I'm sorry to bother people about this again. What I thought was a solution to an earlier problem turns out not to have been a permanent one.
I wanted to open some ports in the above modem, but couldn't access the modem's internal web server using Firefox for Linux. I was, however, able to do so using Internet Explorer (on my dual-boot computer) and to create an appropriate NAT rule. Then, when I restarted the computer and booted into Linux, the rule I'd created in Windows persisted in Linux.
However, when I later powered the computer (and modem) down and then powered up again, the rule I'd created was gone.
Although not exactly a solution to the problem you're having with the CLI, did you remember to save & reboot or at least save after you'd entered the NAT rule? Thats been my downfall _many_ a time. -- Cameron