OpenWrt for Netgear Nighthawk X4S C7800

For Developers
1

Hello

Trying to figure this out on my own but struggling. I have a Netgear Nighthawk X4S AC3200 (C7800) that I purchased in the US while using Comcast. I had it shipped to NZ, but NZ ISP largely use an Optical Network Terminal (ONT) meaning the Coax cable cannot be used on my router/modem combo. Instead the ONT converts the data to ethernet and plugs directly into whatever router/modem you have.
To address this, I had hoped to use bridge mode and just use it as an AP, however, Netgear OS does not have a bridge mode function built into its software. I tried plugging the ethernet cable in from the ONT into port 1 of the C7800, but that too fails. The C7800 does not see port 1 as providing it with internet. It appears to only function with the coax plugged in.
So I turned to OpenWrt in the hopes of using the C7800 instead of the wimpy existing hardware provided by NZ ISP. However I cannot find the exact model of my device to flash the firmware to OpenWrt. I found that version 19.07.7 supports a Netgear Nighthawk R7800 which is similar to my Nighthawk C7800, but I didn't want to just install without checking here first. Can I install OpenWrt on my device, even though it isn't explicitly supported?
Also, in the event I need to go back to Netgear OS to try and sell it back in the US, how can I get the device back onto Netgear's OS? According to Netgear's own documentation for the C7800, "Firmware upgrades are pushed down by your ISP.". Additionally, Netgear's firmware version page doesn't have a way for me to download the firmware should I need to roll back.
I'm just trying to either use the router/modem in bridge mode or set it up to funnel traffic from ethernet port 1

Tl;DR:

  • Can I use OpenWrt 19.07.7 using software for Netgear R7800 despite having a Netgear Nighthawk X4S AC3200 (C7800)?

  • Can I use OpenWrt to either put the C7800 into bridge mode OR have it route traffic from port 1 instead of only the coax cable?

  • How do I get the firmware back to Netgear's OS in the event OpenWrt does not work for the device?

Thank you!

2

No.
This is the first time I hear from C7800 and after googling for it, it looks totally different. And it has the cable modem part. Some reviews mentioned processor speeds that differ from R7800.

Despite the similarity in the number, it is a different beast, and OpenWrt for R7800 is very very likely not compatible.

3

You can find out yourself if your device is supported, if yours isn't listed explicitly, it isn't supported. There are no generic images and trying to install the firmware for another router on your device is pretty guaranteed to be fatal.

In case of the Netgear c7800, we're talking about a very different device than the r7800 or the d7800, using a completely different SOC (which isn't surprising, as there are basically only two vendors present in the market for cable modems). The device coverage for cable modems (including modem-routers) under OpenWrt is non-existent, as there are no drivers for the modem part, nor the FXS/ DECT functionality - and in this case not even the SOC itself (interestingly the wireless part would be supportable, but that doesn't matter as there is no SOC support at all). Given that cable modems need to cryptographically authenticate their firmware against the ISP, there is no hope for this device category to 'ever' be supported by OpenWrt either.

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