THE SOLUTION FOR SPEEDTOUCH ROUTERS

Most modern routers use NAPT instead of NAT for port-forwarding.
JJ2 requires pure NAT. Therefore the setting using the webinterface just does not work.
The explanation + instructions can be found here:
http://forums.ac.turbine.com/showthr...t=30616&page=2

Basicallly you need the command-line interface (CLI) to instruct your router.
We have a Speedtouch 780:
after logging in as described on the linked page
--nat config trace=enabled
then
--nat mapadd

it will then ask you for a few settings. I used the following settings:

--intf Internet
--type nat
--outside_addr your routers internet adress (see http://whatismyip.com)
--inside_addr (your computers home networkIP address - e.g. 192.168.1.64)
--access_list
--foreign_addr
--protocol udp (or leave blank)
--outside_port 10052-10054
--inside_port 10052-10054
--mode (also leave blank)

If you do not get an error or failure and your prompt returns, then;
--saveall
--exit
instructions for our router are e.g. in
http://www.speedtouch.nl/docs/ST706W...L_CLIguide.pdf

And then finally finally it worked.
Hooray!