Updated 06/17/2011: Before you get too far into this post I wanted to point out that I didn’t find a solution to getting a PPTP VPN connection to work with my AirPort Extreme Base Station. I switched over to using L2TP instead.
Updated: 08/03/2011: I’m moving to a different solution to bring PPTP back to my network setup, but you won’t like it. The step I’ve taken illustrates how inconvenient this problem can be.
Overall, I really like the new Airport Extreme Base Station that I purchased recently. The only problem I’ve had, and unfortunately it’s a major problem, is a loss of the ability to connect back into my network remotely over PPTP via Windows 7 (I prefer to connect to my VPN when staying in a hotel). I forwarded the appropriate ports but I was only able to use my network for about 20 seconds at a time. After that time was up I could no longer do anything on the network and the connection would usually close within a minute or two.
Unfortunately, I haven’t been able to find a true solution to this problem but I did find an acceptable work-around. I suspect this is a problem with the Extreme not properly passing the PPTP connection, though I don’t know for certain.
I started looking at using other VPN servers. Previously, I just had Windows 7 configured to accept VPN connections. I tried OpenVPN via a VMWare appliance in Fusion, but aside from configuration issues the larger problem was that I could not connect to the VPN using my iPhone or iPad.
My solution, which seems to have worked, was to purchase a copy of MacServe’s iVPN and move the VPN handling directly into OS X. Cost in USD was around $25. It hooks into existing OS X software but provides a simple GUI for management. This option turned out to be very easy to manage and works with all of my devices. Rather than using PPTP I moved over to L2TP.
On the Airport Extreme I setup three UDP ports to forward to a specific system within my network: 500, 1701, 4500
Currently, it sounds like OS X Lion may include similar capabilities, but I simply could not wait until the release of Lion.
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Hey, just read this and noticed you were talking about the PPTP passthrough issues through the router. I recently investigated PPTP passthrough to find exactly how it works and why it causes problems with routers. Take a look at it, you may find how to solve it yourself after reading it.