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网络技术是从1990年代中期发展起来的新技术，它把互联网上分散的资源融为有机整体，实现资源的全面共享和有机协作，使人们能够透明地使用资源的整体能力并按需获取信息。资源包括高性能计算机、存储资源、数据资源、信息资源、知识资源、专家资源、大型数据库、网络、传感器等。 当前的互联网只限于信息共享，网络则被认为是互联网发展的第三阶段。 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
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
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
(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
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
(9)Stub/transit/NSSA 区域类型不匹配
这个是常常不小心会被忘记的。
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
网络的神奇作用吸引着越来越多的用户加入其中，正因如此，网络的承受能力也面临着越来越严峻的考验―从硬件上、软件上、所用标准上......，各项技术都需要适时应势，对应发展，这正是网络迅速走向进步的催化剂。
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