配置OSPF的DR选择
如下图所示，R1的优先级为100，它是网络中最高的优先级，所以R1被选为DR，R3的优先级次高，被选为BDR；R2的优先级为0，不参加DR/BDR选举；R4优先级为默认值；
配置接口IP地址：
[r1]int g0/0/0
[r1-GigabitEthernet0/0/0]ip address 10.1.1.1 24
配置类似，不在阐述；
配置OSPF协议：
[r1]ospf 100 router-id 91.1.1.1
[r1-ospf-100]area 0
[r1-ospf-100-area-0.0.0.0]network 10.1.1.0 0.0.0.255
配置类似，不在阐述；
修改接口OSPF DR优先级：
[r1]int g0/0/0
[r1-GigabitEthernet0/0/0]ospf dr-priority ?
INTEGER<0-255> Router priority value
查看接口MA网络DR/BDR信息：
[r1]display ospf int g0/0/0
OSPF Process 100 with Router ID 91.1.1.1
Interfaces
Interface: 10.1.1.1 (GigabitEthernet0/0/0)
Cost: 1 State: DR Type: Broadcast MTU: 1500
Priority: 100
Designated Router: 10.1.1.1
Backup Designated Router: 10.1.1.3
Timers: Hello 10 , Dead 40 , Poll 120 , Retransmit 5 , Transmit Delay 1
[r3]display ospf int g0/0/0
OSPF Process 100 with Router ID 10.1.1.3
Interfaces
Interface: 10.1.1.3 (GigabitEthernet0/0/0)
Cost: 1 State: BDR Type: Broadcast MTU: 1500
Priority: 80
Designated Router: 10.1.1.1
Backup Designated Router: 10.1.1.3
Timers: Hello 10 , Dead 40 , Poll 120 , Retransmit 5 , Transmit Delay 1
