r00tsecurity -> Source Code Center :: PHP Based DoS Blocker

<?php
    define ('BLACKLIST','black.list');
 
    $list=file(BLACKLIST);
 
    foreach ($list as $addr)  {
            $addr=trim($addr);
            $host_addr=$_SERVER['REMOTE_ADDR'];
 
            // Semplice indirizzo IP
            if ($host_addr==$addr)
                    die ("Your IP is {$addr} and you're not allowed to view this page\n");
 
            // Subnet di classe C
            else if (preg_match('/(\d+\.\d+\.\d+)\.0\/24/',$addr,$sub))  {
                    $subnet=trim($sub[1]);
 
                    if (preg_match("/^{$subnet}/",$host_addr))
                            die ("Your IP is {$host_addr} and you're not allowed to view this page\n");
            }
 
            // Subnet di classe B
            else if (preg_match('/(\d+\.\d+)\.0\.0\/16/',$addr,$sub))  {
                    $subnet=trim($sub[1]);
 
                    if (preg_match("/^{$subnet}/",$host_addr))
                            die ("Your IP is {$host_addr} and you're not allowed to view this page\n");
            }
 
            // Subnet di classe A
            else if (preg_match('/(\d+)\.0\.0\.0\/8/',$addr,$sub))  {
                    $subnet=trim($sub[1]);
 
                    if (preg_match("/^{$subnet}/",$host_addr))
                            die ("Your IP is {$host_addr} and you're not allowed to view this page\n");
            }
    }
    ?>