It would seem to me the part you are missing is the port forwarding on the Belkin Router of port 8080 to 192.168.2.21. You should set that to a static IP if it is possible.
Let me know if you need a more detailed explanation. I just purchased the SDE-120 and probably won't have time to set it up until this weekend but from a networking perspective, I believe that is the piece you are missing.