Joe has switched his parents over to Comcast for internet access and TV, and he's having a hard time opening ports through the router for their alarm system. What can he do? Rich says to try what Xfinity recommends here - https://www.xfinity.com/support/articles/port-forwarding-xfinity-wireless-gateway. If that doesn't work, then it may be that the port forwarding capability of Xfinity is limited. Rich also says to make sure the firmware is updated.
If all else fails, request a newer router. Often you get equipment from your ISP, and it's really outdated. So request a newer, updated one.