Depressed sendto failure

Depressed a morning, the original sendto return invalid arguments reason is to bind the socket to the 127.0.0.1.
Did not pay attention to this problem, has been looking for IP is not write wrong ...
127.0.0.1 can only be sent to this machine, including the native IP, so the native test is normal, and the proxy check needs to be contracted to the external machine, resulting in a sendto return error.

This condition may be detected when the system is called and returns an error

However, similar, the network IP is bound, the network IP access, but will not return errors, because the intranet may be accessed through the gateway to the external network