What are two interarea OSPF LSA types? (Choose two.)

The correct answer is A. Type-4 ASBR summary LSAs B. Type 3 summary LSAs. A: The fourth LSA type, network example: In this example we have R1 that is redistributing information from the RIP router into OSPF. This makes R1 an ASBR (Autonomous System Border Router). What happens is that R1 will flip a bit in the router LSA to identify itself as an…

OSPF

Question

Exhibit

Options

AType-4 ASBR summary LSAs
BType 3 summary LSAs
CType 1 router LSAs
DType 2 network LSAs

How the community answered

(15 responses)

A
73% (11)
C
7% (1)
D
20% (3)

Explanation

A: The fourth LSA type, network example: In this example we have R1 that is redistributing information from the RIP router into OSPF. This makes R1 an ASBR (Autonomous System Border Router). What happens is that R1 will flip a bit in the router LSA to identify itself as an ASBR. When R2 who is an ABR receives this router LSA it will create a type 4 summary ASBR LSA and flood it into area 0. This LSA will also be flooded in all other areas and is required so all OSPF routers know where to find the ASBR. Router 2 can create a Type 3 summary LSA and flood it into area 0. This LSA will flood into all the other areas of our OSPF network. This way all the routers in other areas will know about the prefixes from other areas. Note: The name "summary" LSA is very misleading. By default OSPF is not going to summarize anything for you. There is however a command that let you summarize inter-area routes. Take a look at my OSPF summarization tutorial if you are interested. If you are looking at the routing table of an OSPF router and see some O IA entries you are looking at LSA type 3 summary LSAs. Those are your inter-area prefixes!

Topics

#OSPF LSA types#Type-3 summary LSA#Type-4 ASBR summary#interarea

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