I run a vpn server on my home router that I use on sites that limit certain types of connections (ranging from smtp, ssh to bittorent, lots of networks permit just http and https traffic). When I am at home, my laptop gets address like 192.168.10.10 on wlan0 interface and when I connect from outside I get 192.168.20.20 on tap0 interface. I forward one port (say 55555) to 192.168.10.10 and other (say 54444) to 192.168.20.20. This means that I need to manually change ports I use in the client everytime I switch from vpn to home connection or viceversa.
It would be nice if transmission were able to change ports dynamically based on an IP address or on interface (wlan0 or tap0 in my case). Or is it already possible? I could not find it.