Arris Arris CM450: Modem & WiFi Router

Arris modem is just a modem with one port ? Most isp arris modems are also routers is why I ask...

Connection test works. It's connected fine. Then I go to multiplayer test and get an error "Can't get Teredo IP address"

Details as to my config.

Cable goes to Arris modem.

Arris modem is set to bridge mode.

Arris modem connected via ethernet to Apple airport extreme, which acts as wifi router for my house.

airport extreme ALSO has an ethernet cable connected directly to the xbox one.

But I'm still getting strict nat.

Plus the "can't get teredo IP" error.

Is it an Arris gateway (modem and router) by any chance?

There are a lot of suggestions in this thread regarding your Xfinity gateway (which is actually made by Arris):

forums.comcast.com/.../1239977

The main one that is repeated--combos like the Arris are problematic and you should replace it with your own separate, quality modem and router--is the best one. However, there are a few other suggestions that involve keeping the Arris. One is to have
it put in bridge mode and use with your own router. Another is to disable all parental control settings on the Arris and set it to trust the Xbox. A third is to set the Arris wireless encryption to WPA2-PSK(AES) instead of AES/TKIP (never use TKIP, it is
vulnerable anyway). Try those and see the above thread for details.

The modem is an Arris and the router is a Netgear WNR 1000 v2