Open Shortest Path First Version 2 (OSPFv2) is a link-state routing protocol that uses link-state advertisements (LSAs) to update neighboring routers about a router‘s interfaces. Each router maintains an identical area-topology database to determine the shortest path to any neighboring router.
OSPF is built upon a hierarchy of network components and areas. The highest level of the hierarchy is the autonomous system. An autonomous system is defined as a number of networks, all of which share the same routing and administration characteristics. A backbone area forms the core of the network, connecting all other areas.
Details of these and other OSPF components are provided in OSPFv2 SLX topics.
Refer on how to set the DN bit during MP-BGP redistribution 1 into OSPF .