当在NBMA网络（如帧中继、ATM）中配置OSPF，必须注意哪个路由器是网络的DR和BDR，DR和BDR要求与网络中的所有路由器都有完全的逻辑连接。
同时，根据所使用的是四种网络类型中的哪一种（广播式、非广播式、点到点、点到多点），有必要使用额外的配置。
这个实验是在非广播的NBMA帧中继网络中使用了OSPF。这种类型是帧中继网络中物理接口的缺省类型。在非广播式网络中，存在一个DR或BDR，这要根据网络的性能，这要根据网络的性能，这个DR和BDR必须有一个包含所有处于帧中继的路由器的静态表，在OSPF进程中使用邻居命令可以完成这个任务。
对于这个实验，DR是路由器3，因为它具有与网络上其它所有路由器的完整的物理连接。如上图表示。
// 帧交换机
frame-relay switching
int s2/0
encapsulation frame-relay
clock rate 64000
frame-relay intf-type dce
frame-relay route 200 int s3/0 300
int s3/0
encapsulation frame-relay
clock rate 64000
frame-relay intf-type dce
frame-relay route 300 int s2/0 200
frame-relay route 399 int s4/0 400
int s4/0
encapsulation frame-relay
clock rate 64000
frame-relay intf-type dce
frame-relay route 400 int s2/0 399
// R2 //
int lo0
ip ad 2.2.2.2 255.255.255.0
int s2/0
encapsulation frame-relay
ip ospf priority 0 //优先级为0，不参与DR选举
ip ad 192.1.1.2 255.255.255.0
frame-relay map ip 192.1.1.3 200 broadcast
frame-relay map ip 192.1.1.4 200 broadcast
router os 1
network 2.2.2.2 0.0.0.0 area 0
network 192.1.1.2 0.0.0.0 area 0
// R3 //
int lo0
ip ad 3.3.3.3 255.255.255.0
int s3/0
encapsulation frame-relay
ip address 192.1.1.3 255.255.255.0
frame-relay map ip 192.1.1.2 300 broadcast
frame-relay map ip 192.1.1.4 399 broadcast
router os 1
network 3.3.3.3 0.0.0.0 area 0
network 192.1.1.3 0.0.0.0 area 0
neighbor 192.1.1.2 //NBMA模式下OSPF必须手动指定邻居
neighbor 192.1.1.4 //NBMA模式下OSPF必须手动指定邻居
// R4 //
int lo0
ip ad 4.4.4.4 255.255.255.0
int s4/0
encapsulation frame-relay
ip ad 192.1.1.4 255.255.255.0
ip ospf priority 0 //优先级为0，不参与DR选举
frame-relay map ip 192.1.1.2 400 broadcast
frame-relay map ip 192.1.1.3 400 broadcast
router os 1
network 4.4.4.4 0.0.0.0 area 0
network 192.1.1.4 0.0.0.0 area 0
验证过程：
一、首先来检查DR选举是否按我们的设计，R3被选举为DR，R2、R4不参与选举，同时注意网络类型是否为NBMA，hello时间间隔是否为30秒。。。。。。
r3#sh ip os int s3/0
Serial3/0 is up, line protocol is up
Internet Address 192.1.1.3/24, Area 0
Process ID 1, Router ID 3.3.3.3, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 3.3.3.3, Interface address 192.1.1.3
No backup designated router on this network
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
Hello due in 00:00:27
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 2, maximum is 2
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 2, Adjacent neighbor count is 2
Adjacent with neighbor 4.4.4.4
Adjacent with neighbor 2.2.2.2
Suppress hello for 0 neighbor(s)
r2#sh ip os int s2/0
Serial2/0 is up, line protocol is up
Internet Address 192.1.1.2/24, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DROTHER, Priority 0
Designated Router (ID) 3.3.3.3, Interface address 192.1.1.3
No backup designated router on this network
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
Hello due in 00:00:20
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 3.3.3.3 (Designated Router)
Suppress hello for 0 neighbor(s)
r4#sh ip ospf int s4/0
Serial4/0 is up, line protocol is up
Internet Address 192.1.1.4/24, Area 0
Process ID 1, Router ID 4.4.4.4, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DROTHER, Priority 0
Designated Router (ID) 3.3.3.3, Interface address 192.1.1.3
No backup designated router on this network
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
Hello due in 00:00:05
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 3.3.3.3 (Designated Router)
Suppress hello for 0 neighbor(s)
二、接下来观察各路由器邻居建立情况：
r2#sh ip os nei
Neighbor ID Pri State Dead Time Address Interface
3.3.3.3 1 FULL/DR 00:01:50 192.1.1.3 Serial2/0
r3#sh ip os nei
Neighbor ID Pri State Dead Time Address Interface
4.4.4.4 0 FULL/DROTHER 00:01:41 192.1.1.4 Serial3/0
2.2.2.2 0 FULL/DROTHER 00:01:30 192.1.1.2 Serial3/0
r3#sh ip os nei
Neighbor ID Pri State Dead Time Address Interface
3.3.3.3 1 FULL/DR 00:01:48 192.1.1.3 Serial4/0
三、最后验证路由：
r2#sh ip ro
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/65] via 192.1.1.3, 00:00:17, Serial2/0
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/65] via 192.1.1.4, 00:00:17, Serial2/0
C 192.1.1.0/24 is directly connected, Serial2/0
r3#sh ip ro
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 192.1.1.2, 00:00:38, Serial3/0
3.0.0.0/24 is subnetted, 1 subnets
C 3.3.3.0 is directly connected, Loopback0
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/65] via 192.1.1.4, 00:00:38, Serial3/0
C 192.1.1.0/24 is directly connected, Serial3/0
r4#sh ip ro
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 192.1.1.2, 00:01:04, Serial4/0
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/65] via 192.1.1.3, 00:01:04, Serial4/0
4.0.0.0/24 is subnetted, 1 subnets
C 4.4.4.0 is directly connected, Loopback0
C 192.1.1.0/24 is directly connected, Serial4/0
转载自：http://blog.sina.com.cn/s/blog_56fdccdb010007ib.html
