1、形成邻居条件：
1）区域ID相同；
2）hello，dead时间一致；
3）认证，认证密码一致；
4）区域性质一致（例都是普通区域，或者都是末节区域等等）。
2、验证
2.1、基本配置
R1:
en
conf t
no ip domain-lookup
host R1
inter s1/1
ip add 10.10.1.1 255.255.255.252
description to-R2-s1/0
no shut
exit
interface Loopback100
ip address 1.1.1.1 255.255.255.0
router ospf 100
network 10.10.1.1 0.0.0.0 area 0
R2:
en
conf t
no ip domain-lookup
host R2
inter s1/0
ip add 10.10.1.2 255.255.255.252
description to-R1-s1/1
no shut
inter s1/1
ip add 10.10.2.1 255.255.255.252
description to-R3-s1/0
no shut
exit
interface Loopback200
ip address 2.2.2.2 255.255.255.0
router ospf 200
network 10.10.1.2 0.0.0.0 area 0
//此邻居关系理论上已经建立成功：
R1#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 0 FULL/ - 00:00:39 10.10.1.2 Serial1/1
R2#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 0 FULL/ - 00:00:31 10.10.1.1 Serial1/0
2.2、验证过程
2.2.1、区域不同
把R2的区域修改成area 1
R2(config-router)#network 10.10.1.2 0.0.0.0 area 1
R2(config-router)#
*Oct 23 15:53:50.927: %OSPF-5-ADJCHG: Process 200, Nbr 1.1.1.1 on Serial1/0 from FULL to DOWN, Neighbor Down: Interface down or detached
*Oct 23 15:53:50.935: %OSPF-6-AREACHG: 10.10.1.2/32 changed from area 0 to area 1
*Oct 23 15:53:57.755: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link but not found from 10.10.1.1, Serial1/0
//更改区域后，提示邻居关系已经中断，原因是区域号不一致，建议通过虚拟链路来实现。
R2(config-router)#do sh ip ospf nei
R2(config-router)#
//查看R2邻居已经丢失。
R1#sh ip ospf neighbor
R1#sh ip ospf neighbor
//查看R1邻居也已经丢失。
R2(config-router)#network 10.10.1.2 0.0.0.0 area 0
R2(config-router)#
*Oct 23 15:58:03.699: %OSPF-6-AREACHG: 10.10.1.2/32 changed from area 1 to area 0
*Oct 23 15:58:03.759: %OSPF-5-ADJCHG: Process 200, Nbr 1.1.1.1 on Serial1/0 from LOADING to FULL, Loading Done
R2(config-router)#do sh ip ospf nei
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 0 FULL/ - 00:00:33 10.10.1.1 Serial1/0
R2(config-router)#
//R2配置还原成area 0，邻居关系马上恢复。
R1#
*Oct 23 15:58:04.019: %OSPF-5-ADJCHG: Process 100, Nbr 2.2.2.2 on Serial1/1 from LOADING to FULL, Loading Done
//R1邻居关系也恢复。
2.2.2 hello，dead时间一致；
注：基于接口来修改时间，修改hello时，dead时间同时修改，保持为hello的4倍。
默认的时间如下：
R2(config-if)#do sh ip ospf inter s1/0
Serial1/0 is up, line protocol is up
Internet Address 10.10.1.2/30, Area 0
Process ID 200, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:05
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 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
修改如下：
R2(config-if)#ip ospf hello-interval 20
//由10s修改20s
R2(config-if)#do sh ip ospf inter s1/0
Serial1/0 is up, line protocol is up
Internet Address 10.10.1.2/30, Area 0
Process ID 200, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 20, Dead 80, Wait 80, Retransmit 5
oob-resync timeout 80
Hello due in 00:00:18
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 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
//已修改成为20s，同时dead时间也修改成80s
R2(config-if)#
R2(config-if)#
*Oct 23 16:05:07.747: %OSPF-5-ADJCHG: Process 200, Nbr 1.1.1.1 on Serial1/0 from FULL to DOWN, Neighbor Down: Dead timer expired
//提示邻居关系已中断，原因是dead时间不匹配。
