5.4 Stub and Totally Stubby Areas
5.4.1 Using stub and totally stubby areas
You can configure an OSPF router interface to either operate in a stub area (does not accept information about routes external to the AS) or as a totally stubby area (does not accept external AS routes and summary routes from other areas internal to the AS). Both of these area types are shown in the figure.

By configuring an area as stub, you can greatly reduce the size of the link-state database inside that area and, as a result, reduce the memory requirements of area routers. Remember that stub areas do not accept Type 5 (that is, external) LSAs.

Because OSPF routers internal to a stub area will not learn about external networks, routing to the outside world is based on a 0.0.0.0/0 default route. When you configure a stub area, the stub's ABR automatically propagates a 0.0.0.0/0 default route within the area.

Stub areas are typically created when you have a hub-and-spoke topology, with the spokes (such as branch offices) configured as stub areas. In the case of a hub-and-spoke topology, the branch office may not need to know about every network at the headquarters site. It can instead use a default route to get there.

To further reduce the number of routes in a table, you can create a totally stubby area, which is a Cisco-specific feature. A totally stubby area is a stub area that blocks external Type 5 LSAs and summary (that is, Type 3 and Type 4) LSAs from entering the area. This way, intra-area routes and the default of 0.0.0.0/0 are the only routes known to the stub area. ABRs inject the default summary link 0.0.0.0/0 into the totally stubby area. 

Thus, totally stubby areas further minimize routing information and increase stability and scalability of OSPF internetworks. This is typically a better solution than creating stub areas, unless the target area uses a mix of Cisco and non-Cisco routers. The following sections describe the criteria for determining whether an area should be configured as stub or totally stubby, and the configuration commands necessary to implement these area types.