This question seems to be similar to others, but I'll take a shot anyway. A client recently switched ISPs from TDS to Comcast Business Class. Before the switch, they had 5 static IP addresses assigned. Now they'll have a single dynamic IP address.
The issue is that this internet connection will be shared among two companies, both having (and wanting to keep) their own private subnets. Because TDS was supplying multiple IP addresses to the one location, this allowed me to put each router on the switch. Now, with Comcast, they only get one IP address, meaning there has to be a main router before the subnet routers. Luckily, the cable modem has a built-in router, which I would like to connect to each company's router, and still have DHCP enabled on all accounts.
Question: What do I need to do to the subnet routers to keep them separate from each other, but still allow internet access from the main router. I would love to say "I tried this", and give you links, but everything I find on the internet only mentions daisy-chaining routers with DCHP disabled.
Best Answer
The general idea is you have your cable modem getting its external IP from the ISP, and you create an internal network that accesses that. The primary router(your modem) gets the larger net, we'll use a big one for simplicity ...
Connect your modem/router to the subnet routers. If it's one of those SOHO things with multiple ports, those ought to work, if not you'll need a switch in between. Configure each router to be in the same subnet as the big one. to have a static IP in the subnet.
/16 and /24 are 255.255.0.0 and 255.255.255.0 respectively. You should also not use the IPs I gave, security through obscurity thing.