I need your help in setting up routing in a somewhat complex network. Let me give you the facts first (the question is way at the bottom):
The installation has two physically separated networks, internal (192.168.0.0/24) and external (192.168.1.0/24).
On the external LAN there's a DD-WRT router (192.168.1.1) with OpenVPN installed, responsible for the Internet-connection. The OpenVPN network is 10.8.0.0/24, with the router having 10.8.0.1.
There is also a Windows 2008 R2 server with two NICs, connected to the external LAN on 192.168.1.7 and to the internal LAN on 192.168.0.7.
Additional user PCs are on the internal network, i.e. in the 192.168.0.0/24 subnet (e.g. PCSales on 192.168.0.150). They have no Internet connection, and are not supposed to be able to access the Internet. (As a general measure, their default gateway points to the Windows server on 192.168.0.7.)
I have some remote OpenVPN client that connects to the router's VPN, receives the VPN IP 10.8.0.6 and can ping the router (on 10.8.0.1) and connect to the server on 192.168.1.7 without problems - that's a standard setup I'm quite familiar with. (The PC received the pushed route 192.168.1.0/24 via 10.8.0.5.)
Now here's the problem: I would like to access the PCs on the internal network from my remote PC for maintenance purposes. How do I have to configure the system so that the remote PC can not only talk to the PCs on the external LAN but also to those on the internal? I expect that I need some combination of static routes on the internal PCs as well as configuration of the RRAS service on the Windows servser.
Thanks a lot for any _qualified_ advice. (Please do not reply if you are only guessing yourself.)