gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.Sockets;

namespace TCPPunch
{
    class Program
    {
        static void Main(string[] args)
        {
            var port = 4119;
            var l = new TcpListener(System.Net.IPAddress.Any, port);
            l.Start();
            try
            {
                var o = new TcpClient(new System.Net.IPEndPoint(System.Net.IPAddress.Any, port));
                var sdf = o.Client.LocalEndPoint;
                o.Connect("mysite.com", 80);
            }
            catch(Exception ee) { 
            }
            var e = l.AcceptSocket();
            Console.WriteLine(e.RemoteEndPoint.AddressFamily);
        }
    }
}