What is the purpose of the designated router in OSPF?
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A. B. C. D.D
It is the designated router's job to form an adjacency with all other OSPF routers on the link and to advertise the link-state information to the AS.
The correct answer is D. The purpose of the designated router (DR) in OSPF (Open Shortest Path First) is to form adjacencies with other OSPF routers in a broadcast domain. OSPF is a link-state routing protocol that is used to dynamically calculate the shortest path between two points on a network. In a broadcast domain, multiple OSPF routers may be connected to the same segment, and each router may form adjacencies with all other routers on that segment. However, forming adjacencies with every other router on a segment can be resource-intensive, especially on larger networks with many routers.
To reduce the amount of overhead associated with forming adjacencies, OSPF elects one router on the segment to be the designated router (DR), and another router to be the backup designated router (BDR). These two routers are responsible for forming adjacencies with all other OSPF routers on the segment, and then propagating topology information to the other routers. This reduces the amount of overhead required to maintain adjacencies, and ensures that all routers have the same view of the network topology.
When a new router is added to the broadcast domain, it sends a hello packet to the multicast address 224.0.0.5. The DR and BDR respond to the hello packet and form adjacencies with the new router. The DR and BDR then inform the new router about the network topology, including the OSPF router IDs and the link-state database. The new router then becomes fully integrated into the OSPF network.
It's worth noting that the designated router is not needed in all OSPF environments. In point-to-point and point-to-multipoint networks, there is no need to elect a designated router because there are only two routers or one central router, respectively. Additionally, in OSPF stub and totally stub areas, the designated router is not used because the area is disconnected from the rest of the network and does not require the overhead associated with the DR/BDR election process.