Quick Answer

The answer is MP-BGP with the VPNv4 address family, as this is the only technology capable of carrying the extended community attributes and route distinguishers needed to exchange VPN routes between the provider carrier and the customer carrier in a carrier-supporting carrier (CSC) architecture. In CSC, the customer carrier runs its own MPLS network, but it must still learn the provider carrier’s VPN routes to enable end-to-end connectivity; MP-BGP with the VPNv4 address family handles this by advertising labeled VPN-IPv4 prefixes across the provider-carrier boundary. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of hierarchical MPLS VPNs and the role of MP-BGP in separating routing domains—a common trap is assuming IPv4 BGP or an IGP like OSPF can carry VPN routes, but they lack the necessary VPN-specific attributes. A helpful memory tip: think of MP-BGP as the “multiprotocol bridge” that carries VPNv4 routes across carrier boundaries, while IGPs only handle internal reachability.