Cisco IOS OSPF邻居关系不能正常建立的原因和解决方法

[align=center]Cisco IOS OSPF邻居关系不能正常建立的原因和解决方法[/align]
[align=left](1)接口上没有激活ospf
就是在network语句的时候没有匹配清楚，比如配置了错误的反掩码不对，在show ip ospf interface的时候不会显示你希望激活的接口
使用show ip ospf interface来验证
这时候的邻居表是空的
>R2#show ip ospf neighbor
R2#
(2)物理层或者是数据链路层协议down.使用show ip int brief 或者是 show int type nomber
会导致ospf packet 封装失败。
(3)建立邻居的接口被passive掉 [/align]

[align=left] R2#show ip ospf interface Ethernet 0 Ethernet0 is up, line protocol is up Internet Address 131.108.1.2/24, Area 0 Process ID 1, Router ID 131.108.1.2, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) 131.108.1.2, Interface address 131.108.1.2 No backup designated router on this network Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 No Hellos (Passive interface) Neighbor Count is 0, Adjacent neighbor count is 0 Suppress hello for 0 neighbor(s)[/align]

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(4)OSPF的hello组播地址被ACL Block [/align]

[align=left] R1# interface Ethernet0 ip address 131.108.1.1 255.255.255.0 ip access-group 100 in ! access-list 100 permit tcp any any access-list 100 permit udp any any access-list 101 permit ip 131.108.1.0 0.0.0.255 host 224.0.0.5 R2# interface Ethernet0 ip address 131.108.1.2 255.255.255.0 ip access-group 100 in ! access-list 100 permit tcp any any access-list 100 permit udp any any access-list 101 permit ip 131.108.1.0 0.0.0.255 host 224.0.0.5 R2#debug ip packet 101 detail IP packet debugging is on (detailed) for access list 101 IP: s=131.108.1.2 (Ethernet0), d=224.0.0.5, len 68, access denied, proto=89 这时候的邻居关系是INIT R2#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 131.108.2.1 1 INIT/- 00:00:33 131.108.1.1 Ethernet0 R1#show access-list 101 Extended IP access list 101 permit ip 131.108.1.0 0.0.0.3 host 224.0.0.5 (8 matches) R1#debug ip packet 101 detail IP packet debugging is on (detailed) for access list 101 R1# IP: s=131.108.1.1 (local), d=224.0.0.5 (Ethernet0), len 60, sending broad/multicast, proto =89 IP: s=131.108.1.2 (Ethernet0), d=224.0.0.5, len 82, access denied, proto=89 IP: s=131.108.1.1 (local), d=224.0.0.5 (Ethernet0), len 60, sending broad/multicast, proto =89 IP: s=131.108.1.2 (Ethernet0), d=224.0.0.5, len 82,access denied, proto=89[/align]

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(5)在broadcast链路上的子网掩码不匹配
(6)Hello/dead 间隔不匹配
(7)认证方式或者是认证密码不匹配
使用debug ip ospf adj 来查看,可以自己使用不同的情况来验证
(8)两台路由器处于不同的AREA [/align]

[align=left] R1#debug ip ospf adj OSPF adjacency events debugging is on R1# OSPF: Rcv pkt from 131.108.1.2, Ethernet0, area 0.0.0.0 mismatch area 0.0.0.1 in the header R2#show log %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link but not found from 131.108.1.1, Ethernet0[/align]

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(9)Stub/transit/NSSA 区域类型不匹配
这个是常常不小心会被忘记的。 [/align]

[align=left] R1#debug ip ospf adj OSPF adjacency events debugging is on R1# OSPF: Rcv hello from 131.108.0.1 area 1 from Ethernet0 131.108.1.2 OSPF: Hello from 131.108.1.2 with mismatched Stub/Transit area option bit R1#debug ip ospf adj OSPF adjacency events debugging is on R1# OSPF: Rcv hello from 131.108.0.1 area 1 from Ethernet0 131.108.1.2 OSPF: Hello from 131.108.1.2 with mismatched NSSA option bit[/align]

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(10)使用secondary IP来建立OSPF adjacency[/align]

[align=left]R2# interface FastEthernet0/0 ip address 131.108.1.2 255.255.255.0 secondary ip address 131.108.4.2 255.255.255.0 R1# interface Ethernet0 ip address 131.108.1.1 255.255.255.0 R2#debug ip ospf adj OSPF adjacency events debugging is on R2# OSPF: Rcv pkt from 131.108.1.1, FastEthernet0/0, area 0.0.0.1 : src not on the same network[/align]

