Pi as VPN gateway/router for a subnet

[fiendish_foe]

I'm using a fresh raspbian stretch SD card.

Sorry if I can't get my meaning across well, I'm new to this and still learning.

I'm trying to set up my Pi as a sort of VPN gateway/router. I'd love to know which of the two would be a more apt description. Ultimately devices connected to the pi through eth1 (USB) should be able to access both the internet and the VPN connection.

The pi is connected to a local network through eth0 (ip 10.10.0.126, netmask 255.255.255.0) and gets it's address from a DHCP server . Eth0 is the connection to the interent.

The pi builds a connection to the SSL VPN server using openfortivpn (using PPP). Works like a charm. I'll worry about VPN later, right now I'm stuck at networking.

I would like to create a subnet on eth1 (via USB). I'm trying to wrap my head around dhcpcd.conf and the potential need to set up isc-dhcpd-server to create a subnet, but honestly I'm at a loss. Any help would be appreciated.

[topguy]

Setting a static IP ( for example 192.168.32.1 ) on eth1 is the first step.
(If all the other devices on that sub-net also can be set to static IP then you dont really need DHCP. )

All the guides I have seen related to setting up the Pi as a router or wifi AP uses "dnsmasq" so I think you will find a lot of information about that program if you search.

The same guides should also contain a lot of information about setting up forwarding/NAT/routing between different intefaces etc.