OSPF Areas

OSPF uses a hierarchical network design based on areas to improve scalability and reduce routing table size. Each area has its own link-state database.

Types of OSPF Areas:

  • Backbone Area (Area 0): The central area to which all other areas must connect. It distributes routing information between non-backbone areas.
  • Standard Area: An area that can carry all types of LSA traffic and connect to the backbone area.
  • Stub Area: An area that does not accept external routes (Type 5 LSAs) from outside the OSPF domain. It relies on a default route to reach external destinations.
  • Totally Stubby Area (TSA): An extension of a stub area that does not accept external routes (Type 5 LSAs) or summary routes (Type 3 LSAs) from other OSPF areas. It only accepts a default route.
  • Not-So-Stubby Area (NSSA): A type of stub area that can import external routes into the OSPF domain using Type 7 LSAs, which are then translated into Type 5 LSAs by the NSSA ABR.