Port forwarding through my personal (not rented) Arris Surfboard Modem

Back when I had Comcast in California, all I had to do to port forward my webcam was set it up in my Netgear router, and it passed through my Arris Surfboard 8200 cable modem. Moved to Las Vegas, Cox Internet apparently won't allow port forwarding unless I waste $$ every month to rent a Cox modem. Same modem as I already have. I used to work for Arris, even beta tested this modem, so this is very frustrating. If there is a way around this without changing modems, I'd love to hear it.