This custom cable modem my ISP gave to me does not support forwarding an external port to a different internal port. (For example, I can't forward an incoming connection on port 80 to port 3389 on my main box and and an incoming connection on port 21 to port 3389 on my old box. I need to do this to avoid port blocking.)
I know I could go around this by changing the port of RDP on my machines but I can't because I already have an HTTP server which must run on 80 for internal testing purposes.
I could not find any software updates, I could not get any support from my ISP and I could not find any better cable modems. (Cable modems are very uncommmon compared to ADSL modems.)
So is there any way I can go around this limitation?