How to communicate with second network that also act as backup WAN

[cheetoz]

Hello. I have two networks with different subnet (please refer to drawing). First network is 192.168.1.0 and second network is 192.168.2.0. The OPN Sense act as DHCP server for first network and have two WAN. The second WAN act as backup if first WAN fail. The router in second network is Synology RT2600ac, also acting as DHCP server for second network. The IP address for OPN Sense's WAN 2 is assigned by Synology's DHCP using IP reservation.

My objective is to let PC 1 in first network to communicate with PC 2 in second network. Preferably the communication is one way, PC 1 can connect to PC 2 but not the other way round.

I tried the following settings in OPN Sense:

- Adding static route to 192.168.2.0/24 using Gateway: WAN2 (Backup WAN).
- Uncheck "Block private networks" and "Block bogon networks" in WAN2 interface setting.
- Allow traffic from WAN2 net to LAN net in Firewall Rule.

I also set static route in the Synology router: 192.168.1.0/24 using Gateway: 192.168.2.249 (OPN Sense's WAN2 ip on second network by DHCP IP reservation).

None of them worked. I am very green with OPN Sense, can someone please guide me how to set it up?

I've read about adding a third router with LAN port connected to 192.168.1.0 network and WAN port connected to 192.168.2.0 network and setting static route on both OPN Sense and Synology pointing to that third router. Will it work?

Thank you. Any feedback will be really appreciated.