Hi there, evan112312.
Is it just one device or all devices not showing on the drop-down?
Thanks for posting to our forums!
Just so the other customers know, this is a known issue with xFi. It's not your home network at all, it has to do with how Xfinity's servers pick up configuration data with the cable modem / router in your house. If there was a way to disable xFi and configure the modem localy (10.0.0.1 or whatever), then you wouldn't have any problems. Sometimes if you disable ip-v6 on the device you want to forward to, it will show up, but then again that doesn't always work either. Honestly, my suggestion is this. Buy yourself a decent router on Amazon, then setup your cable modem to be in Bridge mode and forget about xFi. It's not worth the trouble and frustrations you get with it.