先將R1,R2,R3互相ping通。
R1:
R1(config)#interface tunnel 0
R1(config-if)#tunnel mode gre ip
R1(config-if)#ip address 172.16.0.1 255.255.255.0
R1(config-if)#tunnel source 192.168.1.1
R1(config-if)#tunnel destination 192.168.2.2
R1(config-if)#exit
R1(config)#ip route 0.0.0.0 0.0.0.0 172.16.0.2
R3:
R3(config)#interface tunnel 0
R3(config-if)#tunnel mode gre ip
R3(config-if)#ip address 172.16.0.2 255.255.255.0
R3(config-if)#tunnel source 192.168.2.2
R3(config-if)#tunnel destination 192.168.1.1
R3(config-if)#exit
R3(config)#ip route 0.0.0.0 0.0.0.0 172.16.0.1