When I troubleshoot Comcast business internet services I usually call support 2 or 3 times until I get a technician that's familiar with my issue. That technique hasn't worked for me with residential service. The telephone reps in residential accounts are either (1) not trained beyond the script or (2) forced to stay on script despite what they know. I spoke to three different techs who didn't recognize the term "Network Address Translation." I offered to give a primer.
I originally configured my neighbor's residence with Comcast's RCA cable modem into a Linksys WAP. I'm certain that Comcast/Xfinity randomly changed their service to this account, providing a type of DHCP that the RCA could not consistently interpret; service worked for less than a minute after a power cycle. One technician eventually admitted to me that the service was "in limbo" and "needed to be patched".
This was frustrating. My neighbor had no service for about a week.
The replacement modem came in the mail, a Ubee, maybe 3.0. It passes the public DHCP straight to the device on the other side. The public IP worked with a laptop, but the Linksys couldn't get an address.
I'm useless if you take away IP technology, gateways, and such. My troubleshooting tools are out the window. I don't know how to talk to the box. Apparently Comcast techs don't either. They can tell me that the box is on. They can't tell me if a user is connected; ie: no routing table.
I've been browsing a Comcast support forum and other sites. Complaints are pretty varied and often focus on game consoles. I'm looking for one page that explains this awful technology, and perhaps gives me ways to troubleshoot it, and setup a NAT device.