The correct answer is that the local username database is used when the TACACS+ server is unreachable. This occurs because the command `aaa authentication login default group tacacs+ local` creates a method list where TACACS+ is tried first, and if it is unreachable—meaning it does not respond or times out—the system automatically falls back to the next method, which is local authentication. On the Cisco DCCOR 350-601 exam, this tests your understanding of AAA method list fallback behavior, a common topic where the trap is confusing a server rejection (which stops the process) with a server being unreachable (which triggers the fallback). Remember the key distinction: "unreachable" means no response, so the router moves to the backup; "rejected" means the server said no, so authentication fails outright. A useful memory tip is "TACACS+ timeout? Try local."
350-601 Security Practice Question
This 350-601 practice question tests your understanding of security. 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.
An administrator configures 'aaa authentication login default group tacacs+ local'. What happens if the TACACS+ server is unreachable?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Local username database is used
The command 'aaa authentication login default group tacacs+ local' configures a method list where the first method is TACACS+ and the second is local. If the TACACS+ server is unreachable (not responding, not rejecting), the switch falls back to the next method in the list, which is local authentication using the local username database. This fallback behavior is defined by Cisco IOS/IOS-XE authentication method lists, where 'local' acts as a backup when the primary method is unavailable.
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 switch uses no authentication
Why it's wrong here
Authentication always uses a method; local is used if TACACS+ is unreachable.
✗
Authentication fails
Why it's wrong here
The fallback to local prevents immediate failure.
✗
The switch tries the next method in the group
Why it's wrong here
The group is tried first; if it fails, only then local is used, not within the same group.
✓
Local username database is used
Why this is correct
The config includes 'local' as a fallback method after group tacacs+.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between a server being unreachable (fallback occurs) versus a server rejecting credentials (authentication fails immediately), causing candidates to incorrectly assume that any TACACS+ issue results in authentication failure.
Detailed technical explanation
How to think about this question
Under the hood, Cisco IOS treats TACACS+ server unreachability (e.g., timeout or no response) as a 'method failure' that triggers fallback to the next method in the list, whereas a server response of 'REJECT' (authentication denied) is a 'method success' that stops the list and fails authentication. This distinction is critical: 'unreachable' vs. 'rejected' determines whether fallback occurs, and the 'group tacacs+' keyword defines a server group, not a list of methods—so only one method (TACACS+) is tried before moving to 'local'.
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Local username database is used — The command 'aaa authentication login default group tacacs+ local' configures a method list where the first method is TACACS+ and the second is local. If the TACACS+ server is unreachable (not responding, not rejecting), the switch falls back to the next method in the list, which is local authentication using the local username database. This fallback behavior is defined by Cisco IOS/IOS-XE authentication method lists, where 'local' acts as a backup when the primary method is unavailable.
What should I do if I get this 350-601 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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