Had the xfinity home system installed yesterday and was having the same problem. After speaking to someone with Comcast and having him tell me there are 4 ports on the back of my router I decided to look elsewhere. I finally got it to work after a few various forum posts, by
- First I exposed the router to the internet.
- On the tablet provide by Comcast goto settings/advanced settings/connectivity. Once there follow the expose personal router to internet instructions.
- Then on my router I found the DMZ settings. I use the DDWRT software on my router which can be installed on pretty much every router, so you don't need to run out and buy another device.
- Login into router configuration page and go to NAT/QoS then click DMZ,
- Put in the IP address of the device you need ports open for in my case that was 192.168.1.15.
- Once I did that I was able to connect remotely.
Maybe I just got lucky but it's worth a try if you feel frusterated.