How to get client's MAC Address in Asp.Net

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C#

ASP.NET

I want to get Client's MAC address for User Account Authentication. I searched every where and found the code to get Server's MAC Address only which is not my requirement. I want to access the MAC Address of a device where the Website will be accessed. Finally I found the code but It is not getting my Local/Server System MAC, it is getting the same MAC for all devices. The code is:

[DllImport("Iphlpapi.dll")]
       private static extern int SendARP(Int32 dest, Int32 host, ref Int64 mac, ref Int32 length);
       [DllImport("Ws2_32.dll")]
       private static extern Int32 inet_addr(string ip);
       protected void Page_Load(object sender, EventArgs e)
       {
           try
           {
               string userip = Request.UserHostAddress;
               string strClientIP = Request.UserHostAddress.ToString().Trim();
               Int32 ldest = inet_addr(strClientIP);
               Int32 lhost = inet_addr("");
               Int64 macinfo = new Int64();
               Int32 len = 6;
               int res = SendARP(ldest, 0, ref macinfo, ref len);
               string mac_src = macinfo.ToString("X");
               if (mac_src == "0")
               {
                   if (userip == "127.0.0.1")
                       Response.Write("visited Localhost!");
                   else
                       Response.Write("the IP from" + userip + "" + "<br>");
                   return;
               }

               while (mac_src.Length < 12)
               {
                   mac_src = mac_src.Insert(0, "0");
               }

               string mac_dest = "";

               for (int i = 0; i < 11; i++)
               {
                   if (0 == (i % 2))
                   {
                       if (i == 10)
                       {
                           mac_dest = mac_dest.Insert(0, mac_src.Substring(i, 2));
                       }
                       else
                       {
                           mac_dest = "-" + mac_dest.Insert(0, mac_src.Substring(i, 2));
                       }
                   }
               }

               Response.Write("welcome" + userip + "<br>" + ",the mac address is" + mac_dest + "."

                + "<br>");
           }
           catch (Exception err)
           {
               Response.Write(err.Message);
           }
       }

Now Please help me how to get the exactly client's MAC address. Thanks.