Can't pull IP from Comcast modem.

I have the latest non beta Astaro that I am trying to get running at a friends house. I have tried everything I can think of, and find online, but no matter what I do, I am not pulling an IP from the Comcast cable modem. Comcast says I do not need to do anything with the MAC since the modem holds all the data. Is that correct? Has anyone had any success with this?

Working setup

modem -- router -- network

Non working

modem -- Astaro -- network

Thanks for the help.

C68