R1上fa0/0口和R2上fa0/0口相连，
R1 R2的0/1口分别连PC
配IP地址
R1上
int fa0/0
ip add 172.168.3.1 255.255.255.0
no sh
int fa0/1
ip add 172.16.1.1 255.255.255.0
no sh
R2上
int fa 0/0
ip add 172.168.3.2 255.255.255.0
no sh
int fa 0/1
ip add 192.168.1.1 255.255.255.0
no sh
接着指静态路由
R1上
ip route 192.168.1.0 255.255.255.0 172.16.1.1
R2上
ip route 172.16.1.0 255.255.255.0 192.168.1.1
