How to prevent dede website DDos from being attacked

if($cfg_anquan_cc == 'Y'){
//php防CC攻击 在3秒内连续刷新页面5次以上将指向本机 //www.jb51.net/404.htm
 
$P_S_T = $t_array[0] + $t_array[1];
$timest amp = time();
session_start();
$ll_nowtime = $timestamp ;
if (session_is_registered('ll_lasttime')){
$ll_lasttime = $_SESSION['ll_lasttime'];
$ll_times = $_SESSION['ll_times'] + 1;
$_SESSION['ll_times'] = $ll_times;
}else{
$ll_lasttime = $ll_nowtime;
$ll_times = 1;
$_SESSION['ll_times'] = $ll_times;
$_SESSION['ll_lasttime'] = $ll_lasttime;
}
if (($ll_nowtime - $ll_lasttime)<3){
if ($ll_times>=5){
header(sprintf("Location: %s",&#39;//www.jb51.net/404.htm&#39;));
exit;
}
}else{
$ll_times = 0;
$_SESSION[&#39;ll_lasttime&#39;] = $ll_nowtime;
$_SESSION[&#39;ll_times&#39;] = $ll_times;
}
}