OvhDnsup - Dynamic DNS for IPv6

This software enables you to safely update DNS zone entries hosted by OVH. As of January 2021, OVH does not allow dynamic DNS (DynDNS) updates for IPv6 addresses when using their DynHost protocol. This software provides a work-around for this limitation by using the OVH API to perform this task. Security is ensured by generating a DNS-entry-specific access token, which can only be used to update the corresponding entry. Hence, if this token is stolen the possible damage is limited.

This client also supports IPv4, however, in this case you probably want to use OVH's DynHost feature.

Either clone or download this repository and execute (after installing Bundler):

$ bundle install

Or install it yourself by running:

$ gem install ovh_dnsup

You might want to add the --user-install flag to install into your home directory.

This section describes how to setup OvhDnsup to dynamically update a domain. We shall use dynamic.example.com as an example. You have to replace the domain example.com and the hostname dynamic according to your needs.

First, you need to register the application with the OVH API. Enter

$ ovh_dnsup register

(without the dollar sign) into a console, which will start the registration process. Follow the instructions on the screen.

Next, you need to login:

$ ovh_dnsup login

Again, follow the instructions. This login will request access to a few API functions, which are needed for the management of the dynamic hosts. We can, however, later drop these privileges to ensure security.

Now, you have to request the an authorization token for the domain update. Note, the A and/or AAAA record need to be created first in the OVH customer center! When the subdomain is created, execute:

$ ovh_dnsup authorize example.com dynamic dynamic_example_com.token

After following the instructions on the screen, you have created a file dynamic_example_com.token which contains the authorization information to update the hostname. The file is restricted to updating only the hostname you have authorized. Note, you can inspect and manage all authorizations using the ovh_dnsup sessions command. Furthermore, make sure to grant access for the time period that you want to perform updates in.

Updating the IP address can be done essentially in two ways. You can set the IP address manually by executing:

$ ovh_dnsup update --ip 2001:db8::abcd dynamic_example_com.token

You can also use an interface name to update the IP address:

$ ovh_dnsup update --if eth0 --daemon dynamic_example_com.token

The --daemon option instructs OvhDnsup to periodically check if the IP of the interface has changed and in this case to update the hostname.

When you have convinced yourself that your setup is working, you can run the command

$ ovh_dnsup logout

to log out from the management interface. From now on, only DNS updates are possible using the corresponding token files. (You can, of course, re-login at any time.)

In general, you use OvhDnsup by executing:

$ ovh_dnsup command [arguments...]

The following commands are possible

For more information on the individual commands run:

$ ovh_dnsup command --help

The following commands need to be executed as root. First, create a service user.

useradd --system ovh_dnsup

Then, save the token file as /etc/ovh_dnsup.token and execute

$ chown ovh_dnsup /etc/ovh_dnsup.token
$ chmod 700 /etc/ovh_dnsup.token

to set the right permissions. Afterwards, create a service file:

$ cat > /etc/systemd/system/ovh_dnsup.service << EOF
[Unit]
Description=Update OVH DNS

[Service]
User=ovh_dnsup
Group=nogroup
ExecStart=sh -c '/usr/local/bin/ovh_dnsup update \$(cat /etc/ovh_dnsup.conf) --daemon /etc/ovh_dnsup.token'

[Install]
WantedBy=multi-user.target
EOF

Set you configuration by executing

$ echo "--if=eth0" > /etc/ovh_dnsup.conf

where you replace the eth0 by the interface of your choice.

You can now start and enable the service by

systemctl start ovh_dnsup.service
systemctl enable ovh_dnsup.service

After checking out the repo, run bin/setup to install dependencies. You can also run bin/console for an interactive prompt that will allow you to experiment.

Bug reports and pull requests are welcome on GitHub at https://github.com/hrittich/ovh_dnsup.