How can I set up a second router for my roommate to improve his signal strength/coverage, and so that he is on a different subnet from mine?

Solution 1:

There are multiple ways to solve this problem.

If its possible to do so, the easiest way would be to get a second router. Move and reconfigure the current router to serve your flatmate. Connect the WAN port of your new router to the LAN port of his router over ethernet. Have separate SSID's for the 2 devices, and reconfigure your router to use a different subnet to his (ie if the current router uses 192.168.1.x use 10.0.0.x on yours). This will isolate your network from his (but not his network from yours, as your router becomes a client of his).

If this is not possible, you can reverse the above, ie keep your router as is, and connect the WAN port of a router for your Roommate to your routers LAN port. You again need separate SSID's and networks. In order to prevent your roommate accessing your router you will need to add a firewall rule ON YOUR ROOMATES ROUTER to prevent it routing traffic for your LAN onto yours (save for the common router IP)

An alternative to 2 routers with rules on the client router would be to have an ethernet router feeding each of 2 WIFI routers - even using standard NAT under this scenario will fix the ability to hop between networks. This is likely the "fairest" way of doing things, assuming you are each paying 50% for the resources. Also ethernet only routers are cheap. The disadvantage is both parties have double NAT. You will still need seperate SSID's

ALL OF THE ABOVE SOLUTIONS assume you can connect the 2 routers using ethernet (or look at Ethernet over powerline to link them)

Connecting the 2 connections over WIFI is harder and more wasteful -

A more expensive approach would be to use routers and bridges where 1 router supports multiple SSID's, and the SSID's can be configured to be independent. Ubiquity (no doubt among others) provides this - but this is harder to set up (you will need to understand about VLANS etc)

If you require fairly strong separation between the networks and don't want to become an expert in networking, you will want to have separate SSID's. Using prosumer/professional grade (again, Ubiquity can do this), you can have a single SSID and drop the customer into an appropriate VLAN network based on their credentials.