OSPF Router Suppressing LSAs in Totally Stubby Area
Question
R8 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 R8 suppress from
Area 2? (Choose three.)
Answers
Explanations
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In OSPF, there are several types of LSAs (Link State Advertisements) that are used to distribute routing information among the routers within the same area or between different areas. Each LSA type carries specific information about the network topology, such as router, network, and route information.
When an area is configured as a totally stubby area, it means that the area will not accept any external routes or summary routes, and instead, it will only accept routes that are directly connected within the area. In this scenario, R8 is an OSPF router connected to both Area 0 and Area 2, where Area 2 is configured as a totally stubby area.
As a result of this configuration, R8 will suppress the following three LSA types from Area 2:
Type 3 - Summary LSA: This LSA type carries information about the summary routes that are generated by an ABR (Area Border Router) between different areas. In a totally stubby area, R8 will not accept any summary routes, so it will suppress Type 3 LSAs.
Type 4 - ASBR Summary LSA: This LSA type carries information about the ASBR (Autonomous System Boundary Router) that redistributes external routes into OSPF. In a totally stubby area, R8 will not accept any external routes, so it will suppress Type 4 LSAs.
Type 5 - External LSA: This LSA type carries information about the external routes that are redistributed into OSPF by an ASBR. In a totally stubby area, R8 will not accept any external routes, so it will suppress Type 5 LSAs.
However, R8 will not suppress the following two LSA types from Area 2:
Type 1 - Router LSA: This LSA type carries information about the local router's interfaces and their associated metrics. It is used to build the SPF (Shortest Path First) tree within an area, regardless of whether it is a stubby or non-stubby area.
Type 2 - Network LSA: This LSA type carries information about multi-access networks and their associated routers. It is also used to build the SPF tree within an area, regardless of whether it is a stubby or non-stubby area.
