These things have a couple of oddities worth watching for.
One of them is that adding a port-forwarding rule (“Virtual Server”) doesn’t automatically grant any access through the firewall, you have to add a separate firewall item to allow the traffic that you’ve just enabled.
The next thing is that saving to Flash doesn’t always work across the board, so do your saves, reset the modem, & test it. One place this bit me was that setting up port-forwarding rules, then firewalling rules, then saving the lot resulted in only the firewalling rules being saved.
The next thing is also port-forwarding: the forwarding won’t change the port, so a connection to 188.8.131.52:22 might be forwarded to 192.168.1.250 on the LAN, but always to port 22. So if you want to do my typical security trick of putting things like SSH services on odd ports, this has to be done on the machines themselves as well as adding a port-forwarding rule & a firewall rule to the ADSL router.
A final thing is that their PDF manual doesn’t quite match up with the real-life hardware. The differences are relatively minor, but they are there & need to be adjusted for.
Discovering all of this at a range of 4000 km was a bit testing, & I’m very glad that I had a patient, steady Jane as a relay between the ’phone & the keyboard at the other end, & that we use Southern Cross Telco as a telephone provider. They’re very steady providers, & have some useful long-term long-distance features to their plans, which allowed me to rattle on & experiment for nearly an hour across Australia for less than a gold coin.