How yo get the systems mac Id

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C#

Below is my code:

protected string FetchMac()
   {
       string macAddr= "";

           foreach (NetworkInterface nic in NetworkInterface.GetAllNetworkInterfaces())
           {
               if (nic.OperationalStatus == OperationalStatus.Up)
               {
                   macAddresses += nic.GetPhysicalAddress().ToString();
                   break;
               }
           }
           lblMac.Text = macAddr.ToString();
           return macAddr;
       }
   }

This code is working fine for me at local host it shows different MAC IDs for different systems, but it's not working at server side...
At server side it read all system MAC addresses is same pls please help me.