My code is below and the platform is Win2K3 R2:

using System;
using System.Net;
using System.Net.Sockets;
using System.Threading;

namespace TechUDPBroadcast {
 class Program {
     static void Main(string[] args) {
         const string addr = "224.1.3.99";
         const int prt = 12799;

         UdpClient udpc = new UdpClient();
         udpc.Client.SetSocketOption(SocketOptionLevel.Socket,
                           SocketOptionName.ReuseAddress, true);
         udpc.Client.Bind(new IPEndPoint(IPAddress.Any, prt));
         udpc.EnableBroadcast = true;

         udpc.JoinMulticastGroup(IPAddress.Parse(addr));

         ManualResetEvent abort = new ManualResetEvent(false);
         WaitHandle[] evs = new WaitHandle[2];
         evs[0] = abort;
         ThreadPool.QueueUserWorkItem(new WaitCallback(delegate {
             while (true) {
                 IAsyncResult asy = udpc.BeginReceive(
                       new AsyncCallback(delegate(IAsyncResult iasy) {
                     IPEndPoint rp = null;
                     byte[] recv = udpc.EndReceive(iasy, ref rp);
                     Console.Write(".");
                 }), null);
                 evs[1] = asy.AsyncWaitHandle;
                 if (WaitHandle.WaitAny(evs) == 0) return;
             }
         }));
         ThreadPool.QueueUserWorkItem(new WaitCallback(delegate {
             for (int i = 0; i < 1000; i++) {
                 udpc.Send(new byte[] { 0x1, 0x2 }, 2,
                             new IPEndPoint(IPAddress.Parse(addr), prt));
                 Console.Write("+");
                 Thread.Sleep(1000);
                 if (abort.WaitOne(0, false)) return;
             }
         }));
         Console.ReadKey();
         Abort.Set();
     }
 }
}

The code is simple and has no tricky. UdpClient broadcast
datagram every second, another thread receive it asynchorously.
When it is running at LAN, sending & receiving are OK.
Then i connect the PC to Internet, the UdpClient stop receiving!
This happened with or without Windows FireWall.

Is this a bug of DotNetFramework?

greenxiar