Port Forwarding with router and airport

[Justmeandmymac]

I am not able to forward a port correctly with my current set-up.
I have a belkin router connected to the internet and airport (BS) as wireless router set-up as bridge mode, connected to the belkin via a cable. I can see that my mac has the IP xxx.3, my router the IP xxx.1 and the airport base station the IP xxx.4.
I have tried to set up the port forwarding on my router to point to xxx.3 as well as xxx.4 but nothing works. I have also allowed the program on my mac to receive incoming connections in the firewall setting on my mac.

any suggestions ... ? Please.

 

[Justmeandmymac]

Solution

The first router is set up to forward the port to the Mac's IP while the second one has the router functionality disabled (bridge mode).

After surfing and reading I do not know how many posts, I thought about not trusting the Mac OS firewall and I changed the setting from "essential services with added transmission for incoming connections" to allow specific services (and managed them when they come up). And indeed after starting transmission I have got the request if I would like to allow this application to receive incoming data which I accepted ... result: port is open in transmission. Well I guess that there is something not really working as it should in the firewall ....