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Quick Answer
The correct answer includes configuring TACACS+ for detailed command authorization and accounting, using a local username database as a fallback method, and enabling aaa new-model. TACACS+ is preferred over RADIUS for Cisco routers because it encrypts the entire packet and supports per-command authorization and accounting, whereas RADIUS only encrypts the password. The local fallback ensures administrative access remains possible if the AAA server becomes unreachable, preventing accidental lockout—a critical AAA best practice for TACACS+ local fallback scenarios. On the CCNA 200-301 v2 exam, this concept tests your understanding of AAA protocol differences and redundancy planning; a common trap is selecting RADIUS for command authorization, which it cannot perform. Remember the mnemonic “TACACS+ Talks Commands, RADIUS Only Passwords” to distinguish their roles.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and 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.
Which three of the following are security best practices for implementing AAA on a Cisco router? (Choose three.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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
✓
Use a local username database as a fallback method if the AAA server is unreachable.
Using a local username database as a fallback method ensures that if the AAA server becomes unreachable, administrators can still authenticate via the router's local accounts. This is a standard best practice to prevent lockout. Enabling 'aaa new-model' is mandatory before any AAA configuration, as it activates the AAA subsystem on the router. TACACS+ is the preferred protocol for command authorization and accounting because it encrypts the entire packet and supports per-command authorization, unlike RADIUS which only encrypts the password.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that RADIUS can be used for command authorization, but the trap is that RADIUS only supports authentication and accounting for network access, not the granular command-level control that TACACS+ provides.
Detailed technical explanation
How to think about this question
Under the hood, 'aaa new-model' modifies the router's authentication process by replacing the legacy enable and line password checks with a modular AAA framework that can reference local, RADIUS, or TACACS+ servers. TACACS+ uses TCP port 49 and separates authentication, authorization, and accounting into distinct processes, allowing an administrator to authorize specific commands (e.g., 'configure terminal') while denying others. In a real-world scenario, an enterprise might configure TACACS+ for all SSH and console access but keep a local username/password as a backup to avoid being locked out during a WAN outage.
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
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Services and Security — This question tests Network Services and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a local username database as a fallback method if the AAA server is unreachable. — Using a local username database as a fallback method ensures that if the AAA server becomes unreachable, administrators can still authenticate via the router's local accounts. This is a standard best practice to prevent lockout. Enabling 'aaa new-model' is mandatory before any AAA configuration, as it activates the AAA subsystem on the router. TACACS+ is the preferred protocol for command authorization and accounting because it encrypts the entire packet and supports per-command authorization, unlike RADIUS which only encrypts the password.
What should I do if I get this 200-301 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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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