Router B: OSPF Router in Totally Stub Area - Suppressed LSAs

Suppression of LSAs in Totally Stub Area | Router B | JN0-360

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Question

Router B is an OSPF router connected to both Area 0 and Area 2. Area 2 has been configured as a totally stubby area. Which three LSA types does Router B suppress from Area 2? (Choose four.)

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Explanations

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Router B is a router in OSPF that is connected to both Area 0 and Area 2, and Area 2 has been configured as a totally stubby area. In a totally stubby area, the ABR (Area Border Router) suppresses the generation of certain types of LSAs (Link State Advertisements) to reduce the amount of routing information in the area. This helps in reducing the size of the routing table and reducing the processing overhead of routers.

The types of LSAs that are suppressed in a totally stubby area are:

  1. Type 3 Summary LSA: In OSPF, summary LSAs are used to advertise routes from one area to another area. In a totally stubby area, the ABR suppresses the generation of type 3 summary LSAs, which advertise routes from Area 2 to other areas. This is because in a totally stubby area, the only way to reach external destinations is through the default route generated by the ABR.

  2. Type 4 ASBR Summary LSA: In OSPF, ASBR (Autonomous System Boundary Router) summary LSAs are used to advertise routes from an ASBR to other areas. In a totally stubby area, the ABR suppresses the generation of type 4 ASBR summary LSAs, which advertise routes from an ASBR in Area 2 to other areas.

  3. Type 5 External LSA: In OSPF, external LSAs are used to advertise routes from outside the OSPF domain into the OSPF domain. In a totally stubby area, the ABR suppresses the generation of type 5 external LSAs, which advertise routes from external sources into Area 2.

  4. Type 2 Network LSA: In OSPF, network LSAs are used to advertise information about networks connected to a router. In a totally stubby area, the ABR suppresses the generation of type 2 network LSAs, which advertise information about networks connected to routers in Area 2.

Therefore, the LSAs that Router B suppresses from Area 2 are: Type 3 Summary LSA, Type 4 ASBR Summary LSA, Type 5 External LSA, and Type 2 Network LSA. It does not suppress the Type 1 Router LSA, which advertises information about the router itself.