OK ... given the answer with respect to Xfinity Home equipment, It seems to me that Xfinity Home needs to supply it's own modem, and a cable splitter. The entirety of Xfinitiy Home should be isolated from any and all of my Xfinity Internet connection. It should create and manage it's own network connection completely isolated from the Xfinitiy Internet connection whose complete bi-directional operability, and addressability from the Internet "cloud" is paid for separately in my bill. I don't pay to share that connectivity, especially with equipment that blocks my operability.
Consider this ... the Xfinity Home router, sitting instream between the Xfinitiy Internet modem, and my home's connections (which may or may not include a router, MASKS the WAN-facing network IP address from my home network (and my router). If there is no provision for that Xfinitiy Home router to do NOTHING but intercept its needed ports and leave everything else to my home network (for my administration), then that device is UNWELCOME on the Internet connection I pay for because it destroys my ability to use that Internet connection as a bi-directional connection.
It uses the WAN-facing public IP address (one you can "ping" from anywhere in the Internet "cloud") and it provides on it's output side (to the home network) what is known as a private IP address (an IP address in one of the following ranges ... 10.0-255.0-255.0-255, 172.16-31.0-255.0-255, or 192.168.0-255.0-255). A private IP address iin any of these ranges is isolated to the local area network (LAN) behind the router that hosts that IP address. It can never reach the network beyond that boundary which means the home network router can no longer be addressed in order to provide directed port access to devices on the home network.
IN ESSENCE, Xfinity Home IS VOIDING MY bi-directional Xfinitiy Internet CONNECTION TO THE Wide Area Network (WAN ... read Internet).
It seems to me that Xfinity Home's router needs to be on it's own Cable data modem and that that device needs to be provided with the Xfinity Home router and a cable splitter ... my Xfinity Internet connection (modem) belongs on one side of that splitter, Xfinity Home's connection (modem and router) belong on the other side of that splitter.
There was NEVER any representation made to me that Xfinity Home would have a deliterious effect on the facilities of the Xfinity Internet connection that I pay for.