Question

I found this great code on MSDN for a UDP Client/Server connection, however the client can only send to the server, it cant reply back. How can I make this so the server can respond to the client that send the message.
The Server

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.IO;
using System.Security.Cryptography;


namespace UDP_Server
{
    class Program
    {
        private const int listenPort = 11000;

        private static void StartListener()
        {
            bool done = false;

            UdpClient listener = new UdpClient(listenPort);
            IPEndPoint groupEP = new IPEndPoint(IPAddress.Any, listenPort);
            try
            {
                while (!done)
                {
                    Console.WriteLine("Waiting for broadcast");
                    byte[] bytes = listener.Receive(ref groupEP);
                    Console.WriteLine("Received broadcast from {0} :\n {1}\n",groupEP.ToString(), Encoding.ASCII.GetString(bytes, 0, bytes.Length));
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }
            finally
            {
                listener.Close();
            }
        }

        public static int Main()
        {
            StartListener();

            return 0;
        }
    }

}

And the client

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.IO;
using System.Security.Cryptography;

namespace UDP_Client
{
    class Program
    {
        static void Main(string[] args)
        {
            Send("TEST STRING");
            Console.Read();
        }
        static void Send(string Message)
        {
            Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
            IPAddress broadcast = IPAddress.Parse("10.1.10.117");
            byte[] sendbuf = Encoding.ASCII.GetBytes(Message);
            IPEndPoint ep = new IPEndPoint(broadcast, 11000);
            s.SendTo(sendbuf, ep);
        }
    }
}

Answer 1

Just do it the other way round. Call StartListener on the client and it can receive udp data like a server.

On your server just send data with the clients code.