Hello,
I am not able to grasp all the information you mentioned but from what I understand you have a DSL router that is having a public IP address? And you want to do port-forwarding? Could you clarify or draw a sketch of what are you trying to achieve it is best to include the IP address details if it's public IP you can put X.X for the 3rd and 4th octet.
Looking forward to getting this data from your side.
Regards,
Jerome