Which three functions are performed by an OSPF area border router (ABR)? (Choose three)
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A. B. C. D. E.ABD
An OSPF (Open Shortest Path First) Area Border Router (ABR) is a router that connects two or more OSPF areas together. The ABR performs several essential functions that are necessary for the proper functioning of the OSPF network. The three functions that an OSPF ABR performs are as follows:
Flooding Summary LSAs to Connected Areas: When an OSPF ABR connects to two or more OSPF areas, it receives Summary LSAs (Link State Advertisements) from all of the areas. These Summary LSAs contain information about the routes that are available in each area. The ABR is responsible for flooding these Summary LSAs to all of the other connected areas. This ensures that all routers in the OSPF network have complete information about the routes that are available throughout the network.
Flooding ASBR Summary LSAs to Connected Areas: An Autonomous System Boundary Router (ASBR) is a router that connects to an external routing domain or network. When an OSPF ABR connects to an ASBR, it receives ASBR Summary LSAs. These LSAs contain information about the external routes that are available through the ASBR. The ABR is responsible for flooding these ASBR Summary LSAs to all of the other connected areas. This ensures that all routers in the OSPF network have complete information about the external routes that are available through the ASBR.
Performing Summarization on Routes Headed to Area 0: OSPF uses a hierarchical network design in which the network is divided into multiple areas. The backbone area, also known as Area 0, is the central area of the network, and all other areas connect to it. When an OSPF router sends a packet to a destination that is located in Area 0, it must send the packet through an ABR. The ABR is responsible for summarizing the routes that are headed to Area 0. This ensures that the routing tables in the OSPF network are not overloaded with unnecessary information, which can cause routing problems and network congestion.
In summary, the three functions performed by an OSPF ABR are flooding Summary LSAs and ASBR Summary LSAs to connected areas, and performing summarization on routes headed to Area 0.