OSPF Area Blocking LSA Types 3, 4, and 5, Allowing Default Summary Route

D.

The OSPF protocol uses Link State Advertisements (LSAs) to communicate routing information between routers within an OSPF domain. There are several types of LSAs used by OSPF, including LSA Type 1 (Router LSA), LSA Type 2 (Network LSA), LSA Type 3 (Summary LSA), LSA Type 4 (ASBR Summary LSA), and LSA Type 5 (AS External LSA).

In OSPF, an area is a logical grouping of routers that share the same characteristics and routing policies. OSPF areas are identified by a 32-bit number called an Area ID. Each OSPF domain must have at least one backbone area (Area 0) and may have one or more non-backbone areas.

To control the flow of routing information between OSPF areas, OSPF uses several types of area types. These area types include normal areas, stub areas, not-so-stubby areas (NSSAs), and totally stubby areas.

Of these area types, the totally stubby area blocks LSA Type 3, 4, and 5 from being propagated into the area. This means that routers within the totally stubby area will only have knowledge of routes within their own area and any default routes that are configured.

However, unlike the stub area, the totally stubby area does allow a default summary route to be advertised into the area. This default route is generated by the Area Border Router (ABR) and is used by routers within the totally stubby area to reach destinations outside of the OSPF domain.

In summary, the OSPF area that blocks LSA Type 3, 4, and 5 but allows a default summary route is the totally stubby area.