The answer is that the VTY lines are missing the login authentication default command. This is the most likely cause because the global AAA authentication login default group radius local command only defines the authentication method list; it does not automatically apply it to the VTY lines. Without explicitly binding that default list to the VTY lines using login authentication default, the router falls back to its default behavior of using the local enable password for Telnet or SSH authentication, ignoring the RADIUS server entirely. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that AAA configuration is a two-step process—defining the method list globally and then applying it to the specific lines. A common trap is assuming the global default command alone secures remote access, but the VTY lines must be explicitly told to use it. Memory tip: think of it as “global defines, VTY applies”—without the line-level command, AAA is just a ghost policy.
300-410 Device Access Control Practice Question
This 300-410 practice question tests your understanding of device access control. 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.
A network administrator is configuring AAA for device access on a Cisco router. After configuring the RADIUS server and AAA authentication login default group radius local, the engineer tests Telnet access and receives 'Access denied' even with correct credentials. The RADIUS server is reachable. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VTY lines are not configured with 'login authentication default'.
The 'login authentication default' command must be applied to the VTY lines to use the AAA authentication method set globally with 'aaa authentication login default group radius local'. Without this, the VTY lines default to using the local enable password for authentication, ignoring the AAA configuration. Since the RADIUS server is reachable and credentials are correct, the missing VTY line configuration is the most likely cause of the 'Access denied' error.
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 VTY lines are not configured with 'login authentication default'.
Why this is correct
Correct because the AAA login method list must be explicitly applied to the VTY lines using the 'login authentication' command.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The RADIUS server shared key is incorrect.
Why it's wrong here
Incorrect because the RADIUS server is reachable, and the issue is specific to AAA application on VTY lines.
✗
The enable password is not set.
Why it's wrong here
Incorrect because AAA login authentication does not require an enable password; the issue is with the method list application.
✗
The 'aaa new-model' command is missing.
Why it's wrong here
Incorrect because if 'aaa new-model' were missing, the AAA commands would not be accepted; the configuration exists but is not applied.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between global AAA authentication configuration and per-line application, trapping candidates who assume 'aaa authentication login default' automatically applies to all lines without the 'login authentication default' command on the VTY lines.
Trap categories for this question
Command / output trap
Incorrect because if 'aaa new-model' were missing, the AAA commands would not be accepted; the configuration exists but is not applied.
Detailed technical explanation
How to think about this question
When 'aaa new-model' is enabled, all login methods (including VTY) default to using the local database unless explicitly overridden. The 'login authentication default' command on VTY lines ties the line to the AAA authentication list; if omitted, the line uses its own default method (typically 'password' or 'enable'). In real-world deployments, forgetting to apply the authentication method to the VTY lines is a common misconfiguration that leads to access failures despite correct AAA server settings.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Device Access Control — This question tests Device Access Control — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The VTY lines are not configured with 'login authentication default'. — The 'login authentication default' command must be applied to the VTY lines to use the AAA authentication method set globally with 'aaa authentication login default group radius local'. Without this, the VTY lines default to using the local enable password for authentication, ignoring the AAA configuration. Since the RADIUS server is reachable and credentials are correct, the missing VTY line configuration is the most likely cause of the 'Access denied' error.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
About these practice questions
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Variation 1. Which TWO statements about AAA authentication on Cisco IOS-XE are true? (Choose TWO.)
hard
A.If no AAA authentication method list is explicitly configured, the default method list uses the local user database.
✓ B.The 'aaa authentication login default local' command creates a default method list that uses the local user database for login authentication.
✓ C.When a named method list is applied to a line with 'login authentication LISTNAME', the default method list is ignored for that line.
D.The 'aaa authentication login default group radius local' command will first try RADIUS, and if RADIUS fails (not just rejects), it will fall back to local.
E.The 'aaa authentication login default method' command creates a method list with no authentication methods, which denies all login attempts.
Why B: Option B is correct because the 'aaa authentication login default local' command explicitly configures the default method list to use the local user database for login authentication. This is the standard way to define a fallback or primary local authentication method for all lines that do not have a named method list applied.
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Question Discussion
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