As far as I understand the RED device itself doesn't connect to the internet itself. you will have to use a router/modem device for that and hook up the RED to that (From what I read the router should provide DHCP functions so the RED will work automatically).
I'm confused about what exactly is so uncommon... this is a branch office device. I would say in a branch office you could roughly have - let's say 10 people. If you're using a DSL line with a fixed IP you would enter that connection information in your SOHO router device and just connect the red like you would a normal host behind the router which will then be you new "gateway" kind of thing. It behaves like a standard ethernet port on your asg and must be confgured accordingly...