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

　　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)

　　(4)OSPF的hello组播地址被ACL Block

　　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