Installation of the mobile configuration
Please download the mobile configuration profile (vpn-uni-tuebingen-2021_iOS.mobileconfig) from https://uni-tuebingen.de/de/2178. Always use Safari on iPadOS or iOS, the download may fail with other browsers. (see at the end of the page, there is also a direct link to the configuration profile)
You'll get a message: "This Website ist trying to download a configuration profile. Do you wand to allow this?"
Tap "Allow".
A message saying "Profile downloaded" will appear. Tap on "Close".
Now switch over to Settings › General › Profiles (iOS 15: VPN and Device Management)
Tap on the "VPN" profile under "Downloaded Profiles". Tap "Install".
Enter your passcode for your iPhone/iPad. Tap "Done"
You'll get a warning about security risks of this profile. Tap on "Install". A message will pop up, confirm with tapping on "Install"
Enter your ZDV LoginID. Tap on "Next". On the next screen, enter your corresponding password. Tap on "Next".
Tap on "done". The profile is now installed.
You can now start and stop the VPN conncection from your Settings › VPN.
This profile forces all network traffic through the VPN connection. it might be necessary to first disable the vpn-connection before you can use local services in your network (for example: printing on a local airprint-printer or access files on a NAS)
Check the vpn-connection
sometimes it is important to check if the vpn-connection was successfully set up.
Visit https://whatismyip.com/ and check if you get an IPv4 address in the 134.2.x.x range and your ISP is the University of Tübingen. This means that your connection was successful.
Anything else shows that the vpn-connection is not correctly set up or your device is not using the vpn-connection. Unfortunately, iOS/iPadOS does not allow to change any settings here, so removing and reinstalling your configuration is the only option.
Sometimes, the reason for your failing connection is to be found on your local network. Please check if your router has VPN-Passthrough activated, also you night need the help from your ISP. You should make your ISP aware that you need an L2TP connection.
Remove the vpn / configuration profile
To remove the vpn, go to Settings › General › Profiles (in iOS 15: "VPN and Device Management"), tap on the vpn profile, then tap on "remove profile".