Hi Gabriel,
After long trial and error I went now a different way, maybe as an alternative to your solution.
As mentioned before I did not want to drill a hole in my router (fritzbox).
On the other end I wanted to use the webhook of Geofency as “post - method”.
Thus I was looking for a way to use VPN automatically to connect to my OpenHab server.
What I found was this:
http://www.meintechblog.de/2015/02/vpn-on-demand-zwischen-iphone-und-fritzbox-einrichten/
This link provides a very extensive a solid description on how to accomplish a VPN-on-demand connection to the server; client is an iphone.
Using this method, the Geofency app (which is really a fantastic presence locator and much more) will automatically set up a VPN connection when I leave a location and execute a php script on my server changing my status from “Anwesend” to “Abwesend” or “Arbeit” or what ever locations you have defined.
Note: I cannot determine any increase in power consumption or of battery life of my iphone.
Cheers
Björn