In a Carrier Supporting Carrier (CSC) VPRN, which of the following is NOT a benefit to the network provider?

The Carrier Supporting Carrier (CSC) VPRN model is designed to scale by isolating the backbone provider from the routing and service complexity of its customer carriers. The backbone provider is shielded from the explosion in the number of end-customer routes and VPNs, as these are managed entirely by the customer carrier. However, the backbone provider must create a separate VPRN instance (a VRF) for each customer carrier it services. Therefore, as the number of customer carriers increases, the number of VRFs and associated BGP sessions on the backbone PE routers (CSC-PEs) grows linearly. This directly consumes resources and adds configuration overhead, making it a scaling consideration rather than an inherent scaling benefit of the architecture.

A. This is a primary benefit. The backbone provider is unaware of the individual VPNs offered by the customer carrier, so the solution scales independently of this factor.

B. This is a core benefit. The backbone provider only carries routes for the customer carrier's infrastructure, not the vast number of routes from the end-customers.

C. This is an operational benefit. The backbone provider's responsibility ends with providing transport to the customer carrier, who in turn manages all end-customer services.

1. RFC 4364: BGP/MPLS IP Virtual Private Networks (VPNs)

Section 10, "Carrier's Carrier": This section details the CSC architecture. It states, "The backbone carrier's PE router that is attached to the customer carrier's network maintains a VRF for that customer carrier's network." This confirms that each customer carrier requires a dedicated VRF, directly linking the number of carriers to the state on the backbone PE. It also states, "The number of routes in the backbone carrier's P-routers and PE-routers is independent of the number of VPN customers and the number of destinations in the VPNs," which validates that options A and B are key benefits.

2. Nokia 7750 SR OS Services Guide, Release 21.10.R1

Section: VPRN Carrier Supporting Carrier: The guide explains, "A VPRN is created on the backbone provider PE router for each customer carrier." This explicitly states the one-to-one relationship between customer carriers and VPRN instances on the backbone network, supporting the reasoning that scaling by the number of carriers is a direct resource consideration, not a benefit. It also notes, "The backbone VPRN provider does not need to know the end-customer’s routes," confirming the benefits listed in options A and B.