350-401 Infrastructure Practice Question
A network administrator is configuring a Cisco IOS router to authenticate management users via TACACS+. The requirement is to allow fallback to the local database if all TACACS+ servers are unreachable. Which AAA configuration achieves this?
⚠ Common exam trap
Many candidates confuse the order of authentication methods or using 'none' or 'enable' instead of 'local' for fallback, which either compromises security or fails to use the local database.
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
✓
aaa authentication login default group tacacs+ local
The correct configuration uses the default method list with TACACS+ first and local fallback. The 'group tacacs+' keyword specifies TACACS+ servers, and 'local' ensures the router's local username database is used if all TACACS+ servers are unreachable. This provides centralized authentication with a resilient backup.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
aaa authentication login default group tacacs+ none
Why it's wrong here
The 'none' keyword allows authentication to succeed without any credentials if TACACS+ fails, which is a severe security risk. It does not use the local database, so it fails the requirement for fallback to local authentication. This configuration would permit unauthenticated access, which is unacceptable.
- ✗
aaa authentication login default local group tacacs+
Why it's wrong here
This method list attempts local authentication first and only then TACACS+. That reverses the intended order: the requirement is to use TACACS+ primarily and fall back to local only if TACACS+ is unreachable. Local-first would bypass centralized authentication for all users, defeating the purpose of TACACS+.
- ✗
aaa authentication login default group tacacs+ enable
Why it's wrong here
The 'enable' keyword uses the enable password as a fallback, not the local username database. This does not meet the requirement of local database fallback and may not provide per-user authentication. It also relies on a shared enable secret, which is less secure and not user-specific.
- ✓
aaa authentication login default group tacacs+ local
Why this is correct
This command configures the default login authentication method list to try TACACS+ first, then fall back to the local username database if the TACACS+ servers do not respond. The 'local' keyword ensures that local authentication is used as a backup, providing administrative access even when the AAA server is unreachable.
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 350-401 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 350-401 exam.