350-401 Infrastructure Practice Question
A network administrator is configuring a Cisco IOS router to authenticate management users against a TACACS+ server. The administrator wants to ensure that if the TACACS+ server becomes unreachable, a local username and password can still be used to log in. Which configuration accomplishes this requirement?
⚠ Common exam trap
Watch out — candidates often confuse the order of authentication methods; the first method is primary, and subsequent methods are fallbacks. Placing 'local' first would make it primary, which is not desired.
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 method list must list 'group tacacs+' before 'local' so that TACACS+ is tried first, and local is used only if the server is unreachable. The 'local' keyword ensures that the local username database is used as a fallback. Other keywords like 'enable' or 'none' do not provide the required local username and password fallback.
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 local group tacacs+
Why it's wrong here
This configuration attempts local authentication first, and only if that fails does it try TACACS+. This reverses the desired order; the administrator wants TACACS+ to be primary and local as backup. With this order, local accounts are checked first, which is not the intended behavior.
- ✓
aaa authentication login default group tacacs+ local
Why this is correct
This command configures AAA authentication for login using TACACS+ first, then falls back to the local database if the TACACS+ server is unreachable. The 'local' keyword ensures that local authentication is attempted only if the TACACS+ servers do not respond, providing a failover mechanism for management access.
- ✗
aaa authentication login default group tacacs+ none
Why it's wrong here
The 'none' keyword means no authentication is required if TACACS+ is unavailable, which is insecure and does not use a local username and password. This would allow access without any credentials, violating the requirement for fallback to local authentication.
- ✗
aaa authentication login default group tacacs+ enable
Why it's wrong here
The 'enable' keyword uses the enable password as a fallback, not a local username and password. While it provides a fallback method, it does not meet the requirement of using a local username and password. The enable password is a shared secret and less granular than individual local accounts.
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.