A large enterprise network has two data centers and a WAN edge in a hub-and-spoke network topology. The entire network is in a single OSPF area. Spoke routers are connected to unreliable WAN links. Wh

ASBRs redistribute external routes into OSPF but have no function in filtering LSAs between OSPF areas; inter-area LSA filtering is an ABR responsibility.

Spoke routers in normal areas receive all LSA types with no filtering applied, which is the exact opposite of the desired behavior for unreliable WAN links.

Hub routers must be configured as ABRs because only an ABR sits at an area boundary and has the authority to suppress summary and external LSAs from entering an attached stub or totally stubby area.

Totally stubby areas instruct the ABR to block all Type 3 inter-area, Type 4 ASBR summary, and Type 5 external LSAs from flooding into the area, replacing them with a single default route - providing maximum LSA filtering ideal for spoke routers on unreliable WAN links.

Stub areas only block Type 5 external LSAs while still allowing Type 3 inter-area summary LSAs to flood in, providing less filtering than totally stubby areas and leaving spoke routers with larger LSDBs.