Hi,
I tried to follow the guide
http://www.howtoforge.com/linux_rdiff_backup , but that did not work for me because I have a static IP and to get it work as the guide I need to change every time the reverse lookup of my IP.
I found a solution with dyndns.org (now
http://dyn.com/dns/). They still offer a free dns, just one but if you cancel the trail within the 14 days it remains free as a bonus for testing it.
My setup is different, because the server initiates the backup.
Have a look at
http://vecks.com.br/rdiff-backup-com-ssh/. It is in Portuguese, but following the instructions should be no problem. Suggestions are welcome.