MPLS L3VPN PE Router VPNv4 Translation

300-410 By islever Editorial Last updated

Describe MPLS Layer 3 VPN

Short answer

D The Provider Edge (PE) router translates customer routing information into VPNv4 routes to exchange them with other devices through MP-BGP.

Question

Which router translates the customer routing information into VPNv4 routes to exchange VPNv4 routes with other devices through MP-BGP?
  1. VPNv4 RR
  2. P
  3. CE
  4. PE Correct Answer

Key Takeaways

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.

Common mistake: 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.

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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Community Votes

D
100%

100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 4 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 4

  1. Defilet 👍 4 Answered D
    The router that translates the customer routing information into VPNv4 routes to exchange VPNv4 routes with other devices through MP-BGP is the Provider Edge (PE) router
  2. 9410480 👍 4 Answered D
    The key is "Translates the customer". Answer is D.
  3. cloud29 👍 2 Answered A
    The router that translates the customer routing information into VPNv4 routes to exchange VPNv4 routes with other devices through MP-BGP is the Provider Edge (PE) router1. So, the correct answer is D. PE. The PE router exchanges routing updates with the Customer Edge (CE) device, translates the CE routing information into VPNv4 routes, and exchanges these VPNv4 routes with other PE devices through the Multiprotocol Border Gateway Protocol (MP-BGP)1.
  4. dapardo 👍 3 Answered D
    Correct answer is D

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