Routing v6 subnets to my static gateway

What is the magic for Comcast to route subnets of my /56 to a static gateway on my perimeter?

I have a Cisco 3845 running IOS 15.x on my perimeter (v6 only) with a DHCP address (PD ::192.168.23.2/64) that I want four /64 subnets routed into, such as PREFIX:1002::/64. Currently, packets on the LAN side of the gateway go out to the Internet, touch the destination, but replies are lost somewhere within the Seattle Comcast cloud.

I have v6 devices on the permeter but I need to reach devices on the LAN side of the gateway from the Internet. Of course, I also need my devices to reach out to the Internet preferably NOT via NAT. Generally, these devices are statically assigned. Firewalling is, of course, my problem.