OSPFv3 area types

OSPFv3 is built upon a hierarchy of network areas. All areas for a given OSPFv3 domain reside in the same AS. An AS is defined as a number of contiguous networks, all of which share the same interior gateway routing protocol.

An AS can be divided into multiple areas, including the backbone (area 0). Because each area represents a collection of contiguous networks and hosts, the topology of a given area is not known by the internal routers in any other area. Areas define the boundaries to which router-LSAs and network-LSAs are broadcast. This limits the amount of LSA flooding that occurs within the AS and also helps to control the size of the link-state databases (LSDBs) maintained in OSPFv3 routers. An area is represented in OSPFv3 by either a 32-bit dotted-decimal address or a number. Area types include:
  • Backbone

  • Normal

  • Not-so-stubby (NSSA)

  • Stub

All areas in an AS must connect with the backbone through one or more ABRs. If a normal area is not directly connected to the backbone area, it must be configured with a virtual link to an ABR that is directly connected to the backbone. The stub and NSSA area types do not allow virtual link connections to the backbone area.
Example of an AS with multiple areas and external routes