Android UDP receive on phone via 3g or wifi

Question

So, I'm testing my android game on my phone (HTC Legend) in debugging mode. I am trying to communicate with my custom JAVA server. I can receive UDP packages on my server, i can see them, but none of the responses from server ever reaches phone. I am using following code on my server to get client IP:port

datagramPackageIn.getAddress();
datagramPackageIn.getPort();

On the client side I use this code to see my address:

public String getLocalIpAddress() {
        try {
            for (Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces(); en.hasMoreElements();) {
                NetworkInterface intf = en.nextElement();
                for (Enumeration<InetAddress> enumIpAddr = intf.getInetAddresses(); enumIpAddr.hasMoreElements();) {
                    InetAddress inetAddress = enumIpAddr.nextElement();
                    if (!inetAddress.isLoopbackAddress()) {
                        return inetAddress.getHostAddress().toString();
                    }
                }
            }
        } catch (SocketException ex) {
            Log.e(TAG, ex.toString());
        }
        return null;
    }

In testing I can see that those 2 addresses are different. Maybe there is the problem?

I used standard UDP communication code (one that worked in emulator) in client:

run(){//simplified  version
while(true)
packageIN()
}
public packageIN(){
DatagramPacket packet= new DatagramPacket(inBuffer, inBuffer.length);
DatagramSocket socket= new DatagramSocket(receivingPort);

socket.receive();
}

So, any working solutions ( tested one with phone on 3g)?

P.S. I know that HTC Legend has wifi problems, thats why I use 3G.....

Answer 1

If the server shows a different IP address than the mobile device when you connect through 3G, you may be behind a NAT gateway. Some cell carriers do this. A sure sign of NAT is if the IP looks something like 10.x.x.x or 192.168.x.x or 172.y.x.x (where yis between 16 and 31). I've also seen carriers assign NAT addresses of the form 1.x.x.x.

With such a setup it depends on how the gateway handles UDP.

To rule out any errors caused by NAT, try accessing the server through WiFi and a LAN, not going through any networks that you don't control.