View source for Dynamic DNS on private DNS server (Router OS, Bind, Apache, and Shell script)

Original and updates here: [[http://eurekamoment.eu/?p=1283 eurekamoment.eu]]
If you constantly connect to your home network (as I do), you have, on occasion, experienced that frustrating moment when the dynamic dns service is down for whatever reason. Let's assume that you are a person who likes to have more controll over the services you use, and have setup your private DNS server on a cheap VPS like [[https://m.do.co/t/92532cd726c6 DigitalOcean]]. If so, you're at the right place.

For this to work, we will need a smarter router that can fetch http data - Mikrotik in my case, and a private DNS server on the public network hosting your domain and under your control. If you can't access the shell, then you can't complete this tutorial.

<strong>Note that this isn't very secure and I will be modifying the process to get a secure solution</strong>

<strong>Setup</strong>
<ol>
	<li>Setup a web server on your DNS server</li>
	<li>Create a php update page
<pre class="lang:php decode:true " title="deviceupdate.php">&lt;?php
  $ip=$_SERVER[REMOTE_ADDR];
  if ($_GET['hash']="ae2b1fca515949e5d54fb22b8ed95575") {
    file_put_contents("deviceupdate.log","DATE: ".date("Y-m-d H:i:s")." IP: ".$ip."\n",FILE_APPEND | LOCK_EX);
    file_put_contents("homeip.log",$ip,LOCK_EX);
    print "DATE: ".date("Y-m-d H:i:s")." IP: ".$ip;
  }
?&gt;</pre>
</li>
	<li>Setup Mikrotik schetuler that runs every few minutes
<pre class="lang:sh decode:true " title="Mikrotik schedule script">/tool fetch keep-result=no mode=http url="http://www.my-dns-servers-web-server.com/mikrotik/deviceupdate.php?hash=ae2b1fca515949e5d54fb22b8ed95575"</pre>
</li>
	<li>Create a shell script called <strong>dyndns.sh</strong> to update the DNS zone
<pre class="lang:sh decode:true " title="dyndns.sh">#!/bin/bash
newip=$(cat /var/www/homeip.log)
md5old=$(cat /var/www/homeip.md5)
md5new=$(md5sum /var/www/homeip.log)

#echo "$(date) RunTime" &gt;&gt; /var/log/dyndns.log
if test "$md5old" = "$md5new"
then
        echo "$(date) - No change" &gt;&gt; /var/log/dyndns.log
else
        sed -i "s/^home.*/home IN A $newip/" /etc/bind/db.somedomain.com
        rndc reload somedomain.com
        md5sum /var/www/homeip.log &gt; /var/www/homeip.md5
        echo "$(date) - Updated ip $newip" &gt;&gt; /var/log/dyndns.log
fi</pre>
</li>
	<li>Create a cron job to run every few minutes. Run <strong>crontab -e</strong> and type
<pre class="lang:sh decode:true" title="Cron job">*/5 * * * * /scripts/dyndns.sh&lt;br&gt;</pre>
</li>
</ol>
<strong>How it works</strong>
<ol>
	<li>The router tries to access the specific web page on the web server that is located on the DNS server.</li>
	<li>Web server reads the IP from the router and if the hash is ok, it writes the IP into two files in the same folder
<ol>
	<li>One file for history purposes (with date and everything)</li>
	<li>One file with IP address only</li>
</ol>
</li>
	<li>Cron runs a script that calculates the MD5 hash from the file containing only the IP address and compares it to the MD5 hash from before the change. If the two are different - it updates the zone file by replacing the one record and saves the new hash to a file for future comparison (so we don't update and reload the zone all the time</li>
	<li>Zone is reloaded and propagated.</li>
</ol>