350-501 Security and Services Practice Question
A service provider is deploying a BNG for subscriber management. Which protocol is used to authenticate subscribers and assign IP addresses via the BNG?
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 typically uses RADIUS for authentication, authorization, and accounting of subscribers. DHCP server functionality on BNG assigns IP addresses, but authentication is via RADIUS.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
PPPoE only
Why it's wrong here
PPPoE is an encapsulation, not an authentication protocol; it often uses RADIUS.
- ✗
LDAP
Why it's wrong here
LDAP is not typically used directly for BNG subscriber authentication.
- ✗
TACACS+
Why it's wrong here
TACACS+ is used for device management, not subscriber authentication.
- ✓
RADIUS
Why this is correct
RADIUS enables the BNG to authenticate subscribers against a central AAA server and dynamically assign IP addresses via DHCP or PPPoE session attributes. This satisfies the stem’s requirement for a protocol that both verifies subscriber credentials and delivers IP configuration, whereas alternatives like DHCP alone lack authentication, and TACACS+ does not handle IP address assignment.
Visual reference
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.