For a Carrier Supporting Carrier (CSC) VPRN where the customer carrier is an ISP that provides Internet connectivity to its end-customers, which of the following is FALSE?

The fundamental purpose of a Carrier Supporting Carrier (CSC) VPRN is for the backbone carrier to provide transparent IP transport between the customer carrier's sites (Points of Presence). The customer carrier's PE routers (which are the CSC-CEs from the backbone's perspective) establish routing adjacencies with the backbone's PE routers (CSC-PEs). The backbone network then uses MP-BGP to distribute the customer carrier's routes between the CSC-PEs. This architecture obviates the need for the customer carrier's PE routers at different sites to have direct routing adjacencies (like a full mesh of eBGP sessions) with each other. The backbone network handles the inter-site connectivity.

A. The backbone carrier provisions a single VPRN service instance (a single VRF) to connect all sites of the customer carrier, making this statement true.
C. The customer carrier can operate a standard IP/IGP network, relying on the CSC VPRN service for inter-site connectivity, without needing its own MPLS core.
D. The customer carrier, being an ISP, can run MPLS in its own network to offer services to its end-customers, which is a common hierarchical VPN model that enhances scalability.

1. Nokia 7450 ESS, 7750 SR, 7950 XRS, and VSR Layer 3 Services Guide: VPRN, Release 22.10.R1, Section: "Carrier-of-Carriers VPRN".

Page 103: "The carrier-of-carriers option allows an ISP... to provide VPN services to its own customers... The customer is the carrier and the carrier's customers are the end-customers." This confirms the scenario.

Page 104 (Figure 13): The architectural diagram clearly shows CSC-CE routers peering with CSC-PE routers, and no direct peering between CSC-CE routers at different sites. The MP-BGP sessions exist only between the CSC-PEs in the backbone. This directly refutes option B.

Page 104: "The customer carrier can run MPLS in its network and provide MPLS VPN services to its customers. In this case, the PEs of the customer carrier do not need to hold all the Internet routes." This confirms that option D is a valid and common scenario.

2. RFC 4364: BGP/MPLS IP Virtual Private Networks (VPNs), Section 10: "Carrier's Carrier".

Page 31: "The backbone carrier's PEs which attach to the customer carrier's networks are known as the 'CSC-PEs'... The customer carrier's routers which attach to the CSC-PEs are known as the 'CSC-CEs'."

Page 32: "The CSC-CEs do not need to be BGP speakers... If the CSC-CEs are BGP speakers, they can peer with the CSC-PEs." This section details the peering relationship is between CSC-CE and CSC-PE, not between different CSC-CEs across the backbone.