OSPF notes [dr and bdr]

DR: Specify router

BDR： Backup router

The election process ： It happened in 2-way After the state 【2-way yes ospf Of 5 One of the States , It is called two-way communication state . At this point, it can be seen that a neighbor relationship has been established with neighboring routes , At the same time, it is the basis of establishing adjacency relationship 】. At election DR The higher priority is DR, The second is BDR; If DR If the priority is the same Route-ID Big for DR. It should be noted that ：DR Not preemptive , That is, when a network is determined DR after , A new router is connected and its DR Priority must be high for all routers in the network 【 Normally DR The highest priority is DR Router 】, But this new router can't be DR, This is because the network already exists DR 了 , and BDR Is preemptive .

DR The role of ： Not DR/BDR The router of will send the updated link information to DR, Not in ospf Flooding in the network . This greatly reduces the link overhead .