I have finally gotten a second dynamic public ip address for provisioned on my Arris SB8200 Privately owned modem. I would like to share how I did it after hours of aggrivation without visiting the local xfinity store. To the point: When you call comcast go straight to the billing department. On your browser be logged into your account and go to this link: https://www.xfinity.com/support/rate-card/ Click View PDF. Find "Additional IP Addresses" on the rate plans under "Xfinity Internet" just below "Modem Rental" if it is available in your area. Tell the Service Rep you want to purchase an "Additional IP Address" and tell them the exact amount of the rate that is listed and that it is below "Modem Rental". Some will argue with you and say that is impossible or it is not available or try to transfer you to tech support. Don't let them do any of those. If you see it on your rate plan it is available and have them search the rate plan again to add the service. Once you accept the terms and it gets added your modem will reboot and have a second IP Address on port 2. IMPORTANT!!! BEFORE YOU HANG UP, CHECK TO SEE IF IT IS WORKING! ( Devices must be set to obtain ip address automatically and be plugged into modem before it reboots! If they are not since there is no DHCP Server they will not obtain an IP Address. To fix this plug all devices in and power cycle your modem.)
Second note: If you are using a gateway and not a stand alone modem, the second IP Address will not be seen; as the gateway uses routing to administer DHCP served addresses to the ports on the back of the gateway.
I did this so I can have my home router plugged into one port and a gaming console plugged into the second port to achieve NAT type 1. I hope this helps someone. Good Luck!