350-501 Security and Services Practice Question
Which protocol is used by a BNG to authenticate and authorize subscribers?
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
✓
RADIUS
BNG uses RADIUS for AAA (authentication, authorization, and accounting) of subscribers. RADIUS exchanges messages with a backend server to validate credentials and assign policies.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
RADIUS
Why this is correct
RADIUS is the standard for subscriber authentication in BNG.
- ✗
DIAMETER
Why it's wrong here
DIAMETER is used in LTE/IMS, not typically in BNG.
- ✗
LDAP
Why it's wrong here
LDAP is a directory protocol, not typically used for BNG authentication.
- ✗
TACACS+
Why it's wrong here
TACACS+ is primarily for device administration, not subscriber management.
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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-501 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 350-501 exam.