java - Android UDP can't receive from outside LAN

Question

My code can't receive UDP messages from outside my home net. The communication is between Android and Java computer application, with IP inside my LAN (for example 192.168.0.3) the code works, if I put my Java computer application inside my online server (and obviously I changed every IP with external IPs) this doesn't work; Android can send but it can't receive.

Android code :

@Override
protected Integer doInBackground(Void... params) {
    DatagramSocket socket = null;
    byte[] buf = new byte[1024];
    DatagramPacket packet = new DatagramPacket(buf, buf.length);
    try {
        socket = new DatagramSocket(25565);
    } catch (Exception e) {
        Log.i("Ex ", "");
    }
    while (true) {
        try {
            socket.receive(packet);
            String message = new String(packet.getData(), 0,packet.getLength());
            Log.i("message", "" + message);
        } catch (IOException e) {
            Log.i("IO Ex", "");
        }
        catch (Exception e){
        }
    }
}

Java computer application code : http://pastebin.com/2hVGeP6R

Answer 1

192.168.0.X is an internal NAT address. Any network can use it, but it can't be reached from anywhere outside. You either need to configure your router to pass it through to your PC and hit the router's external IP, or you need a real network address.