I've had the DLink 4100 for some time, and it's always worked fine (DHCP mode). It also handles access to a web cam. My setup was something like:
ISP <-----> 4100 <--------> switch <-------> various computers and devices
| (LAN Port)
WebCam (as virtual server)(uses port forwarding 7500/80)
I just changed ISP's and I'm now on DSL. Initially, I just connected the DSL modem (Westell G90-610018-20 ADSL Modem) to the WAN port of the 4100. The DSL modem connected by PPPoE, and I left the 4100 in DHCP mode. I had no problems accessing the internet, but the internet could not "see" my web cam; and various tests showed that the port was blocked.
I then put the DSL modem into "bridge mode"; changed the 4100 setting to PPPoE (and changed nothing else other than entering a user name/password for the PPPoE logon). After this both internet access, and also behavior of my webcam, were both OK.
The only problem is that, since doing this, I am no longer able to access the GUI interface of the modem. I can get to it if I attach the modem directly to one of my computers; but is there some way of accessing the modem GUI through the DLink 4100, without doing that or messing up any other network settings? Perhaps some entry in the Routing Table?