OSPF Stub Areas
OSPF allows for different area types to control the propagation of routing information, reducing routing table size and improving scalability. Stub areas are designed to minimize the amount of routing information within an area.
Stub Area:
- Does not allow Type 5 LSAs (external routes) to be flooded into the area.
- An ABR in a stub area injects a default route (0.0.0.0) as a Type 3 LSA into the stub area.
- Configuration:
area [area-id] stub
Totally Stubby Area (Cisco Proprietary):
- Does not allow Type 5 LSAs or Type 3 LSAs (summary routes) to be flooded into the area.
- An ABR in a totally stubby area injects only a default route (0.0.0.0) as a Type 3 LSA.
- Configuration:
area [area-id] stub no-summary
Not-So-Stubby Area (NSSA):
- Allows the injection of external routes into the NSSA via a Type 7 LSA.
- Type 7 LSAs are translated into Type 5 LSAs by the NSSA ABR when flooded to other areas (including the backbone).
- Configuration:
area [area-id] nssa