ospf邻居状态在Exstart与Exchange来回切换解决方法

设备现象：

路由器不断显示如下信息：

00:33:10: %OSPF-5-ADJCHG: Process 100, Nbr 88.10.10.254 on FastEthernet1/1 from EXCHANGE to FULL, Exchange Done
00:33:11: %OSPF-5-ADJCHG: Process 100, Nbr 88.10.10.254 on FastEthernet1/1 from EXCHANGE to FULL, Exchange Done
00:33:11: %OSPF-5-ADJCHG: Process 100, Nbr 88.10.10.254 on FastEthernet1/1 from EXCHANGE to FULL, Exchange Done
00:33:12: %OSPF-5-ADJCHG: Process 100, Nbr 88.10.10.254 on FastEthernet1/1 from EXCHANGE to FULL, Exchange Done
00:33:12: %OSPF-5-ADJCHG: Process 100, Nbr 88.10.10.254 on FastEthernet1/1 from EXCHANGE to FULL, Exchange Done
00:33:12: %OSPF-5-ADJCHG: Process 100, Nbr 88.10.10.254 on FastEthernet1/1 from EXCHANGE to FULL, Exchange Done

 

查看邻居状态：

cisco-master#sh ip ospf neighbor
Neighbor ID     Pri   State            Dead Time   Address         Interface
10.88.90.254      1   FULL/DR          00:00:30    10.88.90.254    FastEthernet0/0
10.88.90.112      1   Exstart/DROTHER  00:00:30    10.88.90.112    FastEthernet0/0
26.10.10.254      1   FULL/DR          00:00:30    172.0.0.1       FastEthernet0/1
69.10.10.254      1   FULL/DR          00:00:30    172.1.0.1       FastEthernet1/0
88.10.10.254      1   FULL/DR          00:00:33    172.2.0.1       FastEthernet1/1

cisco-master#sh ip ospf neighbor
Neighbor ID     Pri   State             Dead Time   Address         Interface
10.88.90.254      1   FULL/DR           00:00:30    10.88.90.254    FastEthernet0/0
10.88.90.112      1   Exchange/DROTHER  00:00:30    10.88.90.112    FastEthernet0/0
26.10.10.254      1   FULL/DR           00:00:30    172.0.0.1       FastEthernet0/1
69.10.10.254      1   FULL/DR           00:00:30    172.1.0.1       FastEthernet1/0
88.10.10.254      1   FULL/DR           00:00:33    172.2.0.1       FastEthernet1/1

邻居状态在Exstart与Exchange中来回切换。

两种解决方法：

参考此文解决：

由于两路由器间的MTU不匹配引起的，调整相应接品的MTU或者设置为忽略检测MTU，该设置不支持交换口。

在接口上启用如下命令来忽略MTU的检测：

cisco-master#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
cisco-master(config)#interface fastEthernet 0/0
cisco-master(config-if)#ip ospf mtu-ignore