I have an (almost) identical setup (except I am using the AC810S), and even had the same DNS hangups (I used the 188.8.131.52/184.108.40.206 servers to fix that).
In my case though I want use DDNS from the 8900. To do that I figured I needed to use the IP passthrough feature in the 810 to pass the public IP address to the Billion router rather than the 192.168.1.4 from the 810. Unfortunately when passthrough is activated I loose the Internet connection and the 810 is inaccessible, requiring a factory reset from the 810 display. There is a note on the 810 web interface saying that passthrough only works on Windows and not a Mac, but doesn't say why this is the case nor does it mention routers.
Has anyone else tried that and succeeded, if so, how?
I found this link that suggests maybe a solution is use a Dovado Tiny modem between the 810 and the Billion router may work.
Hi. Could you let me know how to set the cloudflare?
I can't find that setting from the router.
I am so annoying to click the reload button again and again.
Definately, it's ok when I connect to AC800s directly.
On a billion router it's under Configuration > LAN under DHCP Server. Untick "use router's setting as DNS server" and enter the cloudflare (or other) DNS servers there.