OSPF area
termA group of OSPF networks and routers that shares one link-state database, its topology hidden from the rest of the domain.
Areas bound flooding and computation: routers inside an area know its full map, routers outside see only summaries. Area 0 is the backbone that carries traffic between areas, and stub and not-so-stubby areas (NSSAs) change which external routes enter an area.
RFC 2328 gives the backbone, area 0.0.0.0, three duties: it contains every area border router, carries routing between non-backbone areas, and must be contiguous, if need be through virtual links configured across a non-backbone area. Inter-area routing therefore takes the shape of a star with the backbone as hub. If the backbone partitions, parts of the AS become unreachable; a non-backbone area that partitions simply becomes two areas.
A stub area receives no AS-external-LSAs; its routers reach external destinations through a default summary from the border router, which shrinks their database. It suits an area with a single exit, cannot carry a virtual link and cannot contain an AS boundary router. Totally stubby is industry usage for a stub whose border routers also withhold most summaries, FRRouting's stub no-summary. An NSSA, defined in RFC 3101, does the opposite of shrinking: it may import external routes as type 7 LSAs, which its border routers translate into type 5.
Neighbours must agree on the area ID and on the stub or NSSA flag carried in their Hellos, or the adjacency never forms.
Also known as: area 0, backbone area, stub area, nssa, not-so-stubby area, totally stubby area