- A
The wireless clients do not support the correct EAP method.
Why wrong: If clients did not support the EAP method, the RADIUS server would still send a response indicating authentication failure. The log shows no response at all, indicating a connectivity issue.
- B
The firewall is blocking RADIUS traffic on UDP ports 1812 and 1813.
RADIUS uses specific UDP ports. If these are blocked, the RADIUS server cannot send back authentication responses, causing authentication to time out.
- C
The RADIUS server is not in the same broadcast domain as the wireless controller.
Why wrong: RADIUS is a Layer 7 protocol that operates over IP; it does not require the server to be in the same broadcast domain. Routers can forward the traffic.
- D
The SSID is not being broadcast.
Why wrong: If the SSID were not broadcast, clients would not see the network. However, they are attempting to authenticate, so visibility is not the issue.
Quick Answer
The answer is that the firewall is blocking RADIUS traffic on UDP ports 1812 and 1813. This is correct because the RADIUS server logs confirm authentication requests are received, but no responses are sent back, which points to return traffic being dropped by the firewall separating the wireless controller and server. RADIUS authentication uses UDP port 1812, and accounting uses UDP port 1813; both must be open in both directions for the server to reply to the controller. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of stateful firewall behavior and the common trap of only opening inbound ports while forgetting the return path. A key memory tip is to think of RADIUS as a two-way conversation: if the server hears the question but can’t answer, check that both UDP 1812 and 1813 are allowed through the firewall in both directions.
N10-009 Network Implementation Practice Question
This N10-009 practice question tests your understanding of network implementation. 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 company has deployed a WPA2-Enterprise wireless network. Users report that they cannot authenticate. The RADIUS server logs show that authentication attempts are received but no responses are sent back to the wireless controller. The wireless controller and RADIUS server are on different subnets, separated by a firewall. 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 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 firewall is blocking RADIUS traffic on UDP ports 1812 and 1813.
The RADIUS server logs show authentication attempts are received but no responses are sent back, indicating the request reached the server but the reply is being dropped. Since the wireless controller and RADIUS server are on different subnets separated by a firewall, the most likely cause is that the firewall is blocking the return RADIUS traffic. RADIUS uses UDP ports 1812 for authentication and 1813 for accounting, and these must be open in both directions for successful communication.
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 wireless clients do not support the correct EAP method.
Why it's wrong here
If clients did not support the EAP method, the RADIUS server would still send a response indicating authentication failure. The log shows no response at all, indicating a connectivity issue.
- ✓
The firewall is blocking RADIUS traffic on UDP ports 1812 and 1813.
Why this is correct
RADIUS uses specific UDP ports. If these are blocked, the RADIUS server cannot send back authentication responses, causing authentication to time out.
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 RADIUS server is not in the same broadcast domain as the wireless controller.
Why it's wrong here
RADIUS is a Layer 7 protocol that operates over IP; it does not require the server to be in the same broadcast domain. Routers can forward the traffic.
- ✗
The SSID is not being broadcast.
Why it's wrong here
If the SSID were not broadcast, clients would not see the network. However, they are attempting to authenticate, so visibility is not the issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the issue is with client configuration (EAP method) or layer 2 connectivity (broadcast domain), when the symptom of 'requests received but no responses sent' points directly to a firewall blocking the return path, a classic network-layer troubleshooting scenario.
Trap categories for this question
Command / output trap
If clients did not support the EAP method, the RADIUS server would still send a response indicating authentication failure. The log shows no response at all, indicating a connectivity issue.
Detailed technical explanation
How to think about this question
RADIUS uses UDP, which is connectionless and does not retransmit lost packets; if the firewall drops the response packet, the wireless controller will timeout and the authentication fails silently. The RADIUS server may log the request as received but never see a retransmission because the controller's timeout is typically 5-10 seconds. In real-world deployments, administrators often forget to open the ephemeral source ports (typically above 1023) for the return traffic, or misconfigure stateful firewall rules that only allow inbound RADIUS traffic.
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
What to study next
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FAQ
Questions learners often ask
What does this N10-009 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The firewall is blocking RADIUS traffic on UDP ports 1812 and 1813. — The RADIUS server logs show authentication attempts are received but no responses are sent back, indicating the request reached the server but the reply is being dropped. Since the wireless controller and RADIUS server are on different subnets separated by a firewall, the most likely cause is that the firewall is blocking the return RADIUS traffic. RADIUS uses UDP ports 1812 for authentication and 1813 for accounting, and these must be open in both directions for successful communication.
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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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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