Dynamic DNS: Publishing our domain

Usually we have not fixed IP in our home connection, it have a cost and the bucget is little (null).

The target is to warn to a DNS server when our Internet Service Provider (ISP) changes our IP direction, to reply new IP in following queries.

To do this, publish our domain, usually will be dirrected through a Dinamic DNS Service as provided by www.dyndns.org company.

There are two ways to make the synchronization:

  • Through the router: the router notifies the service (p.e. dyndns.org) all the IP changes. It is the most reliable, since it notify inmediately the changes. Firmware router must have this option.
  • With an schedule task: your machine test your public IP witha a fixed frequency, and if it changes, it notifies to the server. This method can prompt a time without service, between the change and the next test. The least reliable (routers without this option).

I used theese two services:

  • freedns.afraid.org: I recommend it, much posibilities to work, as controlling subdomains. FreeBSD service implemanted (=high reliability).
  • www.dyndns.org: The most famous company for this purpose. Usually the routers sinchronize with it. The problem: if router sends many sinchronization messages, they cancel your account, levin you web without visibility (it suceed many times).

Router synchronization

We create a DYNDNS account (http://www.dyndns.com):

  • User / Password: my_nick / securepassword
  • We create a free domain (i.e.: tmos.dyndns.org).
  • Create a Dynamic Host:


  • The domain tmos.dyndns.org pont ro the figure IP, until your notification (the router notifies in this case).
  • You can see your actual IP in the web: http://whatsmyip.org/.

Nowadays routers have a synchronization option with some Dynamic DNS services.

In may case Comtrend 536+ is the router, it we must configure as follows:


Then, when IP changes, it notifies to dyndns.org. This way when a DNS server ask for the direction tmos.dyndns.org, dyndns.org’s servers reply with our new IP notified by the router.

Therefore my direction must ponit to my home webserver: http://tmos.dyndns.org.

The routers Linksys WRT54G can synchronize with freedns.afraid.org, that I recomend better then dyndns.org.

Synchronize with a Script in the crontable

Go to the solution in the following link: http://foertsch.name/DynDNS/ here you can download a shell script wich points the IP number in a file.

It has to be configured, and to be scheduled in the file /etc/crontab to run every 5 minutes.

You can find other ideas, or for non-unix systems in the following link: http://freedns.afraid.org/scripts/freedns.clients.php

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