Cable Modem Dual Ports

The only way to use both ports is with either two IP addresses, or linking them to get speeds over 1G.

If you need devices on separate networks, get a router that can create VLAN's to keep them isolated.

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@Jon4t9ers wrote: ... I have IOT devices that I want to be totally separated from the rest of my network devices.

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I know of no single device that would do what you want. You may find some food-for-thought in the discussion of Steve Gibson's "three router" approach to IOT security at https://pcper.com/2016/08/steve-gibsons-three-router-solution-to-iot-insecurity/.

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@Jon4t9ers wrote:
Dual IP is not available in my area. Another option that would work for me is if the ports would be isolated from each other. Is there a cable modem that allows that? I have IOT devices that I want to be totally separated from the rest of my network devices.

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They are phasing it out but if you like I can escalate this for you to the Comcast corporate employees that are available to these boards ? We've seen cases here where they have been able to get this accomplished for customers even when it is not listed in their rate cards, YMMV. You should get a reply here in your topic.