Which statement describes the default Junos OS behavior for OSPF?

The statement reflecting the default behavior of the Junos OS for OSPF is that an ABR (Area Border Router) does not announce a default route into a stub area. In OSPF, stub areas are designed to suppress external route advertisements, which include routes to external networks (NSSA) and inter-area routes. The primary purpose of a stub area is to reduce the amount of routing information exchanged and to maintain a simpler routing table within the area.

In a stub area, routers will have a simplified view of the network, and the default route (0.0.0.0) can be configured to be injected by the ABR. However, the default behavior without special configuration is for the ABR to not provide a default route into the stub area, maintaining the integrity and simplicity of routing within that area. This is in accordance with the OSPF standards governing stub area functionality.

The other options suggest behaviors that conflict with the principles of OSPF's stub area configurations. For instance, external LSAs being advertised contradicts the purpose of a stub area, which aims to suppress such advertisements. Stub area internal routers do not naturally generate a default route unless configured specifically for this purpose, which is not the default behavior in