N10-009 Network Troubleshooting Practice Question
A user reports that they cannot access any company resources. The technician runs 'ipconfig' and sees that the workstation has an IP address of 169.254.100.25 with a subnet mask of 255.255.0.0. The technician also notices that the 'Default Gateway' is blank. What is the most likely cause?
⚠ Common exam trap
Test-takers frequently confuse APIPA with a link-local address caused by a physical cable issue, but APIPA requires the interface to be in a connected state; a disconnected cable would show no IP address or a 'Media disconnected' status in ipconfig.
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 DHCP server is unavailable or unreachable.
The IP address 169.254.100.25 with a subnet mask of 255.255.0.0 is an Automatic Private IP Addressing (APIPA) address, which Windows assigns when a DHCP client fails to obtain a lease. The blank Default Gateway confirms that no DHCP server responded, so the workstation cannot reach any company resources beyond its local 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 DNS server is not responding.
Why it's wrong here
A non-responsive DNS server primarily impacts name resolution, meaning the workstation would struggle to translate domain names (like companywebsite.com) into IP addresses. However, the process of obtaining an IP address itself is handled by DHCP, which is distinct from DNS. The workstation would still successfully acquire a valid IP address, subnet mask, and default gateway from a functional DHCP server, even if DNS services were unavailable, which would not result in a 169.254.x.x address.
When this WOULD be correct
A user reports they can access internal resources by IP address but not by hostname. The technician checks the workstation's IP configuration and finds a valid DHCP address and default gateway. In this scenario, a non-responsive DNS server is the most likely cause.
- ✓
The DHCP server is unavailable or unreachable.
Why this is correct
When a workstation is configured to obtain an IP address automatically via DHCP, it initiates a discovery process to locate a DHCP server. If the DHCP server is either offline, misconfigured, or unreachable on the network segment, the client will fail to receive a DHCP offer. In such scenarios, the operating system automatically assigns itself an APIPA (Automatic Private IP Addressing) address from the 169.254.0.0/16 range, which allows for limited local network communication but prevents access to external company resources.
- ✗
The workstation has a static IP address configured.
Why it's wrong here
If the workstation had a static IP address configured, it would utilize that specific, manually assigned address for all network communications. APIPA (Automatic Private IP Addressing) is a fallback mechanism exclusively employed by DHCP-enabled clients when they fail to obtain an IP address from a DHCP server and no static IP address has been manually set. Therefore, a static IP configuration would override any attempt to assign an APIPA address, ensuring the workstation uses its designated static IP.
When this WOULD be correct
This option would be correct in a scenario where a user reports no network access, and ipconfig shows a manually configured IP address (e.g., 192.168.1.100) that is not in the correct subnet or conflicts with another device, causing connectivity issues.
- ✗
The network cable is unplugged.
Why it's wrong here
If the network cable were unplugged, the network interface card (NIC) would typically report a 'media disconnected' or 'cable unplugged' status, indicating a complete lack of physical layer connectivity. An APIPA address is only assigned when a physical link is established and active, allowing the DHCP client to attempt communication, but it fails to receive an IP address from a DHCP server. Without an active physical link, the TCP/IP stack would not even initiate the DHCP or APIPA assignment process.
When this WOULD be correct
If a user reports no network access and ipconfig shows 'Media disconnected' with no IP address, the most likely cause is an unplugged or faulty network cable.
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 DHCP server is unavailable or unreachable.Correct answer▾
Why this is correct
When a workstation is configured to obtain an IP address automatically via DHCP, it initiates a discovery process to locate a DHCP server. If the DHCP server is either offline, misconfigured, or unreachable on the network segment, the client will fail to receive a DHCP offer. In such scenarios, the operating system automatically assigns itself an APIPA (Automatic Private IP Addressing) address from the 169.254.0.0/16 range, which allows for limited local network communication but prevents access to external company resources.
✗The DNS server is not responding.Wrong answer — click to see why▾
Why this is wrong here
The IP address 169.254.100.25 is an Automatic Private IP Addressing (APIPA) address, which is assigned when DHCP fails. A non-responsive DNS server would not cause this; it would result in name resolution failures but the workstation would still have a valid DHCP-assigned IP and default gateway.
★ When this WOULD be the correct answer
A user reports they can access internal resources by IP address but not by hostname. The technician checks the workstation's IP configuration and finds a valid DHCP address and default gateway. In this scenario, a non-responsive DNS server is the most likely cause.
Why candidates choose this
Candidates often associate any network connectivity issue with DNS, especially when the symptom is 'cannot access resources.' They may overlook the APIPA address and default gateway being blank, which clearly points to DHCP failure rather than DNS.
✗The workstation has a static IP address configured.Wrong answer — click to see why▾
Why this is wrong here
A static IP address would not result in an APIPA address (169.254.x.x). If a static IP were configured, the workstation would use that address, not self-assign an APIPA address.
★ When this WOULD be the correct answer
This option would be correct in a scenario where a user reports no network access, and ipconfig shows a manually configured IP address (e.g., 192.168.1.100) that is not in the correct subnet or conflicts with another device, causing connectivity issues.
Why candidates choose this
Candidates may think that a static IP could cause misconfiguration, but they overlook that APIPA addresses are only assigned when DHCP fails, not when a static IP is set.
✗The network cable is unplugged.Wrong answer — click to see why▾
Why this is wrong here
An unplugged network cable would result in no IP address or a disconnected status, not an Automatic Private IP Addressing (APIPA) address like 169.254.100.25. The workstation would show 'Media disconnected' in ipconfig.
★ When this WOULD be the correct answer
If a user reports no network access and ipconfig shows 'Media disconnected' with no IP address, the most likely cause is an unplugged or faulty network cable.
Why candidates choose this
Candidates may associate any connectivity issue with a physical layer problem like an unplugged cable, overlooking the specific APIPA address which indicates DHCP failure.
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?”
Visual reference
Quick reference
IPv4 Address Class Summary
| Class | First Octet Range | Default Mask | Networks | Hosts per Network |
|---|---|---|---|---|
| A | 1–126 | /8 (255.0.0.0) | 126 | 16,777,214 |
| B | 128–191 | /16 (255.255.0.0) | 16,384 | 65,534 |
| C | 192–223 | /24 (255.255.255.0) | 2,097,152 | 254 |
| D | 224–239 | N/A | Multicast groups | — |
| E | 240–255 | N/A | Reserved / experimental | — |
127.x.x.x is reserved for loopback. Modern networks use CIDR (classless) rather than classful addressing.
Go deeper
Related to this question
Learn chapter
Default Gateway Configuration Issues
Key term
Automatic Private Internet Protocol Addressing
A fallback method used by a device to automatically assign itself an IP address when it cannot obtain one from a DHCP server.
Key term
DHCP
Dynamic Host Configuration Protocol (DHCP) automatically assigns IP addresses and network settings to devices on a network, so they can communicate without manual configuration.
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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.