Dynamic DNS Iptables Firewall Script

I’m using my computer as a development platform and I usually let people in by editing my firewall active table

but for those with dynamic ip addresses I had to figure out a different solution

so I made a small script in PHP to check for my friends dynamic ip address by looking up his dyndns.org hostname

it checks IP then goes sleeping for 5 minutes

when it detects an ip change it updates firewall by flushing my firends chain and adding a rule to let him access my webserver

this script works in my firewall iptables setup, it could work on yours but you have to be smart and figure that out for yourself, I’m not giving any guaranteess for this, use it as GPL V3 code :)
if you want me to help you set it up, just contact me

here’s the code:

use this code as GPL V3 licence says
Copyright (C) 2008, Miroslav Madzarevic, All Rights Reserved
$old_ip = '';

while (1) {

    sleep (300);

    $host = 'friend.dyndns.org';

    if (!preg_match('/^'.$host.' has address ((?:\d{1,3}\.){3}\d{1,3})$/',
           exec ("/usr/bin/host $host"), $matches)) {
        echo "IP problems\n";

    $ip = $matches[1];

    $ip_parts = preg_split ('/\./', $ip, -1, PREG_SPLIT_NO_EMPTY);

    if (count($ip_parts) != 4) {
        echo "wrong ip parts count\n";

    $good = array();

    foreach ($ip_parts as $ip_part) {
        $ip_part = (int) $ip_part;
        if ($ip_part < 1 or $ip_part > 254) {
            echo "wrong ip part, $ip_part\n";
        $good[] = $ip_part;

    $new_ip = join('.', $good);

    if ($old_ip != $new_ip) {

        `/sbin/iptables -F friend`;

        `/sbin/iptables -A friend -s $new_ip/32 -p tcp -m tcp --dport 80 -j ACCEPT`;

        $old_ip = $new_ip;


fastcgi mod_fcgid

I’ve been playing a little on my cPanel hosting trying to get maximum speed while also enforcing security at running php scripts

I first started with security running mod_suphp and while it worked fine it lacked the speed of the DSO php (mod_php)

so I read a thing or two about fastcgi and enabled it

I’m pleasantly surprised by the speed of the hosting

each user got its own persistent php application running requests (actually it’s limited to 500 php requests per php5 process by MaxRequestsPerProcess 500 directive)

I’m keeping an eye about the memory consumption but I hope I’ll be able to keep running with this setup

and while I got php running as the actuall cPanel user, apache is still running as nobody for other requests… hmmm… I’m using apache 2.2 with MPM Prefork… maybe I should try a different MPM?