Track IP Address using DD-WRT + CRON + WGET

After moving to my new apartment, it was time to dust off the old Linksys router I had lying around. This thing has been hacked to run the latest DD-WRT that it could handle.

My network address changes occasionally, and I didn't want to setup any dyndns accounts to keep track of the IP and have it resolve to a hostname. Honestly, just being able to get the last IP address is good enough for me.

So, I came up with this script that I run on one of my websites which listens for HTTP requests. When it gets one, it simply logs the IP to a file and spits it back out to the client.

Then, whenever I want to grab the IP address of the home network, I just hit another URL to grab the IP. The script is requested from my router every hour.

Configuration

Open your DD-WRT settings, go to Administration | Management, and scroll down till you see the section on CRON. You can add the following rule to have your router grab the file every hour:

*/60 * * * * root wget http://example.com/ping.php

ping.php

<?php
$ip = $_SERVER['REMOTE_ADDR'];
$handle = fopen("./ip.txt", 'w');
fwrite($handle, $ip);
fclose($handle);
echo $ip;

pong.php

<?php
echo file_get_contents("ip.txt");

Setup

touch ip.txt
chmod a+w ip.txt

Obtaining IP

Simply browse to http://example.com/pong.php to get the last known IP address.

Thomas has contributed to dozens of enterprise Node.js services and has worked for a company dedicated to securing Node.js. He has spoken at several conferences on Node.js and JavaScript and is an O'Reilly published author.