350-401 Infrastructure Practice Question
A network engineer is configuring a Cisco IOS router to authenticate management users against a RADIUS server. The engineer wants to ensure that if the RADIUS server is unreachable, the router falls back to local authentication using the local username database. Which configuration should be applied?
⚠ Common exam trap
The trap here is reversing the order of methods or using 'enable' or 'none' as fallback, which do not provide local database fallback.
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 radius local
The correct configuration uses 'group radius' followed by 'local' to ensure that RADIUS is tried first and local authentication is used only as a fallback when the RADIUS server is unreachable. This provides both centralized authentication and resilience.
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 radius local
Why this is correct
This command configures AAA authentication for login to first use the RADIUS server group and then fall back to the local database if the RADIUS server is unreachable. The 'local' keyword ensures that local authentication is attempted as a backup, providing resilience.
- ✗
aaa authentication login default group radius enable
Why it's wrong here
Using 'enable' as the fallback method means that if RADIUS is unreachable, the user must enter the enable password to authenticate. This does not use the local username database and may not meet the requirement for local authentication. It also changes the authentication method to privilege level authentication.
- ✗
aaa authentication login default group radius none
Why it's wrong here
The 'none' keyword means that if RADIUS is unreachable, authentication is bypassed entirely, allowing access without credentials. This is insecure and does not provide fallback to local authentication. It would allow unauthorized access if the RADIUS server fails.
- ✗
aaa authentication login default local group radius
Why it's wrong here
This command lists 'local' first, meaning the router will always check the local database before RADIUS. This does not meet the requirement to authenticate against RADIUS first and only fall back to local if the server is unreachable. It effectively bypasses RADIUS for users present locally.
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.
Go deeper
Related to this question
Learn chapter
SDN Controllers and Cisco ACI
Key term
RADIUS vs TACACS+
RADIUS and TACACS+ are two network protocols used to verify user identities and control access to network devices and services, with different approaches to security and flexibility.
Key term
802.1X Authentication
802.1X is a network access control protocol that prevents unauthorized devices from connecting to a wired or wireless network by requiring them to authenticate before gaining access.
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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.