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(11)OSPF网络类型不匹配（P-TO-P 和P-TO-M网络类型在hello时间间隔相同的情况下可以建立full关系，但是会缺少一条路由
可以做一下相关使用验证)
(12)NBMA (Frame Relay, X.25, SMDS, and so on)网络类型上没有手动指定neighbor ip 地址邻居一直都是ATTEMPT状态(13)在Router 两边的frame-relay map/dialer map语句声明中缺少了broadcast参数
(14)接口两边的MTU 不匹配
在cisco ios 12.0.3中加入了对mtu的检测，而低于这个版本的ios会忽略mtu检测，需要查看router 的ios version，debug ip ospf adj的结
果是发现有大量的dbd重传，出现loading的原因就是一边的router需要对mtu进行检测，而一边忽略。 [/align]

[align=left] R2#debug ip ospf adj OSPF adjacency events debugging is on R2# OSPF: Retransmitting request to 131.108.2.1 on Serial0 OSPF: Database request to 131.108.2.1 OSPF: sent LS REQ packet to 131.108.1.1, length 12 OSPF: Retransmitting request to 131.108.2.1 on Serial0 解决方法是接口命令：mtu 4470 而不是：ip mtu 4470 这时候的状态是 loading 。 R2#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 131.108.2.1 1 LOADING/- 00:00:37 131.108.1.1 Serial0 还有一种mtu不匹配的情况是邻居关系是EXSTART，因为两边的mtu都需要检测，而mtu大小又不匹配. R2#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 131.108.2.1 1 EXSTART/- 00:00:33 131.108.1.1 Serial0 R1#debug ip ospf adj OSPF: Retransmitting DBD to 131.108.1.2 on Serial0.1 OSPF: Send DBD to 131.108.1.2 on Serial0.1 seq 0x1E55 opt 0x2 flag 0x7 len 32 OSPF: Rcv DBD from 131.108.1.2 on Serial0.1 seq 0x22AB opt 0x2 flag 0x7 len 32 mtu 1500 state EXSTART OSPF: Nbr 131.108.1.2 has larger interface MTU[/align]

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(15)在broadcast网络上需要选举dr，而这时候两边的优先级又都是0
(16)在Asynchronous Interfaces上的OSPF邻居关系 [/align]

[align=left] R1# interface Async1 description ASYNC LINE TO R2 ip address 131.108.1.1 255.255.255.0 encapsulation ppp async mode dedicated dialer in-band dialer map ip 131.108.1.2 name Router2 broadcast dialer-group 1 ppp authentication chap R2# interface Async1 description ASYNC LINE TO R1 ip address 131.108.1.2 255.255.255.0 encapsulation ppp async mode dedicated dialer in-band dialer map ip 131.108.1.1 name Router2 broadcast dialer-group 1 ppp authentication chap 解决方法是在两个使用async default routing 或者asyn dynamic routing 接口命令[/align]

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(15)两个路由器的Router id相同，ospf的master和slave关系不能确定 [/align]

[align=left] R2#debug ip ospf adj OSPF: Retransmitting DBD to 131.108.2.1 on Serial0 OSPF: Send DBD to 131.108.2.1 on Serial0 seq 0x793 opt 0x2 flag 0x7 len 32 OSPF: Rcv DBD from 131.108.2.1 on Serial0 seq 0x25F7 opt 0x2 flag 0x7 len 32 mtu 0 state EXSTART OSPF: First DBD and we are not SLAVE[/align]

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(16)因为router接口的物理问题而导致的 ospf packet checksum错误，接着就重传的问题。 [/align]

[align=left] R2#show log %OSPF-4-ERRRCV: Received invalid packet: Bad Checksum from 131.108.1.1, Serial0 %OSPF-4-ERRRCV: Received invalid packet: Bad Checksum from 131.108.1.1, Serial0 R2#debug ip ospf adj OSPF adjacency events debugging is on R2# OSPF: Retransmitting request to 131.108.2.1 on Serial0 OSPF: Database request to 131.108.2.1 OSPF: sent LS REQ packet to 131.108.1.1, length 12 OSPF: Retransmitting request to 131.108.2.1 on Serial0[/align]