OSPF虚链路（virtual-link）配置实例 + 详细验证过程
这个配置将验证一个OSPF虚电路（Virtual-Link）的过程，重点在观察虚链路连接的临时网络与正常区域间路由有何区别。上图中区域4（area 4）没有和area 0直接相连。在R2与R3之间配置了一条虚链路。
// R1 //
int lo0
ip ad 1.1.1.1 255.255.255.0
int e0
ip ad 192.1.1.1 255.255.255.0
router os 1
network 192.1.1.0 0.0.0.255 area 0
// R2 //
int lo0
ip ad 2.2.2.2 255.255.255.0
int e0
ip ad 192.1.1.2 255.255.255.0
int e1
ip ad 193.1.1.2 255.255.255.0
router os 1
network 192.1.1.0 0.0.0.255 area 0
network 193.1.1.0 0.0.0.255 area 1
// R3 //
int lo0
ip ad 3.3.3.3 255.255.255.0
int e1
ip ad 193.1.1.3 255.255.255.0
int e0
ip ad 194.1.1.3 255.255.255.0
router os 1
network 193.1.1.0 0.0.0.255 area 1
network 194.1.1.0 0.0.0.255 area 4
// R4 //
int lo0
ip ad 4.4.4.4 255.255.255.0
int e0
ip ad 194.1.1.4 255.255.255.0
router os 1
network 194.1.1.0 0.0.0.255 area 4
基本配置完成后，我们在每台路由器上分别来验证一下：
r1#sh ip os nei
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 1 FULL/BDR 00:00:33 192.1.1.2 Ethernet0/0
r1#
r1#sh ip ro
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
O IA 193.1.1.0/24 [110/20] via 192.1.1.2, 00:00:19, Ethernet0/0
C 192.1.1.0/24 is directly connected, Ethernet0/0
//注意R1上有关于193.1.1.0的路由条目，是属于IA类型（域间路由）
r2#sh ip os nei
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/DR 00:00:35 192.1.1.1 Ethernet0/0
3.3.3.3 1 FULL/BDR 00:00:35 193.1.1.3 Ethernet1/0
r2#
r2#
r2#sh ip ro
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
C 193.1.1.0/24 is directly connected, Ethernet1/0
C 192.1.1.0/24 is directly connected, Ethernet0/0
r3#sh ip os nei
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 1 FULL/DR 00:00:32 193.1.1.2 Ethernet1/0
4.4.4.4 1 FULL/DR 00:00:34 194.1.1.4 Ethernet0/0
r3#sh ip ro
3.0.0.0/24 is subnetted, 1 subnets
C 3.3.3.0 is directly connected, Loopback0
C 193.1.1.0/24 is directly connected, Ethernet1/0
O IA 192.1.1.0/24 [110/20] via 193.1.1.2, 00:02:49, Ethernet1/0
C 194.1.1.0/24 is directly connected, Ethernet0/0
//注意R3中有关于192.1.1.0的路由是属于IA类型（域间路由）
r4#sh ip os nei
Neighbor ID Pri State Dead Time Address Interface
3.3.3.3 1 FULL/BDR 00:00:33 194.1.1.3 Ethernet0/0
r4#sh ip ro
4.0.0.0/24 is subnetted, 1 subnets
C 4.4.4.0 is directly connected, Loopback0
C 194.1.1.0/24 is directly connected, Ethernet0/0
//R4上没有关于AREA 0内的任何路由信息
我们下面在R2、R3上添加Virtual-link的配置：
R2：
router os 1
area 1 virtual-link 3.3.3.3
R3:
router os 1
area1 virtual-link 2.2.2.2
对比之前的路由信息，看有何区别：
r1#sh ip ro
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
O IA 193.1.1.0/24 [110/20] via 192.1.1.2, 00:00:01, Ethernet0/0
C 192.1.1.0/24 is directly connected, Ethernet0/0
O IA 194.1.1.0/24 [110/30] via 192.1.1.2, 00:00:01, Ethernet0/0
//多了一条194网段的路由，类型IA（区域间）
r2#sh ip ro
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
C 193.1.1.0/24 is directly connected, Ethernet1/0
C 192.1.1.0/24 is directly connected, Ethernet0/0
O IA 194.1.1.0/24 [110/20] via 193.1.1.3, 00:00:06, Ethernet1/0
//多了一条194网段路由，类型为IA（区域间）
r3#sh ip ro
3.0.0.0/24 is subnetted, 1 subnets
C 3.3.3.0 is directly connected, Loopback0
C 193.1.1.0/24 is directly connected, Ethernet1/0
O 192.1.1.0/24 [110/20] via 193.1.1.2, 00:02:56, Ethernet1/0
