OSPF为什么同一个区域内会有多个DR/BDR

1. OSPF 的DR/BDR是在同一个MA网络（如以太网）中进行选举，并非在一个区域内全部路由器进行选举

按上面的拓扑图为例子：

在R8上面查看OSPF有两个DR/BDR

R8#show ip os
R8#show ip ospf ne
R8#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
7.7.7.7 1 FULL/DR 00:00:32 120.0.0.7 FastEthernet0/1
10.10.10.10 1 FULL/BDR 00:00:32 120.0.0.10 FastEthernet0/1
6.6.6.6 1 FULL/DR 00:00:35 110.0.0.6 FastEthernet0/0
9.9.9.9 1 FULL/BDR 00:00:32 110.0.0.9 FastEthernet0/0

R6上面查看OSPF有两个DR/BDR：

R6#show ip os
R6#show ip ospf ne

Neighbor ID Pri State Dead Time Address Interface
8.8.8.8 1 FULL/DROTHER 00:00:37 110.0.0.8 FastEthernet0/0
9.9.9.9 1 FULL/BDR 00:00:32 110.0.0.9 FastEthernet0/0

R9#show ip os
R9#show ip ospf ne

Neighbor ID Pri State Dead Time Address Interface
6.6.6.6 1 FULL/DR 00:00:37 110.0.0.6 FastEthernet0/0
8.8.8.8 1 FULL/DROTHER 00:00:39 110.0.0.8 FastEthernet0/0

R7#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
8.8.8.8 1 FULL/DROTHER 00:00:32 120.0.0.8 FastEthernet0/1
10.10.10.10 1 FULL/BDR 00:00:35 120.0.0.10 FastEthernet0/1

R10#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
7.7.7.7 1 FULL/DR 00:00:37 120.0.0.7 FastEthernet0/1
8.8.8.8 1 FULL/DROTHER 00:00:34 120.0.0.8 FastEthernet0/1