said by harald:
Comcast has furnished you with router/modem combination. You need to turn off the router portion, i.e. turn the Comcast router into a bridge, and connect the modem to a switch. Your two routers then connect to the switch.
That can only be done with the business class gateway box by a Comcast tech, not the customer. Also, doing that would kill the customer's static IP addresses since Comcast only assigns static IP addresses to their gateway box if it is actually being used as a gateway router.
What the OP describes doing should work with no problems (except for trying to use port 445). I used to operate multiple servers behind the Comcast business gateway and a secondary router (a Cisco RV082) with no problems. Most likely there is just a configuration problem with either the OP's secondary router, or the server.--
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