实验拓扑：

实验需求：引入内部路由，运行多个OSPF进程，建立虚链路；所有路由器之间都能够相互ping通。
实验步骤：
配置路由器的每个端口的IP地址
R1:
enable
conf t
int f0/0
no shu
ip add 192.168.12.1 255.255.255.0
exit
int l 0
ip add 10.10.1.1 255.255.255.0
exit

R2:
enable
conf t
int f0/1
no shu
ip add 192.168.12.2 255.255.255.0
exit
int l 0
ip add 10.10.2.2 255.255.255.0
exit
int f0/0
no shu
ip add 192.168.23.2 255.255.255.0
exit

R3：
enable
conf t
int f 0/1
no shu
ip add 192.168.23.3 255.255.255.0
exit
int l 0
ip add 10.10.3.3 255.255.255.0
int f 0/0
no shu
ip add 192.168.34.3 255.255.255.0
exit

R4:
enable
conf t
int f0/1
no shu
ip add 192.168.34.4 255.255.255.0
exit
int l 0
ip add 10.10.4.4 255.255.255.0
exit
int f0/0
no shu
ip add 192.168.45.4 255.255.255.0
exit

R5:
enable
conf t
int f0/1
no shu
ip add 192.168.45.5 255.255.255.0
exit
int l 0
ip add 10.10.5.5 255.255.255.0
exit

在每个路由器开启OSPF并配置OSPF路由

R1:
router os 1
router-id 1.1.1.1
net 192.168.12.0 0.0.0.255 ar 0
net 10.10.1.0 0.0.0.255 ar 0
exit

R2:
router os 1
router-id 2.2.2.2
net 192.168.12.0 0.0.0.255 ar 0
net 10.10.2.0 0.0.0.255 ar 0
net 192.168.23.0 0.0.0.255 ar 0
exit

R3:
router os 1
router-id 3.3.3.3
net 192.168.23.0 0.0.0.255 ar 0
exit
router os 1
router-id 3.3.3.3
net 192.168.34.0 0.0.0.255 ar 12
net 10.10.3.0 0.0.0.255 ar 12
exit

R4:
router os 1
router-id 4.4.4.4
net 192.168.34.0 0.0.0.255 ar 12
net 192.168.45.0 0.0.0.255 ar 45
net 10.10.4.0 0.0.0.255 ar 45
exit

R5:
router os 45
router-id 5.5.5.5
net 192.168.45.0 0.0.0.255 ar 45
net 10.10.5.0 0.0.0.255 ar 45
exit

引入内部路由，做虚链路在R3与R4上作

R3：
router os 1
area 12 virtual-link 4.4.4.4
exit

R4:
router os 1
area 12 virtual-link 3.3.3.3
exit