I've been trying to add a port to my port forward since I've had this thing in June and I haven't been able to get any assistance from Xfinity on the issue.
We're Having Some Trouble
Please try again. If the problem persists, check back later.
It never works.
Connect->See Network->More/Advanced Settings->Port Forwarding
Try disabling the Xfi Advanced Security feature as a work-around for now and see. It's buggy ! And there is currently no way for an end-user to be able to whitelist anything;