You’ll notice that all of the required ports are UDP which is a connectionless protocol and can’t easily be traced as there is no guarantee of delivery- the Mac VPN client just says ‘the server did not answer’. The manual mentions port forwarding, and also the built in VPN server in great detail, but does not mention that it can’t be turned off. So, let’s have a look at the documentation.
In theory it’s pretty easy (although even a big MSP managed to stuff this up causing me great frustration a few months back) you just have to forward the following ports for L2TP on Mac OS X I decided that the best option here would be to port forward the appropriate ports to the Mac server (which already has the usernames and passwords) so we could provide a reliable, easy to use and supported VPN solution. However the built in VPN server does not support the built in VPN software in the Mac OS, and you have to use something like VPN Tracker (up to $20 Aus per month) or IPSecuritas (free, but difficult to configure and support). This is a reasonably high end device (for Netgear) and actually contains the ability to terminate VPN endpoints. I’ve just spent a couple of weeks fighting with a very frustrating problem- setting up VPN passthrough on a Netgear DGND3700v2.
