start_addr := inet_addr('127.0.0.1');
stop_addr := inet_addr('127.0.255.255');

while start_addr <> stop_addr do
begin
 выполняешь свои действия
 asm
  mov eax, start_addr
  bswap eax
  inc eax
  bswap eax
  mov start_addr, eax
 end;
end;

  function IpToInt(ip: string): dword; // превращаем IP в число
  begin
    result := inet_addr(PChar(ip));
    result := (result shl 24) or (result and $FF00 shl 8) or
              (result and $FF0000 shr 8) or (result shr 24);
  end;

  function IntToIP(i: DWORD): string;  // число в IP
  var kk: DWORD;
  begin
    kk:=(i shl 24) or (i and $FF00 shl 8) or
        (i and $FF0000 shr 8) or (i shr 24);
    Result:= inet_ntoa(in_addr(kk))
  end;

  procedure Scan;
  begin
    AddrTo:=IpToInt(IpTo); AddrFrom:=IpToInt(IpFrom);
    for i:=AddrTo to AddrFrom do ping_addr(IntToIp(i));
  end;