OSPF areas

Stub area:
* filters Type 5 LSAs
* default route is inserted into routing table on all routers in Stubby area
* E1/E2 routes are removed from routing table on all routers in Stubby area
* there can only be one exit point out of this area
* no external routes cannot be learned via Stubby area and then inserted into all OSPF areas (because LSA Type 5 is filtered in Stubby area)

Totally Stubby area:
* filters Type 3, 4, 5 LSAs
* default route is inserted into routing table on all routers in Totally Stubby area
* E1/E2 routes are removed from routing table on all routers in Totally Stubby area
* IA routes are removed from routing table on all routers in Totally Stubby area
* there can only be one exit point out of this area
* no external routes cannot be learned via Totally Stubby area and then inserted into all OSPF areas (because LSA Type 5 is filtered in Stubby area)

Not So Stubby area:
* filters Type 5 LSAs but permits Type 7 LSAs to pass through NSSA and once they reach backbone area they are converted back into Type 5 LSAs
* default route is inserted into routing table on all routers in NSSA
* E1/E2 routes are removed from routing table on all routers in NSSA
* external routes can be learned via NSSA and then inserted into all OSPF areas


Not So Stubby Totally Stubby area:
* filters Type 3,4, 5 LSAs but permits Type 7 LSAs to pass through Not So Stubby Totally Stubby area and once they reach backbone area they are converted back into Type 5 LSAs
* default route is inserted into routing table on all routers in Not So Stubby Totally Stubby area
* E1/E2 routes are removed from routing table on all routers in Not So Stubby Totally Stubby area
* IA routes are removed from routing table on all routers in Not So Stubby Totally Stubby area
* external routes can be learned via Not So Stubby Totally Stubby area and then inserted into all OSPF areas