Which username or password do I have to enter for VPN access?

For any authentication on the network (WLAN, VPN, 802.1X) your RPTU username followed by @rptu.de (in some cases still @rhrk.uni-kl.de) and your corresponding RPTU password is required. The former distinction between Unix/AIX/Linux password and Windows password is obsolete. If you have an older account and have not yet synchronized on the password change page passwort.uni-kl.de, you should do so as soon as possible. You can find out more about this under Account allocation.