I'm also using Comcast and have multiple IP Numbers for all of my machines. It has been this way for nearly two years
Now they tell me that I can only have one IP number for the amount I'm paying, If I want the multiple IP number package it will cost me another $50.00 a month..............Not!!!!
I'm glad I'm moving to Maine and can say adios to all of this nonsense.
Boo on Comcast..................