C 194.1.1.0/24 is directly connected, Ethernet0/0
//R3的192路由原本为IA类型（区域间），现在转为O类型（区域内），说明R3认为自已与192网段是直连的。虚链路相当于将R3直接连接了AREA 0 与 AREA 4区域
r4#sh ip ro
4.0.0.0/24 is subnetted, 1 subnets
C 4.4.4.0 is directly connected, Loopback0
O IA 193.1.1.0/24 [110/20] via 194.1.1.3, 00:03:40, Ethernet0/0
O IA 192.1.1.0/24 [110/30] via 194.1.1.3, 00:03:25, Ethernet0/0
C 194.1.1.0/24 is directly connected, Ethernet0/0
//R4上192路由类型IA（区域间）
最后我们将虚链路效果再与正常连接方式进行一下比对，如下图：
验证如下：
r1#sh ip ro
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
O IA 193.1.1.0/24 [110/20] via 192.1.1.2, 00:00:41, Ethernet0/0
C 192.1.1.0/24 is directly connected, Ethernet0/0
C 192.2.2.0/24 is directly connected, Ethernet1/0
O IA 194.1.1.0/24 [110/20] via 192.2.2.4, 00:00:39, Ethernet1/0
r2#sh ip ro
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
C 193.1.1.0/24 is directly connected, Ethernet1/0
C 192.1.1.0/24 is directly connected, Ethernet0/0
O 192.2.2.0/24 [110/20] via 192.1.1.1, 00:01:04, Ethernet0/0
O IA 194.1.1.0/24 [110/30] via 192.1.1.1, 00:00:03, Ethernet0/0
r2#
r3#sh ip ro
3.0.0.0/24 is subnetted, 1 subnets
C 3.3.3.0 is directly connected, Loopback0
C 193.1.1.0/24 is directly connected, Ethernet1/0
O IA 192.1.1.0/24 [110/20] via 193.1.1.2, 00:01:31, Ethernet1/0
O IA 192.2.2.0/24 [110/30] via 193.1.1.2, 00:01:15, Ethernet1/0
O IA 194.1.1.0/24 [110/40] via 193.1.1.2, 00:00:15, Ethernet1/0
r4#sh ip ro
4.0.0.0/24 is subnetted, 1 subnets
C 4.4.4.0 is directly connected, Loopback0
O IA 193.1.1.0/24 [110/30] via 192.2.2.1, 00:00:39, Ethernet1/0
O 192.1.1.0/24 [110/20] via 192.2.2.1, 00:01:37, Ethernet1/0
C 192.2.2.0/24 is directly connected, Ethernet1/0
C 194.1.1.0/24 is directly connected, Ethernet0/0
r5#sh ip ro
5.0.0.0/24 is subnetted, 1 subnets
C 5.5.5.0 is directly connected, Loopback0
O IA 193.1.1.0/24 [110/40] via 194.1.1.4, 00:00:52, Ethernet0/0
O IA 192.1.1.0/24 [110/30] via 194.1.1.4, 00:00:52, Ethernet0/0
O IA 192.2.2.0/24 [110/20] via 194.1.1.4, 00:00:52, Ethernet0/0
C 194.1.1.0/24 is directly connected, Ethernet0/0
如果上述方式还不容易理解，你也可以将virtual-link可以想象成：将R2与R3合并成一台路由器，如下图：
r1#sh ip ro
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback0
O IA 193.1.1.0/24 [110/20] via 192.1.1.2, 00:00:57, Ethernet0/0
C 192.1.1.0/24 is directly connected, Ethernet0/0
O IA 194.1.1.0/24 [110/74] via 192.1.1.2, 00:00:24, Ethernet0/0
r2#sh ip ro
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
C 193.1.1.0/24 is directly connected, Ethernet1/0
C 192.1.1.0/24 is directly connected, Ethernet0/0
C 194.1.1.0/24 is directly connected, Serial2/0
r3#sh ip ro
3.0.0.0/24 is subnetted, 1 subnets
C 3.3.3.0 is directly connected, Loopback0
C 193.1.1.0/24 is directly connected, Ethernet1/0
O IA 192.1.1.0/24 [110/20] via 193.1.1.2, 00:01:06, Ethernet1/0
O IA 194.1.1.0/24 [110/74] via 193.1.1.2, 00:00:37, Ethernet1/0
r4#sh ip ro
4.0.0.0/24 is subnetted, 1 subnets
C 4.4.4.0 is directly connected, Loopback0
O IA 193.1.1.0/24 [110/74] via 194.1.1.2, 00:00:17, Serial2/0
O IA 192.1.1.0/24 [110/74] via 194.1.1.2, 00:00:17, Serial2/0
C 194.1.1.0/24 is directly connected, Serial2/0