ModemManager vs NetworkManager (and the overlap of functionality) : Best Practices

[Robert Colvin]

Hi!

Firstly, I don't believe this topic is handled in the documentation for either Modem Manager or Network Manager, but if it is I apologise and humbly request to be pointed in the right direction. I have looked through https://modemmanager.org/docs/ (FAQ, ModemManager, the lib* manuals and come up empty)

My basic question is what does NM do, vs MM and what is best practice 1) in general but 2) when they overlap?

The most solid information I have found is

"ModemManager is a system daemon which controls WWAN (2G/3G/4G/5G) devices and connections.

Alongside NetworkManager, ModemManager is the default mobile broadband management system in most standard GNU/Linux distributions (Debian, Fedora, Ubuntu, Arch Linux…), and is also available in custom systems built with e.g. buildroot, yocto/openembedded or ptxdist."

but this leaves me with more questions than answers (after playing for a while)

As I understood it, NM was responsible for managing the modem itself, whereas MM would handle tasks like automatically failing over a wireless network to a cellular connection - but would rely on NM to manage the interface to the modem. But in this "simple" task there is some overlap/grey area - for example, a cellular data connection requires things like APNs, where should that fall? it seems it has landed in both NM and MM. 

so, what is the best practice? what should NM manage and what should MM manage? If something goes wrong - what should the debug process be? 

I have had first hand experience in this, though I assumed it was a Network Manager issue . I made a post to the NM list here https://lists.freedesktop.org/archives/networkmanager/2023-February/000026.html - essentially, I have a modem that is on a serial port; modem manager can see it, but Network Manager is unable to setup a connection with it - the specific error is "failed to connect 'r412m_serial': Connection requested IPv4 but IPv4 is unsupported by the modem." -> given in two months there has been no response, maybe its a modem manager issue?

p.s this thread is regarding best practice of working with NM and MM; I will raise a separate thread on the specific issue of the r412m over serial

-- 
  Robert Colvin
  punk.spot9096 at skrapost.net