unit DropAllU;
{
Aufruf:
  InstallFW('192.168.0.2');

und zum schluss:
  RemoveFW;
}

interface

   procedure InstallFW(MyIP: String);
   procedure RemoveFW;

implementation

uses Windows;

const
     IPHLPAPI = 'IPHLPAPI.DLL';

type
  PFFORWARD_ACTION = Integer;
  PPFFORWARD_ACTION = ^PPFFORWARD_ACTION;
  //
  INTERFACE_HANDLE = Pointer;
  //
  PFADDRESSTYPE = Integer;
  PPFADDRESSTYPE = ^PFADDRESSTYPE;
  //
  TByteArray = Array [0..Pred(MaxInt)] of Byte;
  PByteArray = ^TByteArray;
  TIpBytes = Array [0..3] of Byte;

const
  PF_ACTION_DROP = 1;

const
  PF_IPV4 = 0;

function PfCreateInterface(
           dwName: DWORD;
           inAction: PFFORWARD_ACTION;
           outAction: PFFORWARD_ACTION;
           bUseLog: BOOL;
           bMustBeUnique: BOOL;
           var ppInterface: INTERFACE_HANDLE): DWORD;
           stdcall; external IPHLPAPI name '_PfCreateInterface@24';

function PfDeleteInterface(
           pInterface: INTERFACE_HANDLE): DWORD;
           stdcall; external IPHLPAPI name '_PfDeleteInterface@4';

function PfBindInterfaceToIPAddress(
           pInterface: INTERFACE_HANDLE;
           pfatLinkType: PFADDRESSTYPE;
           IPAddress: PByteArray): DWORD;
           stdcall; external IPHLPAPI name '_PfBindInterfaceToIPAddress@12';

function PfUnBindInterface(
           pInterface: INTERFACE_HANDLE): DWORD;
           stdcall; external IPHLPAPI name '_PfUnBindInterface@4';

var
   Handle_Interface : INTERFACE_HANDLE = nil;

function StrToInt(S: PChar): Integer;
begin
   Result := 0;
   if S = '' then Exit;
   while S^ in ['0'..'9'] do begin
      Result := Result * 10 + Integer(S^) - Integer('0');
      Inc( S );
   end;
end;

function StrToIpBytes( IpStr: String ): TIpBytes;
var N : Integer;
begin
   N := 0;
   while Pos('.', IpStr)>0 do begin
      Result[N] := StrToInt(@Copy(IpStr, 1, Pos('.', IpStr) - 1)[1]);
      Delete(IpStr, 1, Pos('.', IpStr));
      Inc(N);
   end;
   Result[N] := StrToInt(@IpStr[1]);
end;

procedure InstallFW(MyIP: String);
var
   IpLocal : TIpBytes;
begin
   if (MyIP <> '') and Not Assigned(Handle_Interface) then begin
      FillChar(IpLocal, 4, #0);
      IpLocal := StrToIpBytes(MyIP);

      PfCreateInterface(0, PF_ACTION_DROP, PF_ACTION_DROP, False, False, Handle_Interface);
      PfBindInterfaceToIPAddress(Handle_Interface, PF_IPV4, @ipLocal);
   end;
end;

procedure RemoveFW;
begin
   if Assigned(Handle_Interface) then begin
      PfUnBindInterface(Handle_Interface);
      PfDeleteInterface(Handle_Interface);
      Handle_Interface := nil;
   end;
end;

end.