problem to ping an IP address although it works on my LAN

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.Windows.Forms;

namespace NetServer
{
  public delegate object ClientConnectHandler(Socket datasocket);
  public delegate void DataReceivedHandler(object obj,byte[] data);
  public delegate void ClientDisconnectHandler(object obj);

  public class TCPServer
  {
    public event ClientConnectHandler WhenClientConnect;
    public event DataReceivedHandler WhenDataReceived;
    public event ClientDisconnectHandler WhenClientDisconnect;
    Socket ConnectionSocket;
    IPEndPoint Endpoint;
    byte[] Data=new byte[10000];
    object obj=new object();
    List OnlineClients = new List();

    public TCPServer()
    {
      ConnectionSocket = new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
      Endpoint = new IPEndPoint(IPAddress.Parse(Dns.GetHostByName(Dns.GetHostName()).AddressList[0].ToString()),6666);
    }

    public TCPServer(string ip, int port)
    {
      ConnectionSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
      Endpoint = new IPEndPoint(IPAddress.Parse(ip), port);
    }

    public void Listen()
    {
      ConnectionSocket.Bind(Endpoint);
      ConnectionSocket.Listen(100);
      ConnectionSocket.BeginAccept(new AsyncCallback(OnClientConnect), null);
    }

    public void OnClientConnect(IAsyncResult result)
    {
      Socket s = ConnectionSocket.EndAccept(result);
      OnlineClients.Add(s);
      if (WhenClientConnect != null)
        obj = WhenClientConnect(s);
      ConnectionSocket.BeginAccept(new AsyncCallback(OnClientConnect), null);
      s.BeginReceive(Data, 0, Data.Length, SocketFlags.None, new AsyncCallback(OnDataReceived), new SSocket { Object=obj , Socket=s});
    }

    public void OnDataReceived(IAsyncResult result)
    {
      SSocket ssocket = (SSocket)result.AsyncState;
      try
      {
        int size = ssocket.Socket.EndReceive(result);
        if (WhenDataReceived != null)
          WhenDataReceived(ssocket.Object, Data.Take(size).ToArray());
        Data = new byte[10000];
        ssocket.Socket.BeginReceive(Data, 0, Data.Length, SocketFlags.None, new AsyncCallback(OnDataReceived), new SSocket { Object = obj, Socket = ssocket.Socket });
      }
      catch(SocketException ex)
      {
        if(ex.ErrorCode == 10054)
        {
          foreach (Socket item in OnlineClients)
            if (ssocket.Socket == item)
              OnlineClients.Remove(item);
          if (WhenClientDisconnect != null)
            WhenClientDisconnect(ssocket.Object);
        }
      }
    }
  
    public void Send(Socket socket,byte[] data)
    {
      if(socket!=null)
        socket.Send(data);
    }
  }

  public class SSocket
  {
    object obj;
    public object Object
    {
      get { return obj; }
      set { obj = value; }
    }
 
    Socket socket;

    public Socket Socket
    {
      get { return socket; }
      set { socket = value; }
    }
  }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.Sockets;
using System.Net;
using System.Windows.Forms;

namespace NetClientTest
{
  public delegate void DataReceivedHandler(byte[] data);

  public class TCPClient
  {
    byte[] data = new b