Which protocol carries labeled paths between PE routers in an MPLS network?

MP-BGP (Multiprotocol BGP) is correct because it extends BGP to carry reachability information for different network layer protocols, including labeled VPN routes (VPNv4 or VPNv6) between PE routers in an MPLS VPN. This allows PE routers to exchange VPN routes and their associated labels, forming the labeled paths across the MPLS backbone. LDP (Label Distribution Protocol) is incorrect because it distributes labels for IP prefixes within an MPLS domain, not for labeled VPN paths between PE routers. RSVP (Resource Reservation Protocol) is incorrect because it is used for traffic engineering and reserving bandwidth, not for distributing VPN labels. IGP (Interior Gateway Protocol) is incorrect because it handles routing within an autonomous system and does not carry labeled VPN paths.