[barakuda]

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Código Delphi [-]
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, winsock,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Label1: TLabel;
    Edit1: TEdit;
    Label2: TLabel;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

type
  PULONG = ^ULONG;

var
  Form1: TForm1;

implementation

{$R *.dfm}

function SendARP(DestIP,SrcIP: in_addr; pMacAddr,PhyAddrLen: PULONG): DWORD;
  stdcall; external 'iphlpapi.dll' name 'SendARP';

function ObtenerMAC(IP: Ansistring): Ansistring;
var
  i: Integer;
  dwRetVal: DWORD;
  DestIp, SrcIp: in_addr;
  MacAddr: array[0..1] of ULONG;
  PhysAddrLen: ULONG;
  PhysAddr: PByte;
begin
    DestIp.S_addr:= 0;
    SrcIp.S_addr:= 0;
    PhysAddrLen:= 6;
    DestIp.S_addr:= inet_addr(PAnsiChar(AnsiString(IP)));

    dwRetVal:= SendARP(DestIp, SrcIp, @MacAddr, @PhysAddrLen);

    Result:= EmptyStr;
    if dwRetVal = NO_ERROR then
    begin
      PhysAddr:= PByte(@MacAddr);
      for i := 1 to Sizeof(MacAddr)-2 do
      begin
        if Result= EmptyStr then
          Result:= IntToHex(PhysAddr^,2)
        else
          Result:= Result + '-' + IntToHex(PhysAddr^,2);
        inc(PhysAddr);

      end;
    end;
    end;

procedure TForm1.Button1Click(Sender: TObject);
begin

label1.Caption:=ObtenerMAC(edit1.Text);
end;

end.