the port is administratively disabled
Why this is correct
When a switch port is administratively disabled, it is intentionally taken offline by a network administrator. This state prevents the port from establishing a physical link, resulting in no link light illumination, regardless of whether a cable is connected or a device is attached. Verifying the port's operational status using CLI commands like 'show interface <interface_id> status' is the crucial first step, and if found disabled, the 'no shutdown' command can reactivate it.
- ✗
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.
When this WOULD be correct
A technician sees that a switch port's link light is on, but the connected device cannot communicate with other devices on the same VLAN. The port is in the correct VLAN, but other ports in that VLAN are also unreachable. In this scenario, checking the VLAN configuration (e.g., VLAN existence, trunk allowed VLANs) would be the next step.
- ✗
Check the speed/duplex settings
Why it's wrong here
Incorrect speed or duplex settings between a switch port and a connected device typically manifest as a link light being illuminated, indicating a physical connection, but with significant performance issues, packet loss, or error counters incrementing rapidly. A complete absence of a link light, however, signifies that a physical link cannot be established at all, which is a lower-layer problem than a speed/duplex mismatch. This points towards an administratively disabled port, a faulty cable, or a hardware issue with the port itself.
When this WOULD be correct
A technician sees intermittent connectivity or high error counts on a link, but the link light is lit. The cable and port are known good, and the question asks for the next step to resolve performance issues. In that case, checking speed/duplex settings would be appropriate.
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.
✓Check if the port is administratively disabledCorrect answer▾
Why this is correct
When a switch port is administratively disabled, it is intentionally taken offline by a network administrator. This state prevents the port from establishing a physical link, resulting in no link light illumination, regardless of whether a cable is connected or a device is attached. Verifying the port's operational status using CLI commands like 'show interface <interface_id> status' is the crucial first step, and if found disabled, the 'no shutdown' command can reactivate it.
✗Replace the switchWrong answer — click to see why▾
Why this is wrong here
Replacing the switch is an extreme and premature action; the issue is likely isolated to a single port, and the switch itself is probably functional. The technician should first check for administrative disablement before considering hardware replacement.
★ When this WOULD be the correct answer
A question where multiple ports on the same switch fail simultaneously with known good cables and devices, and power cycling the switch does not resolve the issue. In that scenario, the switch hardware may be faulty, making replacement the next logical step.
Why candidates choose this
Candidates may jump to replacing hardware when a link light is off, assuming physical failure, without systematically troubleshooting software or configuration causes first.
✗Check the VLAN configurationWrong answer — click to see why▾
Why this is wrong here
The link light not lit indicates a Layer 1 or Layer 2 connectivity issue, not a VLAN mismatch. VLAN configuration problems typically allow the link to come up but prevent traffic forwarding, so checking VLAN config is premature before verifying basic port status.
★ When this WOULD be the correct answer
A technician sees that a switch port's link light is on, but the connected device cannot communicate with other devices on the same VLAN. The port is in the correct VLAN, but other ports in that VLAN are also unreachable. In this scenario, checking the VLAN configuration (e.g., VLAN existence, trunk allowed VLANs) would be the next step.
Why candidates choose this
Candidates may confuse symptoms of VLAN misconfiguration (no connectivity) with physical link issues, or they might skip basic troubleshooting steps and jump to more complex Layer 2 checks.
✗Check the speed/duplex settingsWrong answer — click to see why▾
Why this is wrong here
Speed/duplex mismatches typically cause packet errors or slow performance, not a completely unlit link light. The link light not being lit indicates a Layer 1 issue (no electrical signal), which is not resolved by checking speed/duplex settings.
★ When this WOULD be the correct answer
A technician sees intermittent connectivity or high error counts on a link, but the link light is lit. The cable and port are known good, and the question asks for the next step to resolve performance issues. In that case, checking speed/duplex settings would be appropriate.
Why candidates choose this
Candidates may confuse symptoms of speed/duplex mismatch (like high errors or slow performance) with a complete loss of link, or they may think that mismatch can prevent the link from coming up entirely.
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?”
Go deeper
Related to this question
Learn chapter
Troubleshoot: Cable and Physical Layer
Key term
Switch
A switch is a networking device that connects devices on a local area network and uses MAC addresses to forward data only to the intended recipient.
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.