ABR-Generated LSA Types in Totally Stub Area

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A stub area that only allows routes internal to the area and restricts Type 3 LSAs from entering the stub area is often called a totally stubby area.

Totally stubby areas can only contain type 1 and 2 LSAs, and a single type 3 LSA.

In a totally stubby area, the ABR (Area Border Router) generates and sends only two types of LSAs:

1. Type 3 Summary LSA: An ABR generates type 3 summary LSAs to advertise the summary routes from other areas into a totally stubby area. Type 3 LSAs are also known as summary LSAs, as they summarize the routes from other areas that are not present in the totally stubby area.

2. Type 1 Router LSA: An ABR generates type 1 router LSAs to describe the routers connected to the network and their interfaces. These LSAs are necessary for the correct operation of OSPF, as they enable the calculation of the shortest path tree.

Therefore, the correct answer to the question is D. Type 3 LSA and A. Type 2 LSA is not sent in totally stubby area.

Type 4 LSAs are known as ASBR-Summary LSAs and are generated by an ABR to advertise the external routes to other areas. However, they are not generated or sent in a totally stubby area.

Type 5 LSAs are known as Autonomous System External LSAs and are generated by ASBRs (Autonomous System Boundary Routers) to advertise external routes outside the OSPF domain. However, they are not sent in a totally stubby area.

In summary, an ABR generates and sends only two types of LSAs in a totally stubby area: type 3 summary LSAs and type 1 router LSAs.