RFC: AT-controlled USB-Ethernet cellular modems: extend comgt-ncm or new netifd protocol?

[Enrico Mioso]

On Sun, Oct 04, 2026 at 01:22:25AM +0200, Felix Baumann via openwrt-devel wrote:
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> Date: Sun, 04 Oct 2026 01:22:25 +0200
> From: Felix Baumann <felix.baumann at freifunk-aachen.de>
> To: Michael Wyraz <michael at wyraz.de>, Michael Wyraz via openwrt-devel
>  <openwrt-devel at lists.openwrt.org>
> Subject: Re: RFC: AT-controlled USB-Ethernet cellular modems: extend
>  comgt-ncm or new netifd protocol?
> 
> Hi,
> 
> I'm confused. What are you suggesting:
> Aren't NCM and RNDIS mutually exclusive? 
> 
> RNDIS is about to be phased out. It's been deprecated for a while and a security nightmare. It ought to die. (my opinion, I'm not speaking for anyone on OpenWrt's behalf)

Eheh, yeah. But we should also face reality and cellular modem firmwares.
When you should work with a modem, changing it's firmware settings is not always possible or desirable, and you may find yourself stuck in a situation where it's not easy to set things as they where in the beginning.

If I understand it correctly, what they are facing is a modem that works overRNDIS and handles things so that the DHCP state of the host may end up out of sync with the cellular network state, so they need to keep things in sync by:
- polling the AT port or listening to the AT port to determine the current situation
- re-triggering a DHCP lease in case it's needed.

Thanks,
Enrico

> 
> <https://www.phoronix.com/news/RNDIS-Disable-Linux-2026-Patch>
> 
> Regards
> Felix Baumann
> 

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