I've previously set up OpenVPN servers without much difficulty but I'm having trouble wading through the documentation of other VPN solutions.
So, my question is: can I configure openl2tp such that any Windows clients who connect are given addresses which are part of the LAN pool and therefore are completely transparently connected to the LAN?
This is how Windows Server does it and would remove any requirements for NAT or routing for the rest of the LAN. It's apparently not possible with Poptop, but I can't ascertain whether or not it's possible with openl2tp or anything else.
Sorry for my late reply. I'm not sure I understand your question.
The OpenL2TP server can assign the PPP client IP addresses from a pool.
If you are asking for those IP addresses to be assigned from a DHCP server, that would require some pppd scripts at the server to invoke a DHCP client. I've never tried it.
If you want the client to be bridged to the server's LAN, that requires PPP bridge protocol (BCP) which is not supported by Linux.