In OSPF there are many area types:
Stub area : will block external routes LSA type 5, but allow inter area routes LSA type 3 and 4 and injects default route
Totally Stub area: Block External as well as Inter area routes, and inject default route.
Well if I understand the purpose of creating the above areas is kind of reducing the size of the routing table. if that's the case why not just use the Totally Stub area and that will do the job ? I mean without worrying about creating the stub area .
OSPF also has NSSA and NSSA totally stub, when do we need these areas ? I know that NSSA when receiving the redistributed external routes it will mark them as Type 7, then the ABR will convert them to type 5 LSA, but what purpose it serves if it does not reduce the size of the routing table ? Type 7 or Type5 will not reduce the size if I understand..