How to Know Which Ports of a Computer Is Open or Closed?

Code:

This is my PortScanner class:

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

 public class PortScanner
 {
     public string Host { get; set; }

     public PortScanner(string host)
     {
         this.Host = host;
     }

     public ScannerResult Scan(int fromPort, int toPort)
     {
         var result = new ScannerResult();

         for (int portNumber = fromPort; portNumber <= toPort; portNumber++)
         {
             if (IsPortOpen(portNumber))
                 result.OpenPorts.Add(portNumber.ToString());

             else result.ClosedPorts.Add(portNumber.ToString());
         }

         return result;
     }

  public int FindFirstOpenPort(int fromPort, int toPort)
    {        
        for (int portNumber = fromPort; portNumber <= toPort; portNumber++)
        {
            if (IsPortOpen(portNumber))
                return portNumber;
        }
        return 0;
    }

private static int FindFreePort()
       {
           int port = 0;

           IPEndPoint endPoint = new IPEndPoint(IPAddress.Any, 0);
           using (Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
           {
               socket.Bind(endPoint);
               IPEndPoint local = (IPEndPoint)socket.LocalEndPoint;
               port = local.Port;
           }

           if (port == 0)
               throw new InvalidOperationException("Unable to find a free port.");

           return port;
       }

     public bool IsPortOpen(int port)
     {
         Socket socket = null;
         try
         {
             // Make a TCP-based socket
             socket = new Socket(AddressFamily.InterNetwork,
                             SocketType.Stream,
                             ProtocolType.Tcp);
             // Connect
             socket.Connect(host, port);
             return true;
         }
         catch (SocketException se)
         {
             if (se.SocketErrorCode == SocketError.ConnectionRefused)
             {
                 return false;
             }
             else
             {
                 // An error occurred when attempting to access the socket
                 Debug.WriteLine(se.ToString());
                 Console.WriteLine(se.ToString());
             }
         }
         finally
         {
             if (socket != null)
             {
                 if (socket.Connected)
                     socket.Disconnect(false);
                 socket.Close();
             }
         }
         return false;
     }

 }

This is my ScannerResult class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

class ScannerResult
 {
     public List<string> OpenPorts = new List<string>();
     public List<string> ClosedPorts = new List<string>();
 }

And this is how to use it:

var portScanner = new PortScanner("127.0.0.1");
var result = portScanner.Scan(1, 65535);