This is a question and a solution of sorts.
I canceled by cable TV / Home Security and upgraded my internet to a gig.
Then I purchased the Ring home secuirty. $100 for a year of monitoring is a good price.
The one issue I had is I can connect all the wireless devices to the Xfinity WIFI but they can't connect to what every server they are trying to connect to.
I went round and round with both Ring and Xfinity. Ring said it was a firewall issue. Which would make sense. But I am a IT Professional and I know that the firewall on the Xfinity device was set to allow everything in. Wide open. So that wasnt' the issue.
I still had my Netgear R8500 Router so I connected it to the Xfinity modem directly and then connected the Ring system to it via WIFI.
So now I have the Ring connected to the SSID of the Netgear and the outside interface of the Netgear connected to the Xfinity modem.
And it works. Makes absolutly no sence. Why would the Ring not work on the Xfinity Wifi but work just fine when it is masked behind my Netgear on its Wifi?
Unless Xfinity is activly blocking Ring when it is on its Wifi. Maybe it sees it now as a Netgear device and not a Ring device?
Just a thought.
Try disabling the Xfi advanced security feature and see;
Also bear in mind that If you are hang a stand-alone / separate router off of the gateway device, and the gateway is not in *bridge mode*, you are cascading 2 routing devices which results in an undesirable "double NAT" condition on your home network.
Google "double NAT" for info about it's potential pitfalls.
Not really an answer but I had tons of issues with the Ring Floodcam working with the comcast router, couldn't get the live view, disconnects, etc, of course I was going in circles between comcast and Ring until I finally had it and got rid fo the comcast router and put some high end Netgear modem and router and the problem stopped (well the speed issues with comcast I keep having on my 2 houses, I get less than 1/3 the promised speed with new gigabit equipment)
I understand the double NAT.
What I don't understand is why the Ring works just fine while connected to my secondary router's wireless and wont work while connected to the Xfinity wireless.
In other words it is only working WHEN double NAT is in place.
That's why I am renting their modem.
Comcast told me that if I rent their modem I could get unlimited data for another 25 a month. Now I find out that isn't true so I am considering putting my own modem back in place.
Not to mention the interent has been bouncing up and down all week. Really getting ticked off with their sudden inconsistancies.