Combining two networks

Question

I have two routers at home, each one is connected to a different modem.
So let's say, Router A is connected to Modem A, and Router B is connected to Modem B.

What I want to do is that I want all computers, no matter which router they're connected to, to be in the same network.

Meaning: If Computer A is connected to Router A, it uses Modem A for internet, BUT it has access to Computer B which is connected to Router B and is using Modem B for internet.

My question is: How should I conifg my routers ?

Answer 1

Sounds like a home-setup (ADSL for example?).

Of course there are several possibilities (with different security implications).

An easy way is: configure the routers as if they would serve the same network (but give them different IPs). You can check if it works by connecting everything to router A only (should work), then router B only (should also work, while all equipment gets IPs from the same network range).

In the final step you connect everything to one network. But before that, configure the DHCP-servers on the routers to hand out IPs from a different ranges. E.g. if the network is 192.168.10.*, tell one to hand out 192.168.10.20-40 and the other ....41-60.

Afterwards you might want to influence, which equipment prefers which router (they can’t easily use both!). If you don’t do this, then when the attached computers start, they ask for DHCP-served IPs. Both servers (in the routers) will offer one, and the computers will pick one or the other. As the offer includes the corresponding router as default gateway, this not-so-random choice of the computer decides which router it picks.

To solve this: you can manually configure IPs (and DNS?) on the equipment, e.g.: 192.168.10.61/24 with default gateway 192.168.10.2 or 192.168.10.1 (or whatever you gave router A/B).