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cisco braindumps free.OSPF routers use link state announcements (LSAs ) to communicate with each other. One type of LSA is the Hello message, which is used to establish adjacencies as well as to implement the survive function port Hello messages are generated at an interval of 10 seconds, and when sharing link information (directly connected routes), the link information is sent to the DR ( 224.0.0.6), which in turn propagates it to each OSPF route S (224.0.0.5) on the network segment In the point-to-point linkOn the DR/BDR, no DR/BDR is used,so the destination address of all OSPF packets is 224.0.0.5o Figure 19.2 DR and BDRBDR election processID= 10.37.82.1 preferred ID = 10.37.83.37 preferred ID = 10.37.82.40 preferredThe OSPF router with the highest priority in the segment will become the DR.If the priority is the same, the router with the highest router ID will becomepriority =1 priority =1 priority =1 priority =1By default, all routers have a priority of 1 (priority is an 8-bit value that takes the range 0-255 ). o If the DR fails, the BDR will be promoted to DR, and another router will be elected to BDR. o Figure 19.2 shows an election example where router E is elected to DR and router B is elected to BDR. o In this example, notice that all In this example, notice that all routers have a default priority of 1, so router E is elected as DR because its router ID is the largest, and router B is elected as BDR because its router ID is the second largest. If a router has a priority of 0, it will never be a DR or BDROID =10.37.81.25 preferred ID =10.37.83.39 precedence =1 priority =1The priority used to elect DRs and BDRs is configured on the interface using the interface subconfiguration mode command ip ospf priorityDRof the interface. After being elected as DR and BDR, routers will always play this role even if a router with a higher priority has established an adjacency with them: an election or re-election will occur only when there is no DR or BDR.