一、配置要求
1.路由器名为cisco1,cisco2和cisco3;
2.配置IP地址如图所示，cisco1的环回口IP地址为1.1.1.1，255.255.255.0，cisco3为3.3.3.3，子网掩码为255.255.255.0。
3.三台路由器属于同一个OSPF区域0；
4.将三台路由器相连，并在路由器上启用OSPF路由协议；
5.用扩展PING命令，测试用1.1.1.1 到3.3.3.3 的连通性
二、拓扑
三、步骤
1.设置路由选择协议
cisco1(config)#router ospf 1
cisco1(config-router)#network 192.168.12.0 0.0.0.255 area 0
cisco1(config-router)#network 1.1.1.1 0.0.0.0 area 0
注：利用反掩码技术来匹配某一接口，如果匹配到了，那么就把这个接口的网段参与到OSPF的进程中
cisco2(config)#router ospf 1
cisco2(config-router)#network 192.168.0.0 0.0.255.255 area 0
注：虽然只写入了一个条目，但是它匹配到了192.168.12.2和192.168.23.2这两个接口，所以他们都会参与到OSPF进程中
cisco3(config)#router ospf 1
cisco3(config-router)#network 3.3.3.0 0.0.0.255 area 0
cisco3(config-router)#network 192.168.23.0 0.0.0.255 area 0
2.查看路由表
cisco1#show ip route
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/75] via 192.168.12.2, 00:00:59, Ethernet0
C 192.168.12.0/24 is directly connected, Ethernet0
O 192.168.23.0/24 [110/74] via 192.168.12.2, 00:00:59, Ethernet0
注：OSPF的代号为O。管理距离值为110。度量值的计算方法是cost=10的8次方除以带宽。
观察OSPF邻居关系的建立情况
cisco1#debug ip ospf adj
cisco1(config)#int e0
cisco1(config-if)#shutdown
cisco1(config-if)#
注：开启OSPF建立邻居关系的debug信息。关闭端口！以验证邻居建立情况
02:00:59: %LINK-5-CHANGED: Interface Ethernet0, changed state to administratively down----等待接口被管理员性关闭后，再用no shutdown打开
02:01:00: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet0, changed state to down
cisco1(config-if)#no shutdown----打开端口
cisco1(config-if)#
02:01:05: OSPF: Interface Ethernet0 going Up
02:01:05: OSPF: Build router LSA for area 0, router ID 1.1.1.1, seq 0x80000005
02:01:07: %LINK-3-UPDOWN: Interface Ethernet0, changed state to up
02:01:08: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet0, changed state to up
02:01:12: OSPF: 2 Way Communication to 192.168.23.2 on Ethernet0, state 2WAY
02:01:12: OSPF: Backup seen Event before WAIT timer on Ethernet0
02:01:12: OSPF: DR/BDR election on Ethernet0
02:01:12: OSPF: Elect BDR 1.1.1.1
02:01:12: OSPF: Elect DR 192.168.23.2
02:01:12: OSPF: Elect BDR 1.1.1.1
02:01:12: OSPF: Elect DR 192.168.23.2
02:01:12: DR: 192.168.23.2 (Id) BDR: 1.1.1.1 (Id)
02:01:12: OSPF: Send DBD to 192.168.23.2 on Ethernet0 seq 0x1513 opt 0x42 flag 0x7 len 32
02:01:15: OSPF: Rcv DBD from 192.168.23.2 on Ethernet0 seq 0x169C opt 0x42 flag 0x7 len 32 mtu 1500 state EXSTART
02:01:15: OSPF: NBR Negotiation Done. We are the SLAVE
02:01:15: OSPF: Send DBD to 192.168.23.2 on Ethernet0 seq 0x169C opt 0x42 flag 0x2 len 112
02:01:15: OSPF: Rcv DBD from 192.168.23.2 on Ethernet0 seq 0x169D opt 0x42 flag 0x3 len 92 mtu 1500 state EXCHANGE
02:01:15: OSPF: Send DBD to 192.168.23.2 on Ethernet0 seq 0x169D opt 0x42 flag 0x0 len 32
02:01:15: OSPF: Database request to 192.168.23.2
02:01:15: OSPF: sent LS REQ packet to 192.168.12.2, length 12
02:01:15: OSPF: Rcv DBD from 192.168.23.2 on Ethernet0 seq 0x169E opt 0x42 flag 0x1 len 32 mtu 1500 state EXCHANGE
02:01:15: OSPF: Exchange Done with 192.168.23.2 on Ethernet0
02:01:15: OSPF: Send DBD to 192.168.23.2 on Ethernet0 seq 0x169E opt 0x42 flag 0x0 len 32
02:01:15: OSPF: Synchronized with 192.168.23.2 on Ethernet0, state FULL
02:01:15: %OSPF-5-ADJCHG: Process 1, Nbr 192.168.23.2 on Ethernet0 from LOADING to FULL, Loading Done
02:01:15: OSPF: Build router LSA for area 0, router ID 1.1.1.1, seq 0x80000006
cisco1(config-if)#end
cisco1#u all
问题分析：OSPF的整个邻居关系应该经历以下完整的过程
DOWN---INIT---2 WAY---EXSTART---EXCHANGE---LOADING---FULL
3.查看ospf邻居表
cisco1#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
192.168.23.2 1 FULL/DR 00:00:39 192.168.12.2 Ethernet0
注：OSPF的HELLO 时间为10秒，HOLD时间为40秒。可以显示对端邻居的接口IP地址，可以查看OSPF的邻居状态，稳定时为FULL。
cisco2#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/BDR 00:00:31 192.168.12.1 Ethernet0
3.3.3.3 1 FULL/ - 00:00:38 192.168.23.3 Serial1
注：-代表了cisco2和cisco3上却没有DR和BDR的选举
问题分析：为什么在cisco1和cisco2上有DR和BDR的选举过程，而cisco2和cisco3上却没有？我们要了解，对于DR和BDR的选举，是有条件的，那就是必须是要在多路访问的链路上进行，cisco1和cisco2是用以太网线链接，以太网的链路是星型结构，属于多路访问类型，可以参与DR和BDR的选举，但是cisco2和cisco3上使用的是serial线缆，它是属于点到点的专线结构，所以是没有必要参与DR和BDR的选举的。
4.查看参与OSPF进程的以太网口状态
cisco1#show ip ospf interface ethernet 0
Ethernet0 is up, line protocol is up
Internet Address 192.168.12.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10--------------------以太网类型为多路访问（brocast）
Transmit Delay is 1 sec, State DROTHER, Priority 0
Designated Router (ID) 192.168.23.2, Interface address 192.168.12.2
No backup designated router on this network
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:07
Index 1/1, 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 8 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 192.168.23.2 (Designated Router)
Suppress hello for 0 neighbor(s)
cisco2#show ip ospf interface serial 1
Serial1 is up, line protocol is up
Internet Address 192.168.23.2/24, Area 0
Process ID 1, Router ID 192.168.23.2, Network Type POINT_TO_POINT, Cost: 64--------------------Serial线缆为点到点类型的
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:00
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 2
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
Suppress hello for 0 neighbor(s)
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