I had the same topic once, but the solution is not working now...
I have dovado router with LTE usb stick bridged. IP from ISP is assigned directly to ether1 on MT. I have added another IP address manually to ether1 which is 192.168.0.2 to be able to communicate to dovado which is 192.168.0.1. Unfortunately MT doesn't see dovado. What's wrong?
On the other hand, I have another MT router, where EPON terminal (192.168.1.1) is connected to, and after adding 192.168.1.2 to MT they started to talk without adding any special rules to firewall.