I just cannot get port forwarding to work consistently with my xfinity gateway. I just wanted to open two ports to my local Mac for ssh and Plex access. The last time I tried I literally couldn't get any phone support for it at all, no one knew what I was talking about. They sent a guy to my home (!) to fix it. He didn't know anything about it, nor did his supervisor, who also tried to tell me port forwarding wasn't supported in home gateways, got to get a business gateway. In desperation I just had them replace the gateway, and it worked! For about a day, and then it stopped working again.
this all used to work.
No longer works in the admin tool on the gateway, but should work under "advanced" settings in the xFi app or the xFi portal on the Xfinity home page.