问题：ping外网出现:
sendto: Network is unreachable
查看：
#route
Route命令 : 在数据包没有有效传递的情况下，可以利用route命令查看路由表
[root@tiny4412:/]#route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 * 255.255.255.0 U eth0
发现，是由于网关，没有配置网关（gateway）
解决：
[root@tiny4412:/]#route add default gw 192.168.1.1
[root@tiny4412:/]#route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default 192.168.1.1 0.0.0.0 UG eth0
192.168.1.0 * 255.255.255.0 U eth0
测试：
[root@tiny4412:/]#ping 119.75.217.56
PING 119.75.217.56 (119.75.217.56): data bytes
bytes from 119.75.217.56: seq= ttl= time=20.468 ms
bytes from 119.75.217.56: seq= ttl= time=19.113 ms
bytes from 119.75.217.56: seq= ttl= time=18.814 ms
bytes from 119.75.217.56: seq= ttl= time=18.906 ms
bytes from 119.75.217.56: seq= ttl= time=18.859 ms
bytes from 119.75.217.56: seq= ttl= time=18.704 ms
bytes from 119.75.217.56: seq= ttl= time=19.050 ms
bytes from 119.75.217.56: seq= ttl= time=20.514 ms
bytes from 119.75.217.56: seq= ttl= time=21.355 ms
^C
--- 119.75.217.56 ping statistics ---
packets transmitted, packets received, % packet loss
round-trip min/avg/max = 18.704/19.531/21.355 ms