300-410 Infrastructure Security Practice Question
A network administrator is configuring AAA on a Cisco IOS router. The administrator wants to use a RADIUS server for authentication and authorization, but wants to use local authentication as a fallback if the RADIUS server is unreachable. Which command should be used to configure the fallback?
⚠ Common exam trap
The trap here is reversing the order of methods or using 'enable' or 'none' as fallback, which do not provide local authentication 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 command 'aaa authentication login default group radius local' sets RADIUS as the primary authentication method and local as the fallback. If the RADIUS server is unreachable, the router will use the local username database, ensuring continued administrative access.
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 enable
Why it's wrong here
This command uses the enable password as a fallback instead of local authentication. The enable password is not the same as local username/password authentication and may not provide the desired fallback to the local user database. It is less secure and not the intended fallback.
- ✗
aaa authentication login default local group radius
Why it's wrong here
This command uses local authentication first, then RADIUS. The administrator wants RADIUS as primary and local as fallback, so the order is reversed. Using local first would bypass RADIUS for all logins, which is not the desired configuration.
- ✗
aaa authentication login default group radius none
Why it's wrong here
This command uses RADIUS first, and if it fails, no authentication is required (none). This is highly insecure and does not provide a fallback to local authentication. It would allow access without credentials if RADIUS is unreachable.
- ✓
aaa authentication login default group radius local
Why this is correct
This command configures the default login authentication method list to use RADIUS first, then local authentication if RADIUS is unreachable. It provides the desired fallback to local authentication, ensuring administrative access is maintained even if the RADIUS server fails.
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
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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.