The answer is that the DHCP server is unavailable or unreachable. This is correct because the IP address 169.254.100.25 with a 255.255.0.0 subnet mask is an Automatic Private IP Addressing (APIPA) address, which Windows assigns automatically when a DHCP client fails to obtain a lease from a DHCP server. The blank Default Gateway confirms that no DHCP server responded, so the workstation is limited to local subnet communication only, explaining the inability to access company resources. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of DHCP failure and APIPA as a fallback mechanism; a common trap is assuming the issue is a misconfigured static IP or a faulty NIC, but the 169.254.x.x range specifically points to a DHCP server problem. Remember the memory tip: “169.254 means DHCP is no more”—if 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 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?
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.
Why wrong: DNS failure would cause name resolution issues, but the workstation would still get a proper DHCP IP. APIPA addresses appear only when DHCP fails.
B
The DHCP server is unavailable or unreachable.
APIPA is assigned when a DHCP client cannot contact a DHCP server; this is the most likely cause.
C
The workstation has a static IP address configured.
Why wrong: A static IP would not result in 169.254.x.x; APIPA is only used when DHCP fails and no static IP is set.
D
The network cable is unplugged.
Why wrong: If the cable were unplugged, the NIC would not have a link and likely show a disconnected status, not an APIPA address. APIPA requires a link to be active.
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.
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
DNS failure would cause name resolution issues, but the workstation would still get a proper DHCP IP. APIPA addresses appear only when DHCP fails.
✓
The DHCP server is unavailable or unreachable.
Why this is correct
APIPA is assigned when a DHCP client cannot contact a DHCP server; this is the most likely cause.
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 workstation has a static IP address configured.
Why it's wrong here
A static IP would not result in 169.254.x.x; APIPA is only used when DHCP fails and no static IP is set.
✗
The network cable is unplugged.
Why it's wrong here
If the cable were unplugged, the NIC would not have a link and likely show a disconnected status, not an APIPA address. APIPA requires a link to be active.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often 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.
Trap categories for this question
Command / output trap
If the cable were unplugged, the NIC would not have a link and likely show a disconnected status, not an APIPA address. APIPA requires a link to be active.
Detailed technical explanation
How to think about this question
APIPA is defined in RFC 3927 and uses the 169.254.0.0/16 range, with the client performing a gratuitous ARP probe to ensure no duplicate IP exists before assigning itself an address. In a corporate environment, this often indicates a VLAN mismatch, a DHCP relay misconfiguration, or a switchport issue that prevents DHCP discovery broadcasts (UDP port 67/68) from reaching the 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 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.
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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