VCL-WIKI
OSPF Areas

OSPF defines several area types:

1. Backbone
2. Non-Backbone/regular
3. Stub
4. Totally stubby
5. Not-so-stubby
6. Transit.

1. Backbone area: The backbone area (also known as area 0 or area 0.0.0.0) is the core of an OSPF network. All other areas are connected to it, either directly or through other routers. All OSPF areas must connect to the backbone area.
2. Regular area: A regular area is a non-backbone (nonzero) area without specific feature of generating and receiving summary and external LSAs.
3. Transit area: A transit area is the area with two or more OSPF border routers and is used to pass network traffic from one adjacent area to another.
4. Stub area: A stub area is an area that does not receive route advertisements external to the AS and routing from within the area is based entirely on a default route.
5. Totally stubby area: This area does not allow summary routes in addition to not having external routes, that is, inter-area routes are not summarized into totally stubby areas.
6. Not-so-stubby area: It can import autonomous system external routes and send them to other areas, but cannot receive AS-external routes from other areas.

The above mentioned features are offered and supported by VCL-MX-50xx family of IP/MPLS Routers.