Our estate has a load management system for the electric car charging stations. This is required by law. The controller of the charging stations offers an API and runs in a LAN without Internet access (which is explicitly intended). A LAN cable goes to the wallbox in each house. I also have a LAN and a Mikrotik router in my house. I would like to access this API from my LAN. I can plug the LAN cable from the wallbox into a brigde or into my router.
How do I connect the two LANs so that I can access the controller API, but it cannot access the Internet and other devices from the controller LAN cannot access my LAN?
Use dedicated subnet for charging network on your router (e.g. remove one port from bridge, connect charging LAN to that port, add IP setup to that port). Then configure really restrictive firewall to/from charging network with few wanted exceptions. You may need to add SRC-NAT for connections towards charging network as it’s quute probable that devices in that network won’t use your router as any kind of gateway (not even towards your household LAN).