I bought a Planet VRT-311S router a while ago, and it took me some time to get the port mapping configured properly to make Azureus working properly.
The port mapping setting is not intuitive, there is no "port mapping" option in the admin manual. The "Virtual Server" option only has a few applications listed with no button to add new services.
I am writing this down in case I need to do this again. If anyone know an easier way, please let me know. This only works for fixed IP PCs on the lan.
The way to do it is through the "Firewall Rules" option. But first, you have to add the ports to the Security--Services option. Open the Security dropdown and select the Services option, enter the name such as "BT", select Type as "TCP/UDP", enter 6881 in both Start Port and Finish Port, click "Add".
Then go to the "Firewall Rules", select "WAN=>LAN", click "Add". Give a name like "BT", Source IP is "Any", Dest IP as "Single address", enter the client PC's internal IP (e.g. 192.168.0.10), Service is "BT (TCP/UDP:6881)", Action is "Forward" then click "Save".
Now, strangely, the "BT" service will appear in the "Virtual Servers" as "*BT", and correctly mapped to the designated PC.