Which native mechanism does OSPF use to prevent loops in MPLS VPNs?

CE devices that run OSPF set the DN bit toward the PE router

PE devices that run OSPF clear the DN bit toward the CE router

CE devices that run OSPF clear the DN bit toward the PE router

Creation of PE to PE OSPF sham link across the MPLS-created super backbone

PE routers verify OSPF domain IDs used by CE OSPF processes

PE devices that run OSPF set the DN bit toward the CE router