350-501 Architecture Practice Question
Which THREE of the following are required components for implementing MPLS Layer 3 VPN (L3VPN) in a service provider network? (Choose three.)
⚠ Common exam trap
Cisco often tests the misconception that P routers require VRF configuration or that IBGP is used for label distribution between PE and P routers, when in fact P routers only need MPLS forwarding and LDP for label exchange.
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
✓
MP-BGP between PE routers to exchange VPNv4 routes
MP-BGP (Multiprotocol BGP) is essential for carrying VPNv4 routes between PE routers. It uses address family VPNv4 to transport customer IPv4 prefixes along with their Route Distinguisher (RD) and Route Target (RT) attributes, enabling the separation and distribution of multiple customer VPNs across the MPLS core.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
MP-BGP between PE routers to exchange VPNv4 routes
Why this is correct
MP-BGP between PE routers is mandatory for MPLS L3VPN because it carries VPNv4 routes that include both the IPv4 prefix and the Route Distinguisher, enabling unique global identification of overlapping customer address spaces. This satisfies the requirement for a control-plane protocol that can separate and distribute per-VPN routing information across the provider backbone.
- ✓
VRF configuration on PE routers to separate customer routes
Why this is correct
VRFs create separate routing tables per customer on the PE.
- ✓
MPLS forwarding enabled on all core routers
Why this is correct
MPLS is required to forward labeled packets across the core.
- ✗
IBGP between PE and P routers for label distribution
Why it's wrong here
Label distribution uses LDP, not BGP.
- ✗
VRF configuration on P routers
Why it's wrong here
P routers only forward MPLS packets; they do not need VRFs.
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
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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.