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The DynDns


  • Ip address
On the internet, computers communicate using the TCP/IP protocol, which identifies each machine, each computer in the form of an address:
  • DNS
The computers communicate with each other through the IP, but to make things easier for humans, these IPs are translated into computer names (and viceversa) so that they are easy to remember: this translation is done by the DNS servers.

What is a DynHOST used for?

If you use an ISP with ADSL or RTC connection, your IP of connection change at each re-connection.
DynHOST allows you to point your domain or sub-domain to an IP of connection and, if it changes, to update it in real time. In this way, you can host a website on your ADSL line. If you play on line, you can directly communicate your domain name instead of an IP difficult to remember.

Creation of a DynHOST

You just have to request for a DynHOST via the Manager.

  • Access to sections’ section
  • Domains & DNS’ button
  • then ‘DNS Zone
  • DynHOST type

Once on this page, add a DynHOST in DNS Zone:

Indicate a sub-domain and a ‘DynHOST’ (IP address)
The creation of this field takes 24 hours

Warning: Your domain must have the following DNS (or hosts using the IP of the following DNS):

  • Primary DNS:
  • Secondary DNS:

If you would like to host pages on your machine, you must obviously have Apache on your machine.

DynHOST identifiers

These identifiers enable you to update the IP of the DynHOST using a software external to OVH (see below).

An identifier enables to manage one or all DynHOST sub-domain(s) that you have created. It is made of the domain, followed by the name you want, i.e.:

At the time of the addition of a new DynHOST, an option to tick allows you to create an identifier directly after validation of the creation.

You can manage them via the Manager.

  • Access to sections’ section
  • Domains & DNS’ button
  • then ‘DNS Zone
  • DynHOST Identifiers

Once on this page, you will be able to manage your identifiers (creation, modification, password and deletion)

Tools to use

Next, you just have to download a software of IP management:

Microsoft/Windows software

GNU/Linux Software

For this script, try to replace the variable my$server_name=””; by
(Do not take into account the possible error in return)

For this script, look for the following section:
Updatehost = “”
Updatepage = “/nic/update”
Useragent = “ipcheck/” + Version

And replace Updatedhost = “” by
Then, you will just have to set this software with your DynHost? identifier and its password.

Examples of use

  • Bali ‘DynDNS’ (Windows)

Set this small software with your DynHOST identifier and its password.
Main section
user/pass: DynHOST identifier & password
update your IP for these hosts: (DynHOST field that you have created from your manager)

For further information: Consult faq section of the software

  • ‘Direct Update’ (Windows)

Untick “Desactivated/ignore this account
DNS service: Select
Detection of IP: select ‘Detection of IP by default”
User name: your DynHOST identifier
Password: the password associated to your Identifier
Domain/host: the sub-domain for which you have defined a field of “DynHOST” type in the Manager.

  • (Linux)

What do you need to have?

  • The following archive: DynHost.tgz
  • A python translator
  • An internet connection working under Linux ;)

Installation of scripts:

The archive contains the following files:

  • the script in python, that up dates your DynHOST field at OVH,
  • dynhost: a bash script that checks that your public address has been modified and calls the script shown above with the correct settings,
  • old.ip: a text file that contains your previous public IP address.

Unzip the archive in the directory of your choice and edit the dynhost file to include your settings:

IFACE= ppp0
LOGIN= test-ovh

  • IFACE: the network interface on which your internet connection is activated
  • HOST: DynHOST field that you have created from your Manager for your domain name,
  • LOGIN: your DynHOST identifier,
  • PASSWORD: The password associated to the Identifier,
  • OPTIONS: The different options possible in script (empty by default, see lower)

Check as well that the dynhost script has the right authorizations of execution for your user. Any operation carried out by the script are saved in a dynhost.log file.


  • To update the DynHOST field for your station

It is in case of traditional use. Your computer uses Linux, it manages the connection and is connected to an Apache server. You just have to execute the dynhost script. This one recovers the IP address of the network interface used by the internet connection (ppp0 by default), then it compares it with the address previously updated (stored in the old.ip file). If the address has been correctly modified, it calls the script to update your DynHOST field with this address,

  • To update the DynHOST field for another station.

The use is the same one as above. However, the dynhost script does not recover the IP address but uses the one you specified. To do so, you just have to specify ‘-a10.0.0.10’ option in OPTIONS section where represents the IP address with the one your DynHOST field must be updated. It is a static IP, this method is not appropriate if your ISP provides a dynamic IP.

  • To update the DynHOST field for a router (tested with Linksys WRT54G)

It is in case you use a personal router behind which you have a WEB server. The script allows you to update the DynHOST field with public IP address of the router. This is possible if your router provides a WEB interface of administration. To do so, you have to specify the option “-rhttp:/” in OPTIONS section. is the address used to obtain WEB interface and Status.php is the page on which is the public IP address of the router.

Warning: It does not regulate the configuration of the specific Fowarding Port proper to each router! With this option, the script will request from you to enter the password necessary to access to the WEB interface.

Installation in crontab for periodical execution

This handling enables you to indicate to your system that it must restart periodically the dynhost script. In that way, your DynHOST field has more probability of being up to date if your ISP regularly forces you to change the IP address.

The frequency on which the script is executed depends on your use, you may set it up to be executed once a day, every hour…..

The content of the crontab change by executing the following command:

This file edit itself in the same way as a Vi editor (key i to insert, -ESC- then :wq to save and quit).

Add one of the following lines in the file, according to your needs:
101**/home/user/dynHost/dynhost (every 1st of the month at 00:01)
10**0 /home/user/dynHost/dynhost (every Sunday at 00:01)
10*** /home/user/dynHost/dynhost (every day at 00:01)
1**** /home/user/dynHost/dynhost (every hour)

/home/user/dynHost/dynhost represents obviously the complete way to the dynhost script.

You can check the content of your crontab by executing this command:

Bash-2.05b$ crontab -1

More info about crontab here

Tips if you have many DynHost

If you have several DynHost fields on different domains, the update of all these fields can quickly become very complicated, if the most of the fields that you have point to the same Ip address, you can make the task easier for you by using CNAME instead of DynHost.

A CNAME allows to redirect a field to another address. For example, you have 3 domains:, and

these 3 domains have a DynHost called forum:

They all point to the same Ip

At each modification of this Ip address, you must update these 3 fields.

By using a CNAME, only one field will have to be updated (the one of your choice).

You must keep one DynHost field, here we choose to keep, the others can be modified in CNAME.

To sum up: becomes a CNAME of becomes a CNAME of

Once is updated, and are automatically updated.

Finally, you will have:, which is a DynHost to your Ip address, which is a CNAME to, which is a CNAME to