I once tried to use the built-in Windows Server 2003 VPN features, using PPTP to tunnel in through the internet router.

This worked, but it had one important drawback: Only one person can dial into the VPN at a time. If you have two users who need to VPN into the local office, you'll need to use a different method.

Reason: PPTP VPN, when traversing NAT, encrypts the packets that tell it what the internal (nat-ed) addresses are. So you can get the router passing through the VPN packets just fine, but it can't tell the difference between one person's VPN connection and the next person's VPN connection.

So what happens is, you get this all working, one guy connects to the VPN and is working fine. Then the second guy tries dialing into the VPN and the first guy's connection mysteriously drops, but the second guy works fine for a while. Until the first guy tries re-dialing...

I gave up, said fuck it, replaced the cheapo router with a SonicWall TZ-170 with the client licenses for multiple VPN connections, and gave all the VPN users a disc to install the SonicWall VPN client software. Everything Just Worked after that. I could VPN as many simultaneous users as I'd paid client licenses for.

I think that I was asking for similar help on this BBS during that time. It would have been almost exactly two years ago. Perhaps some of the information in that thread would help. Anyone got a link to it?