350-501 Architecture Practice Question
A service provider is designing a new MPLS L3VPN service. The customer requires that their VPN traffic be isolated from other customers and that the provider edge routers maintain separate routing tables for each VPN. Which architectural component is essential for this separation?
⚠ Common exam trap
Cisco often tests the distinction between data-plane isolation (VLANs, MPLS labels) and control-plane isolation (VRF), and the trap here is that candidates confuse VLAN tagging (Layer 2) with the Layer 3 routing table separation provided by VRFs, assuming VLANs alone can achieve the required routing isolation.
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
✓
VRF (Virtual Routing and Forwarding)
VRF (Virtual Routing and Forwarding) is the essential architectural component that enables a provider edge router to maintain separate, isolated routing tables for each VPN customer. Each VRF instance contains its own routing table, CEF (Cisco Express Forwarding) table, and associated interfaces, ensuring that traffic from one customer is never forwarded using another customer's routing information. This per-VPN isolation is fundamental to MPLS L3VPN services as defined in RFC 4364.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
MPLS label stacking
Why it's wrong here
Label stacking is used for tunneling and traffic engineering, not for per-VPN routing tables.
- ✓
VRF (Virtual Routing and Forwarding)
Why this is correct
VRF creates separate routing tables per VPN instance, enabling isolation.
- ✗
VLAN tagging on the customer-facing interfaces
Why it's wrong here
VLAN provides Layer 2 separation but not separate routing tables.
- ✗
BGP route reflectors
Why it's wrong here
Route reflectors help scale BGP but do not provide per-VPN routing tables.
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