Using ASUS DSL-AX82U with Netgear 4G LTE Broadband Modem after move to Full Fibre?

[#1]

Hello folks

Today I moved from Plusnet FTTC to Plusnet FTTP.

I have a ASUS DSL-AX82U with a Netgear 4G LTE Broadband Modem as a fallback option plugged in. That worked great whilst on the FTTC connection, as the "Dual WAN" setup on that router has an option for setting up the Primary WAN as DSL and the Secondary WAN as WAN. I had the router plugged into the phone line using the DSL port, and connected to the Netgear via the WAN port.

Now that we are on FTTP the setup has of course changed and the main internet connection is of type WAN and the cable goes from the router's WAN port into the Plusnet box on the wall.

I could not figure out a way to get the Netgear modem to still work with that setup. The Asus router does not allow the "Primary" and "Secondary" WAN to both be of type WAN in the "Dual WAN" configuration menu. I tried repurposing a specified LAN port on the Asus router as a WAN port, but that would not result in a successful failover, either.

The Asus router does have a USB-C port for 4G/5G tethering - I tried that for a minute, but even if I enable USB tethering on my phone, the failover simply won't work. 

With either option, when I unplug the network cable from the WAN port to force a failover, the internet light simply goes off and stays off. It simply doesn't seem to be looking for the failover connection anymore, like it did when I was still using it in DSL mode.

Any ideas on how to reinstate the failover on the Asus router?

[#2]

You have a bit of a problem.

The Asus manual 3.14.3 talks about Dual WAN but, as you say, you can only have Ethernet WAN once and I have the impression that your Netgear presents as Ethernet (so with DSL uses the WAN port you now need for the FTTC service).

There are a few possibilities, using what you have, does the Netgear allow a WAN connection as well as LTE and could that do the failover?

If so the Plusnet PPPoE connections would go in the Netgear and the Asus would be set to DHCP (as previously) on the Netgear.

That requires the Netgear to be fast enough using PPPoE for your full fibre connection and means you have dual NAT (which may or may not be a practical problem for you).

Otherwise (and probably my preferred approch) would be finding a USB modem that works with the Asus.

Having played that game with other routers in the past, getting the USB modem that actually works is the critical bit and routers tend to be fussy.

I couldn't find any cluses for suitable USB devices by a quick search.

[#3]

Having had a bit more of a study of the Asus manual, it may not support a USB WAN connection as a failover source anyway.

There is a hint that you choose USB or a "normal" WAN.

Dual Ethernet WAN routers are reasonably rare.

Perhaps seeing what the Netgear could do might be the best way forward.