Using DynDNS with OVH

OVH provides rich features, one of which is a DynDNS service when you have registered a domain with them. In other words, if you have mydomain.net registered there, then you can dynamically register an external machine on a subdomain. In my example here, I will have my home PC registering as home.mydomain.net, which will allow me to access if from everywhere.

Configuring the OVH side

See this article on their knowledge base.

Configuring my home PC

We will be using a utility called updatedd, which seems unfortunately to be retired. You need to make some tweaks as per explained in this article. I am providing a mirror of the updatedd 2.6 source in case the repository provided in the article disappears : updatedd_2.6.tar.gz.

The article above proposes a cron script to regularly update the OVH server with the dynamic IP of the home PC, but I have found some issues with its logic on my side, so here is my version:

#!/bin/bash

## CONFIGURATION ##

# Connection to OVH DynHost
username=mydomain.net-home
password=SUPERSECRET
host=home.mydomain.net

# How to log
# 1 = true, 0 = false
log_change=1
log_no_change=0
log_file=/var/log/dynhost.log

# To avoid error "file not found"
touch ${log_file}

# Get Public IP
# FROM EXTERNAL WEBSITE
# ip=`wget http://www.monip.org -q -O - | grep "IP :" | awk -F' : ' '{print $2}' | awk -F'<br>' '{print $1}'`
# FROM LIVEBOX
ip=`wget http://192.168.1.1 -q -O - | grep '<td class="value">' | awk -F "[<>]" '(NR == 3) {print $3;}'`

# Get IP as defined in the DNS
ip_in_dns=`dig +short $host`

# Test if IPs are equal
if [ "${ip}" = "${ip_in_dns}" ]
then
	if [ "${log_no_change}" = "1" ]
	then
		echo `date +%Y%m%d-%H%M%S`: same IP in DNS \($ip\), so no need to push and change >> ${log_file}
	fi
else
	if [ "${log_change}" = "1" ]
	then
		echo "`date +%Y%m%d-%H%M%S`: IPs are different (DNS : ${ip_in_dns}, host : ${ip})" >> ${log_file}
		/usr/local/bin/updatedd ovh -- --ipv4 ${ip} ${username}:${password} ${host} >> ${log_file} 2>&1
	else
		/usr/local/bin/updatedd ovh -- --ipv4 ${ip} ${username}:${password} ${host} 
	fi
fi

Then just add this script to your crontab and you’re good to go.