MPLS L3VPN PE Router VPNv4 Translation
Which router translates the customer routing information into VPNv4 routes to exchange VPNv4 routes with other devices through MP-BGP?
Community Votes
100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
The key trap is confusing the PE with other MPLS roles; only the PE handles the translation from customer-specific IPv4 prefixes to global VPNv4 addresses.
This question tests the role of the Provider Edge (PE) router in MPLS Layer 3 VPN architectures, specifically its function in translating customer routing information into VPNv4 routes for MP-BGP exchange.
Candidates often confuse the PE with the P (Provider) router or CE (Customer Edge), failing to recognize that the PE is the specific boundary device performing address translation and VRF separation.
Community Discussion (4 comments)
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Expert Analysis
Why the Answer Is Correct
The Provider Edge (PE) router is the critical component in an MPLS Layer 3 VPN architecture that interfaces directly with Customer Edge (CE) devices. It receives customer routing updates (typically standard IPv4) via local routing protocols like OSPF or EIGRP. The PE router then translates these customer-specific routes into VPNv4 routes by adding a Route Distinguisher (RD) to the prefix, making them unique across the provider network. These VPNv4 routes are subsequently exchanged between PE routers using Multiprotocol BGP (MP-BGP). Therefore, the PE is the only device that performs this specific translation and MP-BGP exchange function.Why the Other Options Are Wrong
Option A (VPNv4 RR) refers to a Route Reflector used within the MPLS core to optimize BGP peering among PEs; it does not translate customer routes but rather reflects existing VPNv4 routes. Option B (P) refers to the Provider router, which exists solely within the service provider's core network. P routers forward traffic based on the outermost MPLS label and do not have direct connectivity to CE devices nor do they participate in MP-BGP exchanges for customer routes. Option C (CE) represents the customer's own router, which sends standard unicast IPv4 routes to the PE and does not handle VPNv4 addressing or MP-BGP.Community Comment Notes
Community consensus strongly supports option D, with multiple users highlighting the keyword "translates" as the decisive factor. As user 9410480 noted, "The key is 'Translates the customer'. Answer is D." Another user, Defilet, clarified that "The router that translates the customer routing information... is the Provider Edge (PE) router." This aligns perfectly with Cisco's official documentation on MPLS L3VPN operations.Exam Strategy
When analyzing MPLS L3VPN questions, always identify the boundary devices first. Remember: CE connects to PE, PE connects to P and other PEs. Only the PE interacts with the customer's unicast routes and translates them into the provider's VPNv4 domain.
Frequently Asked Questions
Why doesn't the P router translate routes?
The P router is part of the core and only forwards based on MPLS labels. It has no visibility into customer VRFs or IP prefixes.
What is the purpose of the Route Distinguisher?
The RD is added by the PE router to make customer IPv4 prefixes unique globally, allowing overlapping IP spaces from different customers to coexist in the VPNv4 address space.
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