Remote Desktop fails with Router

[MacPeople]

Using Apple Remote Desktop 3.2 and a Speedtouch 330 USB broadband modem I used to be able to connect to my parents' machine and fix problems via the Internet. Since upgrading to a Speedtouch ST585 ROUTER, I can only share the other machines desktop; I can no longer perform reports, transfer files, etc. I also can't upgrade client software - it says "This task will fail: The Remote Desktop Client software is not active on <client machine>" - when it IS! It all works fine if I just plug the old modem back. I suspect it's an issue to do with a router's firewall or port forwarding but have no idea what I need to change on MY machine to make it work. (I managed to switch OFF the firewall but it make no difference.) Can anyone advise what setting I need to change (and how?). Thank you. (http://speedtouch.lan/ gets me to the router's menus but I don't know where to go from there.)

[Giaguara]

Make sure UDP port 3283 port is open on your router. + other ARD ports.

[Satcomer]

On a Mac you should always keep the Apple knowledge article "Well Known" TCP and UDP ports used by Apple software products bookmarked.

Plus if you buy a router make sure you check that router's manual/web page handy. Each router manufacture have different ways of opening/closing logical ports.