N10-009 Network Troubleshooting Practice Question
A technician is troubleshooting a loss of network connectivity for a single workstation. The workstation has a valid IP address but cannot ping its default gateway. The link lights on both the workstation and the switch are solid. Which of the following should the technician check NEXT?
⚠ Common exam trap
The N10-009 exam often tests the misconception that solid link lights guarantee full Layer 2 connectivity, when in fact they only indicate carrier detect and electrical synchronization, not correct VLAN membership or spanning-tree port state.
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 configuration, such as VLAN assignment
The workstation has a valid IP address and solid link lights, indicating Layer 1 (physical) and Layer 3 (IP configuration) are functional. The inability to ping the default gateway points to a Layer 2 issue, such as the switch port being in the wrong VLAN or having a misconfigured access/trunk setting. Checking the switch port configuration is the logical next step because VLAN mismatches prevent frames from reaching the gateway's subnet.
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 cable integrity with a tester
Why it's wrong here
Solid link lights on both the workstation's NIC and the switch port strongly indicate that the physical Layer 1 connection, including the cable, is intact and functional. A cable integrity tester would confirm this, but its use is less critical when link lights are present, as a faulty cable typically results in no link, an intermittent link, or significant errors. Therefore, while cable integrity is fundamental, it's unlikely the root cause when link lights are solid.
When this WOULD be correct
A technician would check cable integrity with a tester when link lights are off or intermittent, or when there is no link at all, to rule out a faulty cable or termination.
- ✓
The switch port configuration, such as VLAN assignment
Why this is correct
A misconfigured VLAN assignment on the switch port is a common cause of network connectivity loss for a single device, even when physical link lights are solid. If the port is placed in an incorrect VLAN, the workstation will be isolated from its intended network segment and unable to communicate with its default gateway or other devices on its subnet. This Layer 2 misconfiguration effectively prevents IP communication despite a healthy Layer 1 connection.
- ✗
The DNS server settings
Why it's wrong here
DNS server settings are primarily responsible for resolving human-readable domain names into IP addresses. While critical for accessing internet resources by name, DNS is not involved in establishing direct IP connectivity to the default gateway or other devices on the local subnet. If a device cannot reach its gateway by IP, checking DNS settings is premature as the fundamental network path is already broken.
When this WOULD be correct
A technician would check DNS server settings when a workstation has full IP connectivity (can ping gateways and other IPs) but cannot resolve domain names to IP addresses, indicating a DNS resolution failure.
- ✗
The workstation's ARP cache
Why it's wrong here
The workstation's ARP cache maps IP addresses to MAC addresses for local network communication. While a corrupted or stale ARP entry could temporarily disrupt communication with a specific local host, it is rarely the root cause of a complete and persistent loss of network connectivity for a single device. Clearing the ARP cache might offer a temporary fix, but the underlying issue, often a Layer 2 misconfiguration or IP conflict, would likely persist or reoccur.
When this WOULD be correct
A technician would check the ARP cache when a workstation has a valid IP address, can ping other devices on the same subnet, but cannot ping the default gateway, and the switch port configuration is known to be correct. This would help verify if the gateway's MAC address is resolved.
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.
✓The switch port configuration, such as VLAN assignmentCorrect answer▾
Why this is correct
A misconfigured VLAN assignment on the switch port is a common cause of network connectivity loss for a single device, even when physical link lights are solid. If the port is placed in an incorrect VLAN, the workstation will be isolated from its intended network segment and unable to communicate with its default gateway or other devices on its subnet. This Layer 2 misconfiguration effectively prevents IP communication despite a healthy Layer 1 connection.
✗The cable integrity with a testerWrong answer — click to see why▾
Why this is wrong here
The link lights are solid, indicating physical connectivity is present, so cable integrity is not the next logical step. The issue is likely at Layer 2 (switch port configuration) since the workstation has a valid IP but cannot reach the gateway.
★ When this WOULD be the correct answer
A technician would check cable integrity with a tester when link lights are off or intermittent, or when there is no link at all, to rule out a faulty cable or termination.
Why candidates choose this
Candidates often default to checking cables first because physical layer issues are common, but solid link lights already confirm the cable is electrically connected.
✗The DNS server settingsWrong answer — click to see why▾
Why this is wrong here
DNS server settings affect name resolution, not IP-level connectivity to a gateway. Since the workstation has a valid IP but cannot ping the gateway, the issue is at Layer 2 or Layer 3, not DNS.
★ When this WOULD be the correct answer
A technician would check DNS server settings when a workstation has full IP connectivity (can ping gateways and other IPs) but cannot resolve domain names to IP addresses, indicating a DNS resolution failure.
Why candidates choose this
Candidates often confuse 'no internet' with 'no network connectivity' and assume DNS is the cause, especially when the workstation has a valid IP address.
✗The workstation's ARP cacheWrong answer — click to see why▾
Why this is wrong here
The workstation has a valid IP address and link lights are solid, indicating Layer 1 and Layer 3 configuration are likely correct. The inability to ping the gateway despite a valid IP suggests a Layer 2 issue, such as VLAN mismatch, not an ARP cache problem.
★ When this WOULD be the correct answer
A technician would check the ARP cache when a workstation has a valid IP address, can ping other devices on the same subnet, but cannot ping the default gateway, and the switch port configuration is known to be correct. This would help verify if the gateway's MAC address is resolved.
Why candidates choose this
Candidates may think ARP cache corruption could prevent communication with the gateway, but the symptoms (valid IP, solid link lights) point to a Layer 2 issue, not an ARP resolution problem.
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?”
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Related to this question
Learn chapter
Troubleshooting Methodology
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
Default gateway
A default gateway is a network device, typically a router, that acts as the exit point for traffic from a local network to other networks, including the internet.
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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.