300-410 Infrastructure Security Practice Question
A network administrator is configuring AAA on a Cisco IOS router. The administrator wants to authenticate administrative users against a TACACS+ server and ensure that if the TACACS+ server is unreachable, the router falls back to local authentication. The administrator has configured the TACACS+ server and local user accounts. Which additional configuration is required to achieve this?
⚠ Common exam trap
It's easy for candidates to confuse the order of authentication methods or using 'enable' as a fallback instead of 'local', which does not provide local user authentication.
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
✓
Configure 'aaa authentication login default group tacacs+ local'.
The correct command is 'aaa authentication login default group tacacs+ local', which specifies TACACS+ as the primary authentication method and local as the fallback. This ensures that if the TACACS+ server is unreachable, the router will use the local user database. Other options either reverse the order or use different methods that do not meet the fallback requirement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure 'aaa authentication login default local group tacacs+'.
Why it's wrong here
This command reverses the order, attempting local authentication first and then TACACS+. This would not use TACACS+ as the primary method when it is available, contrary to the requirement. The administrator wants TACACS+ first, so this order is incorrect.
- ✓
Configure 'aaa authentication login default group tacacs+ local'.
Why this is correct
The 'aaa authentication login default group tacacs+ local' command configures the router to first attempt authentication via TACACS+ and then fall back to the local database if the TACACS+ server is unreachable. This meets the requirement for fallback authentication.
- ✗
Configure 'aaa authentication login default group tacacs+ enable'.
Why it's wrong here
Using 'enable' as a fallback method requires the enable password, not local user accounts. This does not meet the requirement to use local authentication. The 'enable' method is typically used for privileged EXEC access, not for general login authentication.
- ✗
Configure 'aaa authorization exec default group tacacs+ local'.
Why it's wrong here
This command configures authorization for EXEC sessions, not authentication. The requirement is for authentication fallback. Authorization controls what commands or services a user can access after authentication, so this does not address the authentication fallback need.
Quick reference
AAA Protocol Comparison
| Protocol | Port(s) | Encryption | Transport | Primary Use |
|---|---|---|---|---|
| RADIUS | 1812 / 1813 | Password only | UDP | Network access control |
| TACACS+ | 49 | Full packet | TCP | Device administration |
| Diameter | 3868 | Full session | TCP / SCTP | Carrier / mobile networks |
| 802.1X | — | EAP-based | Layer 2 | Port-based access control |
TACACS+ encrypts the entire packet; RADIUS only encrypts the password field — a key exam distinction.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.