Sending and Receiving UDP packets

Question

The following code sends a packet on port 15000:

int port = 15000;
UdpClient udp = new UdpClient();
//udp.EnableBroadcast = true;  //This was suggested in a now deleted answer
IPEndPoint groupEP = new IPEndPoint(IPAddress.Broadcast, port);
string str4 = "I want to receive this!";
byte[] sendBytes4 = Encoding.ASCII.GetBytes(str4);
udp.Send(sendBytes4, sendBytes4.Length, groupEP);
udp.Close();

However, it's kind of useless if I can't then receive it on another computer. All I need is to send a command to another computer on the LAN, and for it to receive it and do something.

Without using a Pcap library, is there any way I can accomplish this? The computer my program is communicating with is Windows XP 32-bit, and the sending computer is Windows 7 64-bit, if it makes a difference. I've looked into various net send commands, but I can't figure them out.

I also have access to the computer (the XP one)'s local IP, by being able to physically type 'ipconfig' on it.

EDIT: Here's the Receive function I'm using, copied from somewhere:

public void ReceiveBroadcast(int port)
{
    Debug.WriteLine("Trying to receive...");
    UdpClient client = null;
    try
    {
        client = new UdpClient(port);
    }
    catch (Exception ex)
    {
        Debug.WriteLine(ex.Message);
    }

    IPEndPoint server = new IPEndPoint(IPAddress.Broadcast, port);

    byte[] packet = client.Receive(ref server);
    Debug.WriteLine(Encoding.ASCII.GetString(packet));
}

I'm calling ReceiveBroadcast(15000) but there's no output at all.

Answer 1

Here is the simple version of Server and Client to send/receive UDP packets

Server

IPEndPoint ServerEndPoint= new IPEndPoint(IPAddress.Any,9050);
Socket WinSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
WinSocket.Bind(ServerEndPoint);

Console.Write("Waiting for client");
IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0)
EndPoint Remote = (EndPoint)(sender);
int recv = WinSocket.ReceiveFrom(data, ref Remote);
Console.WriteLine("Message received from {0}:", Remote.ToString());
Console.WriteLine(Encoding.ASCII.GetString(data, 0, recv));

Client

IPEndPoint RemoteEndPoint= new IPEndPoint(
IPAddress.Parse("ServerHostName"), 9050);
Socket server = new Socket(AddressFamily.InterNetwork,
                           SocketType.Dgram, ProtocolType.Udp);
string welcome = "Hello, are you there?";
data = Encoding.ASCII.GetBytes(welcome);
server.SendTo(data, data.Length, SocketFlags.None, RemoteEndPoint);

Answer 2

There is actually a very good UDP example of a server and listener on MSDN: Simple UDP example