How to get Mac Address of Remote Computer

Question

Hi All,
I tried to find out a solution for finding Mac Address of a remote system, then first i tried with finding it with local address using the following code it works fine for me.
public class MacAddressFinder {
     public static void main(String[] args) {
          try
               InetAddress ipAddr = InetAddress.getLocalHost();
               System.out.println("Current IP address : " + ipAddr.getHostAddress());
               NetworkInterface nwIntf;
               try
                    nwIntf = NetworkInterface.getByInetAddress(ipAddr);
                    byte[] hwAddr = nwIntf.getHardwareAddress();
                    System.out.print("Current MAC address : ");
                    StringBuilder sb = new StringBuilder();
                    for (int i = 0; i < hwAddr.length; i++)
                         sb.append(String.format("%02X%s", hwAddr, (i < hwAddr.length - 1) ? "-" : ""));          
                    System.out.println(sb);
               } catch (SocketException e) {
                    e.printStackTrace();
          catch (UnknownHostException e) {
               e.printStackTrace();
But when i tried this piece of code in jsp with the following code i am getting NeworkInterface object value as null and there by i am unable to get the Mac Address of a remote computer.
InetAddress ipAddr = InetAddress.getByName(request.getRemoteAddr());
NetworkInterface nwIntf = NetworkInterface.getByInetAddress(ipAddr);Can you please suggest me how to find out the Mac address of remote system?
Thanks,
Uday

Answer 1

first of all, NetworkInterface only exposes the NetworkInterfaces of the local computer. secondly, you cannot find the mac address of an arbitrary remote computer. that information is not available outside of the local subnet. and java doesn't expose a way to discover it even for computers on the local subnet.