还原配置：
R2(config-if)#no ip ospf hello-interval 20
R2(config-if)#do sh ip ospf inter s1/0
Serial1/0 is up, line protocol is up
Internet Address 10.10.1.2/30, Area 0
Process ID 200, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
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 0 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
R2(config-if)#
*Oct 23 16:07:27.843: %OSPF-5-ADJCHG: Process 200, Nbr 1.1.1.1 on Serial1/0 from LOADING to FULL, Loading Done
//邻居关系恢复。
单独修改dead时间：
R2(config-if)#ip ospf dead-interval 50
R2(config-if)#do sh ip ospf inter s1/0
Serial1/0 is up, line protocol is up
Internet Address 10.10.1.2/30, Area 0
Process ID 200, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 50, Wait 50, Retransmit 5
oob-resync timeout 50
Hello due in 00:00:00
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 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 1.1.1.1
Suppress hello for 0 neighbor(s)
//只修改dead时间，hello时间不变
R2(config-if)#
*Oct 23 16:09:27.739: %OSPF-5-ADJCHG: Process 200, Nbr 1.1.1.1 on Serial1/0 from FULL to DOWN, Neighbor Down: Dead timer expired
//邻居关系也会中断，提示与hello时间不同的现象一样。
R2(config-if)#no ip ospf dead-interval 50
*Oct 23 16:10:29.531: %OSPF-5-ADJCHG: Process 200, Nbr 1.1.1.1 on Serial1/0 from LOADING to FULL, Loading Done
//再还原配置。
2.2.3 认证，认证密码一致；
1）3认证类型
无认证；
明文认证；
MD5认证；
2）必要条件
认证类型和密码都要一致。
3）各种情况验证
第一种：两端无认证，默认的配置就符合这种情况，故不在此做验证。
第二种：两端都为明文认证，此情况不需要在此做验证，真有疑问，请找cisco研发；
第三种：两端都为MD5认证，同上；
第四种：无认证+明文认证；
R1：配置不改
R2：改为明文认证
R2(config-if)#ip ospf authentication
R2(config-if)#ip ospf authentication-key cisco
R2(config-if)#
*Oct 23 16:24:07.747: %OSPF-5-ADJCHG: Process 200, Nbr 1.1.1.1 on Serial1/0 from FULL to DOWN, Neighbor Down: Dead timer expired
R2(config-if)#
//配置完成后，提示邻居已经中断；
在R1上开启debug后输出信息如下：
R1#debug ip ospf events
OSPF events debugging is on
R1#
*Oct 23 16:24:47.983: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 10.10.1.1
*Oct 23 16:24:49.675: OSPF: Rcv pkt from 10.10.1.2, Serial1/1 : Mismatch Authentication type. Input packet specified type 1, we use type 0
//提示对方使用type 1（明文认证），我(R1)使用type 0（无认证）
第五种：无认证+MD5认证；
R1：配置不改
R2：改为MD5认证
R2(config-if)#ip ospf authentication message-digest
R2(config-if)#ip ospf authentication-key cisco
//邻居关系自然也是不能建立的。
查看R1的debug信息如下：
Oct 23 16:30:07.987: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/1 from 10.10.1.1
*Oct 23 16:30:09.639: OSPF: Rcv pkt from 10.10.1.2, Serial1/1 : Mismatch Authentication type. Input packet specified type 2, we use type 0
//提示对方使用type 2（MD5认证），我(R1)使用type 0（无认证）
第六种：明文认证+MD5认证+key相同；
R2保持上面配置，
R1改为明文认证：
R1(config-if)#ip ospf authentication-ke
R1(config-if)#ip ospf authentication-key cisco
在R2上开启debug信息如下：
*Oct 23 16:34:49.411: OSPF: Send with youngest Key 0
*Oct 23 16:34:49.411: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/0 from 10.10.1.2
*Oct 23 16:34:57.763: OSPF: Rcv pkt from 10.10.1.1, Serial1/0 : Mismatch Authentication type. Input packet specified type 1, we use type 2
//提示认证类型不同。
还原认证配置。
2.2.4、区域性质一致
有点累了，所以省略，有时间再做了------------