- A
The DHCP server is not reachable from the router
Why wrong: The scenario states that users can ping the DHCP server from the router, so the server is reachable.
- B
The DHCP server scope does not include the VLAN 10 subnet
Even if the DHCP server receives the request, it will not offer an IP address if it has no scope configured for the subnet of the requesting client (VLAN 10).
- C
The router's ip helper-address is configured incorrectly
Why wrong: Ping success indicates the router can reach the server, so the helper address is likely correct. The issue is on the server side.
- D
The switch ports are not configured for VLAN 10
Why wrong: If ports were in the wrong VLAN, clients would likely not even obtain APIPA addresses or communicate with the router at all.
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.
Users in VLAN 10 cannot obtain IP addresses from a DHCP server located in VLAN 20. The router has an ip helper-address configured on VLAN 10 interface pointing to the DHCP server. Users can ping the DHCP server IP from the router. However, users are receiving APIPA addresses. 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 scope does not include the VLAN 10 subnet
The correct answer is B because the DHCP server must have a scope configured for the subnet of the requesting clients (VLAN 10) to assign IP addresses from that range. Since users receive APIPA addresses (169.254.x.x), the DHCP discovery process is failing, which typically occurs when the server receives the request via the ip helper-address but has no matching scope for VLAN 10. The router's ability to ping the server confirms Layer 3 reachability, isolating the issue to the server's scope configuration.
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 DHCP server is not reachable from the router
Why it's wrong here
The scenario states that users can ping the DHCP server from the router, so the server is reachable.
- ✓
The DHCP server scope does not include the VLAN 10 subnet
Why this is correct
Even if the DHCP server receives the request, it will not offer an IP address if it has no scope configured for the subnet of the requesting client (VLAN 10).
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 router's ip helper-address is configured incorrectly
Why it's wrong here
Ping success indicates the router can reach the server, so the helper address is likely correct. The issue is on the server side.
- ✗
The switch ports are not configured for VLAN 10
Why it's wrong here
If ports were in the wrong VLAN, clients would likely not even obtain APIPA addresses or communicate with the router at all.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a successful ping from the router to the DHCP server guarantees DHCP functionality, but the trap here is that the ip helper-address only relays the request; the server must still have a scope for the client's subnet to assign an address.
Trap categories for this question
Scenario analysis trap
The scenario states that users can ping the DHCP server from the router, so the server is reachable.
Detailed technical explanation
How to think about this question
The ip helper-address command uses DHCP relay (RFC 2131) to convert a broadcast DHCPDISCOVER into a unicast destined for the server, but the server's response (DHCPOFFER) must include a valid IP from a scope that matches the client's subnet (the giaddr field in the DHCP packet). If no scope exists for VLAN 10, the server either drops the request or offers an address from a different scope, causing the client to reject it and fall back to APIPA. In real-world scenarios, this often occurs when network administrators add new VLANs but forget to create corresponding scopes on 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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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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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 scope does not include the VLAN 10 subnet — The correct answer is B because the DHCP server must have a scope configured for the subnet of the requesting clients (VLAN 10) to assign IP addresses from that range. Since users receive APIPA addresses (169.254.x.x), the DHCP discovery process is failing, which typically occurs when the server receives the request via the ip helper-address but has no matching scope for VLAN 10. The router's ability to ping the server confirms Layer 3 reachability, isolating the issue to the server's scope configuration.
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
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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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