- A
The DHCP server is not authorized in Active Directory
Why wrong: DHCP server authorization is relevant for Windows environments but would not typically cause the client to receive an APIPA address; it would either fail or get a valid lease.
- B
The router does not have a DHCP relay (ip helper-address) configured
Without a DHCP relay, DHCP broadcast requests from the client in VLAN 10 cannot reach the DHCP server in VLAN 200, leading to APIPA assignment.
- C
The computer's NIC is faulty
Why wrong: A faulty NIC would likely show no link or erratic behavior, not a stable APIPA address. The client can obtain a link-local address, indicating the NIC is functional.
- D
The switch port is in the wrong VLAN
Why wrong: The technician already confirmed the port is in the correct VLAN. An incorrect VLAN would likely result in no network access at all, but the APIPA address suggests DHCP failure, not a VLAN mismatch.
Quick Answer
The answer is that the router lacks a DHCP relay (ip helper-address) configuration. When a DHCP client on VLAN 10 sends a broadcast request for an IP lease, that broadcast cannot cross the router into VLAN 200 where the DHCP server resides. Without a relay agent configured on the router’s interface facing VLAN 10, the broadcast is dropped, the server never receives the discover message, and the client falls back to Automatic Private IP Addressing (APIPA), resulting in the 169.254.x.x address seen in the ipconfig output. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of how DHCP operates across subnets and the critical role of a relay agent in forwarding broadcast traffic as unicast. A common trap is assuming the switch port or cabling is at fault, but the real issue is the missing relay. Remember: no relay, no lease—APIPA is the DHCP client’s last resort.
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 technician is troubleshooting a user's computer that cannot access any network resources. The technician runs ipconfig and sees an IP address of 169.254.18.33 with a subnet mask of 255.255.0.0. The computer is connected to a switch port configured for VLAN 10. The DHCP server is located in a different subnet (VLAN 200) and is reachable via a router. The technician confirms that the switch port is in the correct VLAN and that the cabling is good. Which of the following is the MOST likely cause of the issue?
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 router does not have a DHCP relay (ip helper-address) configured
The 169.254.x.x address is an Automatic Private IP Addressing (APIPA) address, assigned when a DHCP client fails to receive a lease. Since the DHCP server is on VLAN 200 and the client is on VLAN 10, a DHCP relay (ip helper-address) must be configured on the router interface facing VLAN 10 to forward DHCP broadcast requests as unicast to the DHCP server. Without this relay, the DHCP server never receives the client's discover message, causing the client to self-assign an APIPA address.
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 authorized in Active Directory
Why it's wrong here
DHCP server authorization is relevant for Windows environments but would not typically cause the client to receive an APIPA address; it would either fail or get a valid lease.
- ✓
The router does not have a DHCP relay (ip helper-address) configured
Why this is correct
Without a DHCP relay, DHCP broadcast requests from the client in VLAN 10 cannot reach the DHCP server in VLAN 200, leading to APIPA assignment.
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 computer's NIC is faulty
Why it's wrong here
A faulty NIC would likely show no link or erratic behavior, not a stable APIPA address. The client can obtain a link-local address, indicating the NIC is functional.
- ✗
The switch port is in the wrong VLAN
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates see a 169.254.x.x address and immediately blame a faulty NIC or DHCP server issue, overlooking the need for a DHCP relay when the server is on a different subnet.
Trap categories for this question
Command / output trap
A faulty NIC would likely show no link or erratic behavior, not a stable APIPA address. The client can obtain a link-local address, indicating the NIC is functional.
Detailed technical explanation
How to think about this question
DHCP relies on UDP broadcasts (ports 67/68), which are not forwarded across VLANs by default. The ip helper-address command on the router's VLAN 10 interface converts the broadcast into a unicast directed at the DHCP server, preserving the original client's giaddr (gateway IP address) so the server knows which subnet to lease from. In a real-world scenario, forgetting to configure ip helper-address on the correct interface is a common misconfiguration when deploying DHCP across routed networks.
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.
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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 router does not have a DHCP relay (ip helper-address) configured — The 169.254.x.x address is an Automatic Private IP Addressing (APIPA) address, assigned when a DHCP client fails to receive a lease. Since the DHCP server is on VLAN 200 and the client is on VLAN 10, a DHCP relay (ip helper-address) must be configured on the router interface facing VLAN 10 to forward DHCP broadcast requests as unicast to the DHCP server. Without this relay, the DHCP server never receives the client's discover message, causing the client to self-assign an APIPA address.
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
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