The correct answer is that the DHCP server is unreachable. When a Windows client is configured for automatic IP addressing but cannot contact a DHCP server, it self-assigns an APIPA address from the 169.254.0.0/16 range, such as 169.254.15.7 with a 255.255.0.0 subnet mask. This link-local address allows only local subnet communication, which explains why the user cannot access any network resources like file servers or the internet. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of the DHCP lease process and APIPA as a fallback mechanism; a common trap is to suspect a faulty network cable or incorrect subnet mask, but the 169.254 address specifically points to a missing DHCP server. A helpful memory tip is to think of 169.254 as “I’m stuck, no DHCP” — the first three octets sound like “I’m sick, no help.”
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 user's workstation shows an IP address of 169.254.15.7 with a subnet mask of 255.255.0.0. The user cannot access any network resources. Which of the following is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 unreachable
The IP address 169.254.15.7 with a /16 subnet mask is an Automatic Private IP Addressing (APIPA) address, assigned by Windows when a DHCP client fails to obtain a lease. This indicates the workstation cannot reach a DHCP server, so the most likely cause is that the DHCP server is unreachable.
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.
✗
The DNS server is not responding
Why it's wrong here
A DNS failure would not cause the workstation to obtain an APIPA address; the DHCP process would still complete successfully.
✓
The DHCP server is unreachable
Why this is correct
When a DHCP client cannot contact a DHCP server, it auto-configures with an APIPA address in the 169.254.0.0/16 range.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The subnet mask is incorrect
Why it's wrong here
An incorrect subnet mask would be assigned by DHCP; the APIPA address indicates DHCP failure, not a misconfiguration.
✗
The default gateway is down
Why it's wrong here
A default gateway issue would not prevent DHCP lease acquisition; the workstation would still receive a proper IP address from DHCP.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse APIPA with a DNS or gateway issue, but APIPA specifically indicates DHCP failure, not a problem with higher-layer services or routing.
Detailed technical explanation
How to think about this question
APIPA is defined in RFC 3927 and uses the 169.254.0.0/16 block, with the host automatically selecting a link-local address via ARP probing to avoid conflicts. This mechanism only activates when a DHCP Discover broadcast times out (typically after 4 retries over ~21 seconds), ensuring the host can still communicate on the local link even without a DHCP server.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
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: The DHCP server is unreachable — The IP address 169.254.15.7 with a /16 subnet mask is an Automatic Private IP Addressing (APIPA) address, assigned by Windows when a DHCP client fails to obtain a lease. This indicates the workstation cannot reach a DHCP server, so the most likely cause is that the DHCP server is unreachable.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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