How to connect internet modem/router combo to a router, but keep it working as a network switch?

Question

Okay, so I want to buy a new router and want to connect my home network like this

My question is, will this work? I am not sure if I connect Modem/router to WAN port on main router I'll be able to reach computers connected to modem from computers connected to main router. If yes I guess QoS will apply for intra-net connections between floors that way, is that correct? Can I avoid this somehow without having to connect the floors with another cable?

Are there any other limitations I should be aware? Would you recommend to change something? I have some spare oldrouters/switches I could use, but I want to try to avoid using them if possible.

Answer 1

Disable DHCP on the "Main Router" and connect a line from a switch port from router in floor 1 to switch port of router in floor 2 (do not connect the line to the WAN port of the "Main Router"). Set the IP address of the "Main Router" to an acceptable address range for the subnet mask as set for the router on floor 1 (but outside the DHCP range) so that you can still access the settings of both routers from any computer. You will not be able to connect the two routers together wirelessly unless the "Main Router" has the ability to be a client instead of an AP. There are only a few routers that I have seen that allow for this, so most likely you will need to physically attach the two routers with a network cable.

Answer 2

Assuming your internet connection is floor 1, I'd disable DHCP service in "main router" and only use it's switch ports. I'd turn off it's wifi unless the floor2 wifi-only devices can't connect to the floor 1 router.

Actually I'd buy a small gigabit switch, they're cheap, more efficient and less likely to cause confusing configuration problems.