Question 1,476 of 2,015

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

Quick Answer

The answer is that the TACACS+ server is not configured to authorize the user for EXEC access, sending a deny response that causes the router to disconnect. This occurs because the `aaa authorization exec default group tacacs+ local` command instructs the router to first query TACACS+ for EXEC authorization; while authentication succeeded, a deny from TACACS+ for the shell profile overrides the local fallback and terminates the session immediately. On the ENCOR 350-401 exam, this scenario tests your understanding of the AAA authorization flow—specifically that a deny response from TACACS+ is final, unlike a non-response which triggers the local method. A common trap is assuming the local fallback will save the user if TACACS+ responds at all, but any explicit deny from the server blocks access. Memory tip: “AuthN opens the door, AuthZ decides if you can sit down—if TACACS+ says no chair, you’re out.”

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 network engineer is configuring a Cisco router to use TACACS+ for authentication and authorization of EXEC sessions. The engineer configures 'aaa new-model', 'aaa authentication login default group tacacs+ local', and 'aaa authorization exec default group tacacs+ local'. When a user tries to log in via SSH, the router prompts for username and password, but after entering correct credentials, the user is immediately disconnected. The TACACS+ server logs show that the authentication was successful. 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.
Clue: "immediately / without restart"
Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.

Question 1hardmultiple choice

Study the full AAA explanation →

A
The TACACS+ server is not configured to authorize the user for EXEC access, so it sends a 'deny' response, causing the router to disconnect the user.
Correct because TACACS+ authorization for EXEC determines whether the user is allowed to start a shell; if the server denies, the router disconnects even though authentication succeeded.
B
The 'aaa authorization exec' command should be 'aaa authorization commands 15' to allow the user to execute commands after login.
Why wrong: Incorrect because 'aaa authorization exec' controls whether the user gets a shell at all; command authorization is separate and would not cause immediate disconnection.
C
The router's SSH configuration is missing the 'ip ssh authentication-retries' command.
Why wrong: Incorrect because the user is able to authenticate but is disconnected after; this is not related to SSH retries.
D
The 'local' fallback in the authorization command is overriding the TACACS+ response.
Why wrong: Incorrect because the fallback only occurs if TACACS+ does not respond; if TACACS+ responds with a deny, the fallback is not used.

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 TACACS+ server is not configured to authorize the user for EXEC access, so it sends a 'deny' response, causing the router to disconnect the user.

The user is authenticated successfully, but the authorization for EXEC (shell) is failing. The 'aaa authorization exec default group tacacs+ local' command means the router will first try TACACS+ for EXEC authorization; if TACACS+ does not respond, it falls back to local. However, if TACACS+ responds with a deny for EXEC authorization, the user is denied access and disconnected. The TACACS+ server may not have a shell profile for the user, or the authorization rule denies EXEC access.

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 TACACS+ server is not configured to authorize the user for EXEC access, so it sends a 'deny' response, causing the router to disconnect the user.
Why this is correct
Correct because TACACS+ authorization for EXEC determines whether the user is allowed to start a shell; if the server denies, the router disconnects even though authentication succeeded.
Clue confirmation
The clue words "most likely", "immediately / without restart" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
The 'aaa authorization exec' command should be 'aaa authorization commands 15' to allow the user to execute commands after login.
Why it's wrong here
Incorrect because 'aaa authorization exec' controls whether the user gets a shell at all; command authorization is separate and would not cause immediate disconnection.
✗
The router's SSH configuration is missing the 'ip ssh authentication-retries' command.
Why it's wrong here
Incorrect because the user is able to authenticate but is disconnected after; this is not related to SSH retries.
✗
The 'local' fallback in the authorization command is overriding the TACACS+ response.
Why it's wrong here
Incorrect because the fallback only occurs if TACACS+ does not respond; if TACACS+ responds with a deny, the fallback is not used.

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 'aaa authorization exec' controls whether the user gets a shell at all; command authorization is separate and would not cause immediate disconnection.

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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

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 TACACS+ server is not configured to authorize the user for EXEC access, so it sends a 'deny' response, causing the router to disconnect the user. — The user is authenticated successfully, but the authorization for EXEC (shell) is failing. The 'aaa authorization exec default group tacacs+ local' command means the router will first try TACACS+ for EXEC authorization; if TACACS+ does not respond, it falls back to local. However, if TACACS+ responds with a deny for EXEC authorization, the user is denied access and disconnected. The TACACS+ server may not have a shell profile for the user, or the authorization rule denies EXEC access.

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", "immediately / without restart". 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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