GRE隧道构建

1、底层信息配置通，

interface Ethernet0/0
 ip address 192.168.1.1 255.255.255.0
interface Ethernet0/1
 ip address 13.0.0.1 255.255.255.0

R2:

 interface Ethernet0/0
 ip address 23.0.0.2 255.255.255.0
interface Ethernet0/1
 ip address 192.168.2.1 255.255.255.0

R3:

interface Ethernet0/0
 ip address 13.0.0.3 255.255.255.0
interface Ethernet0/1
 ip address 23.0.0.3 255.255.255.0
interface Ethernet0/2
 ip address 34.0.0.3 255.255.255.0

R4:

interface Ethernet0/0
 ip address 34.0.0.4 255.255.255.0

PC1:

interface Loopback0
 ip address 1.1.1.1 255.255.255.0
interface Ethernet0/0
 ip address 192.168.1.2 255.255.255.0

PC2:

interface Loopback0
 ip address 2.2.2.2 255.255.255.0
interface Ethernet0/0
 ip address 192.168.2.2 255.255.255.0

2、配置路由信息

在R1和R2上面配置路由信息，实现建立隧道的双方基于公网环境能够互通，这里通过在R1和R2上面配置默认路由实现。
R1:

 ip route 0.0.0.0 0.0.0.0 13.0.0.3

R2:

 ip route 0.0.0.0 0.0.0.0 23.0.0.3

3、配置Tunnel口

interface Tunnel0
 ip address 12.0.0.1 255.255.255.0
 tunnel source 13.0.0.1
 tunnel destination 23.0.0.2

R2:

interface Tunnel0
 ip address 12.0.0.2 255.255.255.0
 tunnel source 23.0.0.2
 tunnel destination 13.0.0.1

4、完成路由信息，实现PC1可以和PC1互通。

在建立路由时，从R1去往对方私网2的路由，需要指定到隧道接口当中，只有从隧道接口才能实现两个私网之间的互通。
R1:

ip route 1.1.1.0 255.255.255.0 192.168.1.2
ip route 2.2.2.0 255.255.255.0 12.0.0.2
ip route 192.168.2.0 255.255.255.0 12.0.0.2

R2:

ip route 1.1.1.0 255.255.255.0 12.0.0.1
ip route 2.2.2.0 255.255.255.0 192.168.2.2
ip route 192.168.1.0 255.255.255.0 12.0.0.1

PC1:

ip route 0.0.0.0 0.0.0.0 192.168.1.1

PC2：

ip route 0.0.0.0 0.0.0.0 192.168.2.1

5、测试结果

最终要求私网1和私网2能够相互ping通。