Allow communication between two networks

Question

+--------------------------+                   +--------------------------+
|  Office A                |                   |  Office B                |
| Technicolor TG784n v3    |                   | (router model not known  |
| 192.168.1.1 (router)     |                   | 192.168.5.257 (router)   |
| 86.3.12.12 (external ip) |  <- powerline ->  | 82.1.9.79 (external ip)  |
|                          |                   |                          |
| DHCP Server:             |                   | DHCP Server:             |
| 192.168.1.*              |                   | 192.168.5.*              |
| Mask: 255.255.255.0      |                   | Mask: 255.255.255.0      |
+--------------------------+                   +--------------------------+

I have two distinct spaces, each with it's own router and internet connection. I would like to keep everything as-is but allow computers from 192.168.1.x to be able to talk with computers from network 192.168.5.x.

On top of that both DHCP servers should keep serving each network as they previously were. A new computer that connects to Office B should get the IP 192.168.5.x and access the Internet via the external IP 82.1.9.79.

Is this possible?

(the powerline works as an ethernet cable)

Many thanks.

Answer 1

With the right devices, this will be easy. Just connect both routers to the powerline and tell them to send traffic to the other network via the interface connected to the powerline (this is called setting a route). If and how this is possible with your specific devices we can't tell.

What happens then is that every computer in Office A knows from the DHCP server that it should send all traffic not destined to the local network 192.168.1.0/24 to the standard gateway 192.168.1.1 and it's the routers job to make sure the packets take the correct route (to the WAN interface for most traffic and via powerline for the 192.168.5.0/24 traffic.

And vice versa for Office B, obviously.