Using internal DHCPv6 for internal machines and Global for WAN connection

Greetings,

I am trying to use my internal DHCPv6 server to serve FDC8/64 subnet addresses to my internal machines and only take the Comcast Gloabl IPv6 Address for the WAN interface on my router.  It would look something like this:

Global-->Router-->FDC8::1 (internal LAN Router address) -- DHCPv6 Server for FDC8 Subnet--> Client Machine FDC8::2, etc.

I using a DLink DSR-250 as my Router and Windows Server 2012 R2 for my DHCP server, I just don't know what flags to set to make this  happen (PD, M, O)

Any suggestions?

Bob Hessenauer