What are OSPF Stub Areas, Totally Stubby Areas, and Not-So-Stubby Areas?

Stubs are used to reduce the size of the routing table in a network & A stub area is the most basic form of the “stubbie” area types. It prevents any external route from entering into the area’s database. A  Totally stub not only block any external route from entering into the database but they also block any inter-area routes from entering the area. This reduces the size of the database even further, where as Not so stubby area (NSSA) are very similar to stub area’s with 1 major addition. NSSA area’s only block external routes from other area’s from entering into the database. The NSSA area’s however do allow for local redistribution using the special NSSA external route.