Refer to the exhibit. Service Provider A has offered to help Service Provider B to provide local connectivity for a customer who has a business operation in North America and recently opened an office

Carrier Supporting Carrier is used when a customer carrier runs its own MPLS network over the service provider backbone, which does not apply to two peer SPs jointly delivering a shared L3VPN service.

eBGP VPNv4 multihop between route reflectors (Inter-AS Option C) requires the exchange of labeled VPNv4 routes between distant RRs and demands a high degree of trust and complex configuration that is inappropriate when the two SPs have no prior relationship.

Back-to-back VRF (Inter-AS Option A) connects the two providers by placing the customer VPN in a dedicated VRF on each ASBR and interconnecting those VRFs via a routed interface with route redistribution. No MPLS labels or VPNv4 routes are exchanged across the SP boundary, which maximizes security by limiting the routing information each provider must expose to the other. Because the interconnect appears as a standard routed link, no pre-existing BGP VPNv4 trust relationship or shared label space is required.

VPNv4 peering between ASBRs (Inter-AS Option B) requires the ASBRs to maintain and redistribute all VPNv4 routes from the peer AS, exposing full customer routing information across the inter-AS link and increasing both complexity and security risk.