Purchased Dual Band Modem Setup

Are you saying that the other gateway is also connected to the second ethernet port on the 8200 cable modem ?

yes 

O/k you would need to get a second public / WAN IP address assigned from Comcast in order for that port to be active. The problem is that they are phasing out that feature. See below;

First, check the "Rate Card" for your local area to see if that feature is even available anymore. Seems that it is being phased out;

https://www.xfinity.com/support/rate-card/

It's a PDF.

Scroll down to "Xfinity Internet" and look for "Additional IP Addresses".

If nothing is listed then it's likely to have been discontinued in your local market area.

Yes.

Thank you for the help. Unfortinitately I didn't see the Additional IP Addresses on the list. One thing Abode recomended to me was checking that i was recieving dualband internet (2.4 and 5.0GHz), the device is supposedly only 2.4Ghz compatible. However isn't 2.4GHz only specific to Wi-FI and not a LAN Connection. 

THe Abode version i have doesn't connect to Wi-Fi, it only has a LAN connection. That is why the recomendation was so suprising to me?

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@piette13 wrote:

I recently swaped my internet modem from an xfinity rental to an Arris SB8200 from the xfinity compatible device list. I have the modem setup and working great with my Wi-Fi router. However it is also directly connected(ethernet)  to an Abode gateway that is now longer able to connect to the internet. What is the likely casue of this issue? 

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Your new WiFI router manages your network connections. In your new setup, you're supposed to connect the Abode gateway to your WiFi router, not the SB8200. 

Thank you, I misunderstood your instructions. Plugging it into the router fixed the issue.