350-501 Security and Services Practice Question
A BNG (Broadband Network Gateway) is used for subscriber management. Which protocol is typically used between the BNG and the subscriber's modem (CPE) for authentication and IP address assignment in a PPPoE environment?
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
✓
PPPoE with PPP authentication and IPCP
In a PPPoE environment, the BNG acts as the access concentrator. Authentication is performed using PAP or CHAP, and IP address assignment is done via IPCP (IP Control Protocol). The BNG also uses RADIUS for centralized authentication but between BNG and CPE, PPPoE uses PPP for authentication and IPCP for IP address.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
DHCP
Why it's wrong here
DHCP is used in IPoE environments, not PPPoE.
- ✗
RADIUS directly to CPE
Why it's wrong here
RADIUS is between BNG and AAA server, not directly to CPE.
- ✗
L2TP
Why it's wrong here
L2TP is a tunneling protocol, not for subscriber authentication.
- ✓
PPPoE with PPP authentication and IPCP
Why this is correct
PPPoE uses PPP for authentication and IPCP for IP address assignment.
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.