I have a situation where I need 2 LANs to use the same ISP Gateway and ISP IP, but the LANs cannot be able to interact with each other. I am guessing I need two DHCP servers at the same scope. I have already tried having a DCHP server under the other DHCP server scope (but with a static IP) and setting up the nested DHCP server to use the upper DHCP server as the gateway and I could access the internet, except any device on the nested DHCP could interact with the entire LAN.
Since I can't just hook up 2 DHCP's to the modem and share the same ISP IP and ISP Gateway, do I need to have a router setup up as a gateway (by this I mean just take create a LAN, will turn off any DHCP and statically assign IPs) that which will use the ISP IP and Gateway, then have 2 DHCP's connected to that router and point them at the router for the gateway to the outside internet? If I do this, will one device on a DHCP not be able to see interact with a device on the other DHCP? Also, if I do this will I be able to setup a virtual server 'chain' so I could remotely SSH into a device under one of the DHCP's?
Is there any way I could do this with an linux based router firmware with a single router rather than 3? I'd prefer to do it in wrt if at all possible, but I wonder if I could do this in IPFire?