Which OSPF area type allows external routes to be flooded by ASBRs within its own area?

The OSPF area type that allows external routes to be flooded by ASBRs (Autonomous System Boundary Routers) within its own area is the not-so-stubby area (NSSA). A not-so-stubby area is designed to allow external routes, specifically Type 7 LSAs, which contain information about external networks that are redistributed into OSPF by ASBRs, while still maintaining some of the restrictions of a stub area.

In a not-so-stubby area, ASBRs can originate external routing information into the NSSA, which allows this information to be shared within the area but does not allow it to be exported to the backbone area using Type 5 LSAs. This specific design promotes optimization of route distribution and helps manage routing information within OSPF more effectively.

Other area types, such as stub areas and the backbone area, do not permit the same level of external route distribution. Stub areas do not allow external routes at all, while a backbone area facilitates the transport of these routes but does not actually define how external routes are brought in from ASBRs like a not-so-stubby area does. Thus, the not-so-stubby area serves a unique function in OSPF by balancing route management and external