A service provider runs an MPLS L3VPN for a customer that uses OSPF as the PE-CE routing protocol at two sites, Site A and Site B. Both sites also have a direct backdoor OSPF link between them within the same OSPF area. The customer complains that traffic between the two sites always takes the low-speed backdoor link instead of the high-speed MPLS backbone. The PEs redistribute customer routes into MP-BGP and back into OSPF as type-3 inter-area routes. What must the SP engineer configure to make the MPLS backbone the preferred path?