Question 959 of 2,015

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

Quick Answer

The answer is that the TACACS+ server upgrade changed the default authorization behavior from permissive to restrictive, requiring explicit permit statements for each command. This is correct because TACACS+ command authorization operates on a model where the router sends the full command string to the server, and the server’s rule set must explicitly match that string; after an upgrade, the server may enforce stricter parsing or require exact matching, causing previously allowed commands to be denied even though the router’s `aaa authorization commands 15 default group tacacs+` configuration remains unchanged. On the ENCOR 350-401 exam, this tests your understanding of AAA authorization models and the distinction between TACACS+ and RADIUS—specifically that TACACS+ separates authentication, authorization, and accounting, while RADIUS bundles them. A common trap is assuming the router configuration is at fault, but the logs showing requests and responses point to the server’s rule set. Remember: TACACS+ is “permit by default” only if configured that way; after an upgrade, check for “deny all” as the new implicit rule.

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

This 350-401 practice question tests your understanding of aaa, radius, and tacacs+. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.

An enterprise network uses TACACS+ for device administration and RADIUS for network access (VPN and wireless). The TACACS+ server is configured to authorize commands. A network engineer notices that after a recent upgrade of the TACACS+ server software, some commands that were previously authorized are now being denied. The engineer checks the router configuration and sees 'aaa authorization commands 15 default group tacacs+'. The TACACS+ server logs show that the authorization requests are being sent and responded to. 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 router's 'aaa authorization commands 15 default group tacacs+' command is missing the 'local' keyword, so if TACACS+ denies, there is no fallback.
Why wrong: Incorrect because the engineer wants TACACS+ to authorize commands, and the issue is that TACACS+ is responding with a deny, not that the router is failing to fall back. Adding 'local' would not help if TACACS+ explicitly denies.
B
The TACACS+ server upgrade changed the default authorization behavior from permissive to restrictive, requiring explicit 'permit' statements for each command, and the existing rules may not cover all commands.
Correct because TACACS+ authorization rules are defined on the server; an upgrade can change default behavior (e.g., from permit-all to deny-all), requiring updated rules to allow previously permitted commands.
C
The router's privilege level 15 is not correctly assigned to the user.
Why wrong: Incorrect because the user is already at privilege level 15 (as indicated by the 'commands 15' in the authorization command), and the issue is command authorization, not privilege level assignment.
D
The TACACS+ server is not reachable due to a firewall change, causing the router to deny all commands.
Why wrong: Incorrect because the scenario states that the TACACS+ server logs show authorization requests are being sent and responded to, indicating connectivity is fine.

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 upgrade changed the default authorization behavior from permissive to restrictive, requiring explicit 'permit' statements for each command, and the existing rules may not cover all commands.

The TACACS+ server software upgrade likely changed the authorization model or the way commands are matched. The router sends the full command string to the TACACS+ server, and the server must have a matching rule. If the server's configuration now requires exact matching or has stricter parsing, previously allowed commands may be denied.

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 router's 'aaa authorization commands 15 default group tacacs+' command is missing the 'local' keyword, so if TACACS+ denies, there is no fallback.
Why it's wrong here
Incorrect because the engineer wants TACACS+ to authorize commands, and the issue is that TACACS+ is responding with a deny, not that the router is failing to fall back. Adding 'local' would not help if TACACS+ explicitly denies.
✓
The TACACS+ server upgrade changed the default authorization behavior from permissive to restrictive, requiring explicit 'permit' statements for each command, and the existing rules may not cover all commands.
Why this is correct
Correct because TACACS+ authorization rules are defined on the server; an upgrade can change default behavior (e.g., from permit-all to deny-all), requiring updated rules to allow previously permitted commands.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
The router's privilege level 15 is not correctly assigned to the user.
Why it's wrong here
Incorrect because the user is already at privilege level 15 (as indicated by the 'commands 15' in the authorization command), and the issue is command authorization, not privilege level assignment.
✗
The TACACS+ server is not reachable due to a firewall change, causing the router to deny all commands.
Why it's wrong here
Incorrect because the scenario states that the TACACS+ server logs show authorization requests are being sent and responded to, indicating connectivity is fine.

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 engineer wants TACACS+ to authorize commands, and the issue is that TACACS+ is responding with a deny, not that the router is failing to fall back. Adding 'local' would not help if TACACS+ explicitly denies.
Scenario analysis trap
Incorrect because the scenario states that the TACACS+ server logs show authorization requests are being sent and responded to, indicating connectivity is fine.

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 upgrade changed the default authorization behavior from permissive to restrictive, requiring explicit 'permit' statements for each command, and the existing rules may not cover all commands. — The TACACS+ server software upgrade likely changed the authorization model or the way commands are matched. The router sends the full command string to the TACACS+ server, and the server must have a matching rule. If the server's configuration now requires exact matching or has stricter parsing, previously allowed commands may be denied.

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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