Is it possible to port forward from a BR1 that is maintaining the WAN connection to another router sitting behind the BR1 that also has firewall rules being enforced? The second router is a MikroTik routerboard.
This can be configured in the BR1 under: Advanced> Port Forwarding.
I know of typical port forwarding. However, I believe there needs to be some other specific programming required for this case. Router 1 connected to the WAN is the BR1. There is then another router behind the BR1, which is the MikroTik Routerboard, for a second LAN that is also running firewall rules. Simple port forwarding on the BR1 is not working.
You also have to configure the firewall to allow the traffic. The port forwarder will try to forward it to the device, but the firewall will drop it if configured to do so. Did you make a firewall rule for
Source - Any
Destination - IP of device being forwarded to
Select the wan links that traffic will come from
Hope this helps