private void button3_Click(object sender, EventArgs e)
        {
            Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            //这时的IP无论填多少（除了0.0.0.0), 都可以连接成功
            //但只要改了端口就连接不上了
            client.BeginConnect("10.40.60.70", 80, new AsyncCallback(Callback), client);
        }

        private void Callback(IAsyncResult async)
        {
            Socket client = async.AsyncState as Socket;
            try
            {
                client.EndConnect(async);
                //连接成功
                Console.WriteLine("connect successed");
            }
            catch (Exception ex)
            {
                //连接失败
                Console.WriteLine(ex.Message);
            }
        }