Troubleshooting Duplex Mismatch for Slow Network
A technician is troubleshooting a desktop computer that intermittently loses network connectivity for several minutes at a time. During the outage, the link light on the NIC remains on and flickers. The technician has already replaced the Ethernet cable and the NIC. The computer is connected to a managed switch port configured for auto-negotiation. Which of the following should the technician check NEXT?
⚠ Common exam trap
The trap here is that candidates see the link light on and assume the physical layer is fine, so they jump to higher-layer causes like IP conflicts or firewall rules, missing that a duplex mismatch can cause intermittent outages while the link light remains active.
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 switch port for a duplex mismatch with the NIC
The link light remaining on and flickering during an outage indicates Layer 1 (physical) and Layer 2 (data link) connectivity are present, but the issue is likely a duplex mismatch. When one side of a link is set to full-duplex and the other to half-duplex (often due to failed auto-negotiation), collisions and frame errors cause intermittent connectivity loss lasting minutes. Since the cable and NIC have already been replaced, the next logical step is to check the switch port's duplex setting against the NIC's negotiated duplex.
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 computer's IP address for a static conflict
Why it's wrong here
An IP address conflict is detected by the operating system via ARP and usually triggers a warning message and immediate, continuous loss of connectivity to the conflicting host; it does not cause intermittent, multi-minute outages while the NIC and switch maintain link. Because the conflict is at Layer 3, the switch port would still forward frames normally, and the failure would be persistent until the IP is changed, not cyclical in nature.
When this WOULD be correct
This would be correct if the question described a computer that cannot connect to the network at all or has an IP address conflict warning, and the link light is off or shows no activity. For example: 'A user reports that their computer has no network access. The link light is off. The technician checks the cable and finds it secure. What should the technician check next?'
- ✓
The switch port for a duplex mismatch with the NIC
Why this is correct
A duplex mismatch is a common cause of intermittent connectivity. The switch and NIC may both auto-negotiate, but if one is forced to a specific setting, errors occur. Checking and matching duplex settings is the next logical step.
- ✗
The operating system's firewall settings
Why it's wrong here
Operating system firewall rules function at Layer 4 and are typically static; if a rule blocks a port or application, it drops all matching traffic consistently, not in a pattern that lasts only minutes and then recovers on its own. The symptom of the link light remaining lit and connectivity returning spontaneously points to a Layer 1/2 physical or data-link problem, such as a duplex mismatch, rather than a policy-based filter that would act deterministically.
When this WOULD be correct
A user reports that a specific application cannot connect to the internet, but other applications work fine. The technician should check the OS firewall settings to ensure the application is not blocked.
- ✗
The network driver version for compatibility
Why it's wrong here
An outdated or incompatible NIC driver typically manifests as persistent failures—like the adapter not enumerating, frequent system crashes, or complete loss of connectivity—rather than brief, repeating outages with the link light still active. The regular pattern of connectivity dropping and returning in minutes without a driver update or system restart strongly indicates a physical-layer negotiation problem; a duplex mismatch, not a software version issue, produces exactly this signature of late collisions and CRC errors.
When this WOULD be correct
A technician is troubleshooting a desktop that cannot connect to the network after a driver update. The link light is off or blinking erratically, and the NIC is detected in Device Manager with an error. In this scenario, checking the network driver version for compatibility would be the next step.
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 220-1101 exam frequently reuses these exact scenarios with slightly different constraints.
✓The switch port for a duplex mismatch with the NICCorrect answer▾
Why this is correct
A duplex mismatch is a common cause of intermittent connectivity. The switch and NIC may both auto-negotiate, but if one is forced to a specific setting, errors occur. Checking and matching duplex settings is the next logical step.
✗The computer's IP address for a static conflictWrong answer — click to see why▾
Why this is wrong here
A static IP conflict would cause persistent connectivity issues, not intermittent outages with the link light remaining on and flickering. The symptoms point to a layer 1/2 issue, not an IP addressing problem.
★ When this WOULD be the correct answer
This would be correct if the question described a computer that cannot connect to the network at all or has an IP address conflict warning, and the link light is off or shows no activity. For example: 'A user reports that their computer has no network access. The link light is off. The technician checks the cable and finds it secure. What should the technician check next?'
Why candidates choose this
Candidates may think IP conflicts cause intermittent issues, but they typically cause persistent problems or complete loss of connectivity, not the specific pattern described.
✗The operating system's firewall settingsWrong answer — click to see why▾
Why this is wrong here
Intermittent connectivity with link light on suggests a layer 1/2 issue, not a firewall blocking traffic. Firewall rules typically cause consistent, not intermittent, outages.
★ When this WOULD be the correct answer
A user reports that a specific application cannot connect to the internet, but other applications work fine. The technician should check the OS firewall settings to ensure the application is not blocked.
Why candidates choose this
Candidates may assume any connectivity issue is due to security software, especially after replacing hardware, without considering that firewall problems are usually consistent, not intermittent.
✗The network driver version for compatibilityWrong answer — click to see why▾
Why this is wrong here
The network driver version is unlikely to cause intermittent connectivity with the link light remaining on and flickering, as driver issues typically cause complete failure or persistent problems, not intermittent outages with active link lights.
★ When this WOULD be the correct answer
A technician is troubleshooting a desktop that cannot connect to the network after a driver update. The link light is off or blinking erratically, and the NIC is detected in Device Manager with an error. In this scenario, checking the network driver version for compatibility would be the next step.
Why candidates choose this
Candidates may think driver issues can cause intermittent problems, but the symptom of a flickering link light during outages points to a physical or configuration issue, not a driver problem.
Analysis generated from the official 220-1101blueprint 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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 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 220-1101 exam.