In a VPRN (MPLS L3VPN), Multi-Protocol BGP (MP-BGP) is used to distribute customer VPN routes across the provider's core network. These routes are exchanged between Provider Edge (PE) routers as VPN-IPv4 prefixes. To ensure that all PEs participating in a VPRN learn the routes from all other PEs in the same VPRN, a logical full mesh of internal BGP (iBGP) sessions is required between them. This allows a route learned from a Customer Edge (CE) device at one PE to be advertised to all other remote PEs, providing full connectivity for the customer's sites. While route reflectors can be used to simplify the physical configuration, the logical topology remains a full mesh where every PE can exchange routes with every other PE.

A. Full mesh between all CE, PE and P devices: P (Provider) routers are typically not BGP-aware and do not participate in VPRN routing; they only perform label switching. CEs do not peer with P routers.

B. Full mesh between PE and P devices: P routers do not run BGP for VPRN services. BGP sessions for route distribution are established between PE routers, not with P routers.

C. Full mesh of P devices: P routers are part of the transport core and are not involved in BGP peering for VPRN route exchange.

E. Full mesh between PE and CE devices: A CE device only needs a BGP session with its directly connected PE(s). There is no requirement for a full mesh between all CEs and all PEs.

1. Nokia 7750 SR OS Services Guide, Release 21.10.R1: In the "VPRN Service Overview" section, under "Distributing VPN-IPv4 Addresses", the documentation states: "To distribute VPN routing information across the service provider's network, PE routers must be configured to establish BGP sessions with other PE routers. A full mesh of iBGP sessions must be established between all PE routers, or a route reflector must be used." (Document ID: 3HE 17194 AAAC TQZZA, Section: VPRN Service Overview). This directly confirms the requirement for a full mesh of PE devices.

2. Rosen, E., & Rekhter, Y. (2006). BGP/MPLS IP Virtual Private Networks (VPNs). RFC 4364. Section 4, "Distributing VPN-IPv4 Information", describes the BGP mechanisms. It states, "If a set of PEs are in the same AS, they may be fully meshed, or they may use BGP route reflectors to distribute VPN-IPv4 routes." This foundational IETF standard establishes the logical full-mesh requirement (or its RR-based equivalent) between PEs in the same Autonomous System. (Available at: https://doi.org/10.17487/RFC4364)