- A
The DNS server is not responding
Why wrong: DNS issues would affect name resolution but not IP address assignment. The client would still get a valid DHCP address, not an APIPA address.
- B
The DHCP server is unavailable or the request is not reaching it
APIPA occurs when DHCP fails. Possible causes include DHCP server down, a misconfigured DHCP relay, or a VLAN mismatch preventing DHCP broadcast from reaching the server.
- C
The subnet mask is incorrect
Why wrong: The subnet mask of 255.255.0.0 is standard for APIPA. The problem is not the mask itself but the entire IP range being non-routable.
- D
The switch port has port security enabled that has blocked the device
Why wrong: If port security blocked the device, it would likely be disconnected completely from the switch, not obtain an APIPA address. The client has Layer 2 connectivity (associated to Wi-Fi).
Quick Answer
The answer is that the DHCP server is unavailable or the request is not reaching it. This is correct because the 169.254.x.x address, specifically 169.254.25.100 with a 255.255.0.0 subnet mask, is an Automatic Private IP Addressing (APIPA) address assigned by Windows when a DHCP discover/offer/request/ack sequence fails. Since the user can connect to Wi-Fi but cannot access any network resources, the link-local address cannot route beyond the local subnet, confirming the DHCP server is unreachable. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to recognize APIPA as a fallback mechanism and differentiate it from a static IP misconfiguration—a common trap where candidates blame DNS or gateway issues. Remember the memory tip: “169.254 means DHCP is a stranger,” so when you see that address, always suspect the DHCP server first.
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 reports that they can connect to the corporate Wi-Fi network but cannot access any network resources including the intranet and internet. The IP configuration shows an IP address of 169.254.25.100 with a subnet mask of 255.255.0.0. What 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 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 the request is not reaching it
The IP address 169.254.25.100 with a subnet mask of 255.255.0.0 is an Automatic Private IP Addressing (APIPA) address, which is assigned by the operating system when a DHCP server is unavailable or the DHCP request fails. Since the user can connect to Wi-Fi but cannot access any network resources, the most likely cause is that the DHCP server is not responding or the DHCP discover/offer/request/ack sequence is failing, leaving the device with a link-local address that cannot route to the corporate network or internet.
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
- ✓
The DHCP server is unavailable or the request is not reaching it
Why this is correct
APIPA occurs when DHCP fails. Possible causes include DHCP server down, a misconfigured DHCP relay, or a VLAN mismatch preventing DHCP broadcast from reaching the server.
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
The subnet mask of 255.255.0.0 is standard for APIPA. The problem is not the mask itself but the entire IP range being non-routable.
- ✗
The switch port has port security enabled that has blocked the device
Why it's wrong here
If port security blocked the device, it would likely be disconnected completely from the switch, not obtain an APIPA address. The client has Layer 2 connectivity (associated to Wi-Fi).
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse APIPA with a DNS failure, but the 169.254.x.x address is a definitive indicator of DHCP failure, not a name resolution problem.
Detailed technical explanation
How to think about this question
APIPA uses the 169.254.0.0/16 range (169.254.1.0 to 169.254.254.255) and is defined in RFC 3927; the operating system assigns this address after four DHCP discover attempts fail (each with a timeout of 1 second, then 2, 4, and 8 seconds). In a real-world scenario, a misconfigured DHCP relay agent (ip helper-address) on a router or a firewall blocking UDP ports 67/68 can cause DHCP requests to never reach the server, resulting in APIPA addresses even when the DHCP server is healthy.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Network Troubleshooting — study guide chapter
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FAQ
Questions learners often ask
What does this N10-009 question test?
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 unavailable or the request is not reaching it — The IP address 169.254.25.100 with a subnet mask of 255.255.0.0 is an Automatic Private IP Addressing (APIPA) address, which is assigned by the operating system when a DHCP server is unavailable or the DHCP request fails. Since the user can connect to Wi-Fi but cannot access any network resources, the most likely cause is that the DHCP server is not responding or the DHCP discover/offer/request/ack sequence is failing, leaving the device with a link-local address that cannot route to the corporate network or internet.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on N10-009
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A user calls the help desk stating that they cannot access any network resources. The technician asks the user to run ipconfig and the output shows an IP address of 169.254.15.20 with a subnet mask of 255.255.0.0. Which of the following is the most likely cause?
easy- A.The DNS server is not responding
- ✓ B.The DHCP server is unreachable
- C.The default gateway is misconfigured
- D.There is a duplicate IP address on the network
Why B: The IP address 169.254.15.20 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 receive a lease from a DHCP server. Since the user cannot access any network resources, the most likely cause is that the DHCP server is unreachable, preventing the client from obtaining a valid IP address, default gateway, and DNS server settings.
Keep practising
More N10-009 practice questions
- Which layer of the OSI model is responsible for logical addressing and routing of packets between networks?
- Users in VLAN 10 cannot obtain IP addresses from a DHCP server located in VLAN 20. The router has an ip helper-address c…
- Which of the following is a characteristic of a Layer 2 network switch?
- Which of the following network devices operates primarily at Layer 2 of the OSI model and uses MAC addresses to forward…
- Which of the following is a characteristic of UDP when compared to TCP?
- Which of the following IPv6 addresses is a valid link-local address?
Last reviewed: Jun 11, 2026
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.
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