The answer is that the `aaa authentication login default` command must include `group tacacs+` before `local`. This is because the authentication method list defines the order in which the router consults authentication servers; by placing `group tacacs+` first, the router will attempt TACACS+ authentication before falling back to the local database, ensuring VTY users are authenticated via the external server. On the ENCOR 350-401 exam, this scenario tests your understanding of AAA method list priority and the common trap of assuming that enabling `aaa new-model` alone or configuring accounting for TACACS+ is sufficient for authentication. The exam often presents a configuration where accounting or authorization points to TACACS+, but the authentication method list still defaults to local, making it a frequent trick question. Remember the mnemonic “AAA: Authenticate first, then Authorize, then Account”—if the authentication list doesn’t include the TACACS+ group, the server is never consulted for login.
350-401 AAA, RADIUS, and TACACS+ Practice Question
This 350-401 practice question tests your understanding of aaa, radius, and tacacs+. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Examine this configuration:
aaa new-model
aaa authentication login default local
aaa authorization exec default local
aaa accounting exec default start-stop group tacacs+
line vty 0 4
login authentication default
privilege level 15
What is missing to ensure that VTY users are authenticated via TACACS+?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'aaa authentication login default' command should include 'group tacacs+' before 'local'.
The authentication method list 'default' uses local authentication. To use TACACS+, the method list must include 'group tacacs+' before 'local'. The current configuration only uses local.
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 'aaa authentication login default' command should include 'group tacacs+' before 'local'.
Why this is correct
Correct. To authenticate via TACACS+, the method list must specify 'group tacacs+' as the primary method.
Related concept
Authentication checks who the user is.
✗
The 'aaa authorization exec default' command should include 'group tacacs+'.
Why it's wrong here
Incorrect. Authorization is separate from authentication; the question asks about authentication.
✗
The 'aaa accounting exec default' command should include 'group tacacs+'.
Why it's wrong here
Incorrect. Accounting does not affect authentication.
✗
The 'privilege level 15' command under VTY lines is missing.
Why it's wrong here
Incorrect. Privilege level is already configured; it does not affect authentication method.
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.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
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.
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 'aaa authentication login default' command should include 'group tacacs+' before 'local'. — The authentication method list 'default' uses local authentication. To use TACACS+, the method list must include 'group tacacs+' before 'local'. The current configuration only uses local.
What should I do if I get this 350-401 question wrong?
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.
What is the key concept behind this question?
Authentication checks who the user is.
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