After many hours of research and conversations with Google I have finally got this working. As a bit of background my house is connected to NBN FTTN so I have VDSL2 modem and the Google Nest Wifi is connected to one of the LAN ports on the modem to the WAN port of the Google router. I have a combination of wired and wireless devices and the XBOX’s are connected via wired Ethernet to the Google router LAN port via a couple of unmanaged switches. The following are the steps I took to achieve Open Nat on 2x Series X’s, 2x One S’s and a One X without double NAT.
88 to 88 UDP
500 to 500 UDP
3544 to 3544 UDP
4500 to 4500 UDP
50000 to 50000 TCP/UDP – UPNP does seem to work for this port but I have forwarded them anyway.
89 to 88 UDP
501 to 500 UDP
3545 to 3544 UDP
4501 to 4500 UDP
51000 to 51000 TCP/UDP - This is the second XBOX port as an example.
90 to 88 UDP
502 to 500 UDP
3546 to 3544 UDP
4502 to 4500 UDP
52000 to 52000 TCP/UDP - This is the third XBOX port as an example.
If by chance you can only use port 3074 for your XBOX’s then you can use the same philosophy above for each XBOX port as follows.
3074 to 3074 TCP/UDP – 1st XBOX
3075 to 3074 TCP/UDP – 2nd XBOX
3076 to 3074 TCP/UDP – 3rd XBOX
I got the port number from below but there are plenty of sites with this info.
Hopefully this can help someone and save them some time. Good Luck!