基于WPF开发局域网聊天工具，在用udp做上线功能时遇到的问题

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Net.Sockets;
using System.Threading;
using System.Net;

namespace LANTransfer
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        
        private Thread td;
        //private Thread td2;

        public MainWindow()
        {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            td = new Thread(new ThreadStart(startListen));
            td.IsBackground = true;
            td.Start();
            sendOnline();
        }

        private void startListen()
        {
            
            try
            {
                while (true)
                {
                    IPEndPoint RemoteIpEndPoint = new IPEndPoint(IPAddress.Any, 0); 
 
                    UdpClient udpListener = new UdpClient(new IPEndPoint(IPAddress.Any, 3828));
                    string receive = "";
                    byte[] bytes = udpListener.Receive(ref RemoteIpEndPoint);

                    string localAddress = new IPAddress(Dns.GetHostByName(Dns.GetHostName()).AddressList[0].Address).ToString();
                    udpListener.Close();
                    if (localAddress == RemoteIpEndPoint.Address.ToString())
                    {
                        continue;
                    }
                    
                    sendOnline();
                    receive = RemoteIpEndPoint.Address.ToString() + Encoding.UTF8.GetString(bytes);
                    this.Dispatcher.Invoke(new Action(delegate { textBox1.Text = receive; }));
                }
            }
            catch (Exception e)
            {
                MessageBox.Show("侦听出错！"+e.Message);
            }

        }

        private void sendOnline() 
 
        {
            try
            {
                IPEndPoint localPoint = new IPEndPoint(new IPAddress(Dns.GetHostByName(Dns.GetHostName()).AddressList[0].Address), 3828);
                UdpClient onlineMess = new UdpClient(localPoint);
                onlineMess.Connect(IPAddress.Broadcast, 3828);
                byte[] bytes = Encoding.UTF8.GetBytes("我上线了！");
                onlineMess.Send(bytes, bytes.Length);
                onlineMess.Close();
                this.Dispatcher.Invoke(new Action(delegate { textBox2.Text = "已广播上线信息！"; }));                
            }
            catch (Exception e)
            {
                MessageBox.Show("发送上线失败！"+e.Message);
            }
        }

        private void sendOffline()
        {
            try
            {
                IPEndPoint localPoint = new IPEndPoint(new IPAddress(Dns.GetHostByName(Dns.GetHostName()).AddressList[0].Address), 3828);
                UdpClient offlineMess = new UdpClient(localPoint);
                offlineMess.Connect(IPAddress.Broadcast, 3838);
                byte[] bytes = Encoding.UTF8.GetBytes("我下线了！"); 
 
                offlineMess.Send(bytes, bytes.Length);
                offlineMess.Close();
            }
            catch (Exception e)
            {
                MessageBox.Show("发送下线失败！"+e.Message);
            }
        }

        private void Window_Closed(object sender, EventArgs e)
        {
            sendOffline();
        }
    }
}

问题说明一下：我先在虚拟机上和物理机上做了实验（都是win7系统），物理机发的广播虚拟机可以收到，而虚拟机发的广播在物理机收不到。然后我在另一台物理机上做了实验（和我自己的机子在同一局域网，xp系统），就抛出“通常每个套接字地址(协议/网络地址/端口)只允许使用一次”异常，并且连广播都没有发出去。刚接触网络编程，请高手赐教。。。
[解决办法]
参见 http://www.cnblogs.com/xiaozhi_5638/p/3169641.html

局域网UDP通信