We use a Windows 2008 R2 box for our LAN DHCP. I have just replaced our router with a Draytek 2820n and have set it up for PPTP VPN (with Radius authentication).

I do not want to enable DHCP on the router because I don't want it handing out DHCP to the clients on the LAN.

Also DHCP relay on the router does NOT work for VPN according to Draytek customer support here in the US, so that won't work.

The only thing that has semi-worked is "IP address assignment for dialin users (when dhcp disable set)". That hands out IP addresses to the VPN clients, but doesn't assign them DNS servers.

HOW can I get DHCP for the VPN clients without moving DHCP for the entire network to the Draytek? (Not only would that be inconvenient, it's also not an option as it doesn't appear to support the sort of DHCP options we need for our VoIP phone system).

as a temporary bandaid until i can get an answer, i set the WAN primary DNS address to the internal DNS server. the WAN DNS servers are what get assigned to the VPN clients.

this will slow down non-cached external name resolution for LAN clients, but it will buy a little extra time to get a better answer