使用默认缺省路由让PCA网络访问internet:

[RTA]interface S6/0

          ip address 192.168.1.1 24

          interface g0/0

          ip address 192.168.3.1

[RTB]interface S6/0

          ip address 192.168.1.2 24

          interface g0/0

          ip address 192.168.2.1 24

          ip route-static 192.168.3.0  255.255.255.0 192.168.1.1

PCA:192.168.3.2 255.255.255.0

PCB:192.168.2.2 255.255.255.0

现在如果PCA所在网段属于私网，想要访问公网PCB，此时可在RTA上做一条静态缺省路由：

[RTA]ip route-static 0.0.0.0 0.0.0.0 192.168.1.2      缺省路由使用0来匹配，因为不是点到点串口连接所以使用下一跳地址作为出口。

此时PCA能够访问internetPCB：

C:\Documents and Settings\xiaofei>ping 192.168.2.2

Pinging 192.168.2.2 with 32 bytes of data:

Reply from 12.1.1.2: bytes=32 time=1ms TTL=254

Reply from 12.1.1.2: bytes=32 time=2ms TTL=254
Reply from 12.1.1.2: bytes=32 time=1ms TTL=254
Reply from 12.1.1.2: bytes=32 time=1ms TTL=254

Ping statistics for 192.168.2.2:

    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 1ms, Maximum = 2ms, Average = 1ms