Question 1,669 of 2,015

AAA, RADIUS, and TACACS+ →hardMultiple ChoiceObjective-mapped

350-401 AAA, RADIUS, and TACACS+ Practice Question

This 350-401 practice question tests your understanding of aaa, radius, and tacacs+. 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 is deploying a new Cisco wireless LAN controller (WLC) and wants to use RADIUS for authenticating wireless users. The WLC is configured with the RADIUS server IP, shared secret, and authentication port 1812. However, users are unable to authenticate. The network engineer checks the RADIUS server logs and sees that the server is receiving authentication requests from the WLC but is responding with an 'Access-Reject' message. The WLC logs show 'RADIUS server not responding' for the same server. 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.

Question 1hardmultiple choice

Read the full wireless explanation →

A
The RADIUS server is configured to use a different source IP address for RADIUS responses than the IP address configured on the WLC, causing the WLC to drop the responses.
Correct because the WLC typically expects RADIUS responses to come from the same IP address as the configured server; if the server uses a different source IP (e.g., a loopback or secondary IP), the WLC may not recognize the response and logs 'server not responding'.
B
The WLC is configured with the wrong authentication port; RADIUS uses port 1645, not 1812.
Why wrong: Incorrect because RADIUS officially uses UDP port 1812 for authentication; port 1645 is legacy and rarely used. The scenario uses 1812, which is correct.
C
The WLC's RADIUS server configuration has the wrong shared secret, causing the server to reject requests.
Why wrong: Incorrect because the server logs show 'Access-Reject', which indicates the server received the request and processed it; a shared secret mismatch would typically result in no response or a 'Access-Challenge' but not necessarily a reject. However, the server could still reject if the secret is wrong, but the WLC would still see a response, not 'server not responding'.
D
The WLC is not configured with a valid management interface IP address to reach the RADIUS server.
Why wrong: Incorrect because the server logs show that requests are being received, so the WLC can reach the server; the issue is with the response.

Full breakdown with real-world context →

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 RADIUS server is configured to use a different source IP address for RADIUS responses than the IP address configured on the WLC, causing the WLC to drop the responses.

The WLC is interpreting the 'Access-Reject' as a non-response because the RADIUS server is using a different source port for the response, or the WLC is not configured to accept responses from the server's source IP. However, the most common cause is that the RADIUS server is sending the response from a different IP address than the one configured on the WLC, or the WLC has a mismatch in the shared secret. But since the server logs show requests are received and rejected, the shared secret is likely correct. The issue is that the WLC might be expecting the response on a different port or from a different IP, but the scenario says 'RADIUS server not responding' which typically means the WLC did not receive a response. This could be due to the RADIUS server sending the response from a different source IP (e.g., a secondary IP) than the one configured on the WLC, or a firewall blocking the response. However, the most plausible cause is that the RADIUS server is configured to use a different source IP for RADIUS traffic than the one the WLC expects.

Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.

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 RADIUS server is configured to use a different source IP address for RADIUS responses than the IP address configured on the WLC, causing the WLC to drop the responses.
Why this is correct
Correct because the WLC typically expects RADIUS responses to come from the same IP address as the configured server; if the server uses a different source IP (e.g., a loopback or secondary IP), the WLC may not recognize the response and logs 'server not responding'.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
The WLC is configured with the wrong authentication port; RADIUS uses port 1645, not 1812.
Why it's wrong here
Incorrect because RADIUS officially uses UDP port 1812 for authentication; port 1645 is legacy and rarely used. The scenario uses 1812, which is correct.
✗
The WLC's RADIUS server configuration has the wrong shared secret, causing the server to reject requests.
Why it's wrong here
Incorrect because the server logs show 'Access-Reject', which indicates the server received the request and processed it; a shared secret mismatch would typically result in no response or a 'Access-Challenge' but not necessarily a reject. However, the server could still reject if the secret is wrong, but the WLC would still see a response, not 'server not responding'.
✗
The WLC is not configured with a valid management interface IP address to reach the RADIUS server.
Why it's wrong here
Incorrect because the server logs show that requests are being received, so the WLC can reach the server; the issue is with the response.

Common exam traps

Common exam trap: authentication is not authorization

Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.

Trap categories for this question

Command / output trap
Incorrect because the server logs show 'Access-Reject', which indicates the server received the request and processed it; a shared secret mismatch would typically result in no response or a 'Access-Challenge' but not necessarily a reject. However, the server could still reject if the secret is wrong, but the WLC would still see a response, not 'server not responding'.
Scenario analysis trap
Incorrect because RADIUS officially uses UDP port 1812 for authentication; port 1645 is legacy and rarely used. The scenario uses 1812, which is correct.

Detailed technical explanation

How to think about this question

This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.

KKey Concepts to Remember

Authentication checks who the user is.
Authorization controls what the user is allowed to do after login.
Privilege levels affect access to EXEC and configuration commands.
AAA, TACACS+ and RADIUS can separate login success from command access.

TExam Day Tips

Do not assume successful login means full administrative access.
Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
Separate login problems from permission problems before choosing the answer.

Key takeaway

Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.

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

Got this wrong? Here's your next step.

Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related 350-401 questions on access control and AAA configuration.

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FAQ

Questions learners often ask

What does this 350-401 question test?

AAA, RADIUS, and TACACS+ — This question tests AAA, RADIUS, and TACACS+ — Authentication checks who the user is..

What is the correct answer to this question?

The correct answer is: The RADIUS server is configured to use a different source IP address for RADIUS responses than the IP address configured on the WLC, causing the WLC to drop the responses. — The WLC is interpreting the 'Access-Reject' as a non-response because the RADIUS server is using a different source port for the response, or the WLC is not configured to accept responses from the server's source IP. However, the most common cause is that the RADIUS server is sending the response from a different IP address than the one configured on the WLC, or the WLC has a mismatch in the shared secret. But since the server logs show requests are received and rejected, the shared secret is likely correct. The issue is that the WLC might be expecting the response on a different port or from a different IP, but the scenario says 'RADIUS server not responding' which typically means the WLC did not receive a response. This could be due to the RADIUS server sending the response from a different source IP (e.g., a secondary IP) than the one configured on the WLC, or a firewall blocking the response. However, the most plausible cause is that the RADIUS server is configured to use a different source IP for RADIUS traffic than the one the WLC expects.

What should I do if I get this 350-401 question wrong?

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?

Authentication checks who the user is.

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