In an MPLS VPN architecture, a P (Provider) router's role is to perform high-speed packet forwarding based on MPLS labels, a process known as label switching. When a customer packet traverses the provider core, it is encapsulated with at least one MPLS label (the transport label). The P router makes its forwarding decision solely based on this transport label, which identifies the path to the egress PE router. The P router never inspects the customer's IP packet header and is therefore completely unaware of the customer's IP routes. This design is fundamental to the scalability of MPLS VPNs, as it keeps the provider core free from carrying extensive customer routing information.

B. The ingress PE router must have a route to the customer's destination in the appropriate VRF to determine the BGP next-hop (egress PE) and assign the correct VPN label.

C. The egress PE router must have a route to the customer's destination in the appropriate VRF to perform the final IP lookup and forward the packet to the correct customer site.

D. This statement is incorrect because, as explained, both ingress and egress PE routers require specific customer routes to function, whereas P routers do not.

1. Nokia 7750 SR OS Services Architecture Guide, Release 22.10.R1, "VPRN Services" chapter, section "Packet Flow for a VPRN Service": This guide details the packet walkthrough. It states, "The P-router receives the packet and, based on the top label, it swaps the label and forwards the packet to the next-hop P-router or the egress PE-router." This confirms the P router operates only on the transport label, not the customer's destination IP address.

2. RFC 4364: BGP/MPLS IP Virtual Private Networks (VPNs), Section 4.1, "Forwarding": This foundational IETF standard specifies the architecture. It states, "The 'P-routers' (provider routers that are not PE-routers) are not aware of the VPN routes. They forward packets to the egress PE-router by switching labels. The ingress PE-router must know which label to use when sending a packet to an egress PE-router." (Page 7). This directly supports that P routers do not have customer routes.

3. Nokia Virtual Private Routed Network (VPRN) Configuration Example, Section "VPRN Overview": This document illustrates the roles, stating, "The P routers in the core of the provider's network are not aware of the VPN routes. When a P router receives a packet from a PE router, it uses the MPLS label to forward the packet to the proper PE router." This reinforces the concept of a customer-route-free core.