Quick Answer
The answer is MP-BGP for VPNv4 route exchange, VRF on PE routers, and MPLS labels for traffic forwarding. These three components form the foundation of an MPLS L3VPN architecture because MP-BGP carries VPNv4 routes with route distinguishers and route targets to ensure end-to-end reachability across the provider backbone, while VRFs on PE routers isolate each customer’s routing table and forwarding plane, enabling multiple tenants to share the same physical infrastructure without overlapping routes. MPLS labels, specifically the inner service label and outer transport label, are then used to forward traffic across the core, separating customer data from provider transport. On the Cisco SPCOR 350-501 exam, this topic tests your understanding of how service providers scale multi-tenant networks; a common trap is confusing MP-BGP with standard BGP or forgetting that VRFs are only on PE routers, not P routers. A useful memory tip is “PE-VPN-MPLS”: PE routers hold VRFs, MP-BGP exchanges VPNv4 routes, and MPLS labels steer the traffic.
This 350-501 practice question tests your understanding of architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which THREE of the following are key components of an MPLS L3VPN architecture? (Choose three.)
RSVP-TE for traffic engineering
Why wrong: RSVP-TE is optional and not a key component of basic L3VPN.
VRF on PE routers
VRF provides per-VPN routing.
LDP for label distribution in the core
LDP is commonly used to distribute labels for the MPLS core.
P routers with full VPN routing tables
Why wrong: P routers have no VPN awareness.
MP-BGP for VPNv4 route exchange
MP-BGP carries VPNv4 routes with route distinguishers.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
VRF on PE routers
VRF (Virtual Routing and Forwarding) on PE routers is a key component because it isolates customer routing tables and forwarding planes within the provider edge, allowing multiple customers to share the same physical infrastructure while maintaining separate routing domains. Each VRF maintains its own routing table, CEF (Cisco Express Forwarding) table, and associated interfaces, which is fundamental to L3VPN separation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
RSVP-TE for traffic engineering
Why it's wrong here
RSVP-TE is optional and not a key component of basic L3VPN.
VRF on PE routers
Why this is correct
VRF provides per-VPN routing.
Related concept
Read the scenario before looking for a memorised answer.
LDP for label distribution in the core
Why this is correct
LDP is commonly used to distribute labels for the MPLS core.
Related concept
Read the scenario before looking for a memorised answer.
P routers with full VPN routing tables
Why it's wrong here
P routers have no VPN awareness.
MP-BGP for VPNv4 route exchange
Why this is correct
MP-BGP carries VPNv4 routes with route distinguishers.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Cisco often tests the misconception that P routers must hold VPN routing information, but in reality P routers only perform label switching and have no awareness of customer VPN prefixes.
Detailed technical explanation
In an MPLS L3VPN, the PE router uses MP-BGP to exchange VPNv4 routes (which include the route distinguisher and route target) with other PEs, while the core P routers simply swap LDP labels for the BGP next hop (the PE loopback). The VRF on the PE imports and exports routes based on Route Target (RT) communities, enabling controlled redistribution between customer sites without leaking into the core.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 350-501 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
The correct answer is: VRF on PE routers — VRF (Virtual Routing and Forwarding) on PE routers is a key component because it isolates customer routing tables and forwarding planes within the provider edge, allowing multiple customers to share the same physical infrastructure while maintaining separate routing domains. Each VRF maintains its own routing table, CEF (Cisco Express Forwarding) table, and associated interfaces, which is fundamental to L3VPN separation.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO of the following are characteristics of MPLS L3VPN architecture? (Choose two.)
mediumWhy B: Option B is correct because in MPLS L3VPN, each customer is assigned a separate Virtual Routing and Forwarding (VRF) instance on the Provider Edge (PE) router. This VRF maintains a unique routing table and forwarding table per customer, ensuring complete isolation between different VPN customers on the same PE.
Last reviewed: Jun 11, 2026
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