I've set up a home network with two routers (TEW-692GR and another one from TP-LINK), but neither supports on-site VPN server configuration. I stuffed my RPi with Raspbian into the box with my router and turned it into a PPTP server, however I found it impossible for external computers (VPN clients) to obtain a local IP in my subnetwork (192.168.56.XXX). In the PPTPD config files I found that it is only possible when the device (RPi in my case) distributes IP addresses, so I decided I would turn it into a DHCP server for my router and disable DHCP capabilities on my main router.
The main question is, how is it possible to turn RPi into a DHCP server with WAN running through my primary router and RPi connected to the LAN port of that router? I'm not really into turning my RPi into a WiFi access point, since the dongle I'd be using sacrifices overall network performance.