Re: ModemManager and muxed network interfaces

[Aleksander Morgado <aleksander aleksander es>]

Hey Thomas,

> > I'm working on setting up muxed network interfaces with ModemManager
> > so that e.g. you can connect to multiple APNs at the same time, each
> > with its own subnet on a different virtual network interface link
> > created from the "master" wwan modem interface. These links can be
> > done either with mbim (using VLANs) or qmi (using the built-in muxing
> > capabilities of qmi_wwan or with rmnet).
> >
> > Now, in order to integrate this with NetworkManager, the main
> > difference that NM will see upon connecting a modem through MM will
> > be that the data port reported in the Bearer info that
> > Simple.Connect() returns is no longer the master wwan interface, but
> > a new "qmimux0" interface (name varies depending on the kernel backed
> > used).
> >
> > I already have this logic setup in a custom branch, but I'm lacking 2
> > things right now:
> >   * When setting up the muxing support, we need to configure the MTU
> > of the master wwan interface to a specific value that the modem tells
> > us to use (the maximum data aggregation size).
> >   * And also, before NetworkManager can bring up the "qmimux0" link
> > interface, the "master" wwan modem interface needs to be already up
> > or the link ifup will fail.
> >
> > I can definitely add those two things to the ModemManager connection
> > logic, but wanted to ask, is there any way NetworkManager could setup
> > both the master network interface AND then the muxed qmimux0
> > interface? E.g. if MM exposed all those things in DBus, could NM
> > setup both those interfaces? Or is that too much change in the NM
> > logic because it truly expects to setup one interface at a time?
> >
> > I think the way to go is to add it in MM, so that theoretically NM
> > does not need to do absolutely anything, but wanted to ask first
> > anyway.
> > Any comments or suggestions?
>
> Hi Aleksander,
>
>
> NetworkManager's primary means of configuring something is by having a
> connection profile to begin with.
>
> If the master network interface requires non-trivial configuration,
> then it probably would also require a profile in NetworkManager, and
> the "port" interface would refer to that controller interface.
>
> On the other hand, for vlan interfaces/profiles you don't necessarily
> need a profile for the parent device. Specifying the parent (interface
> name) is enough.
>
> Also, that one connection profile in NetworkManager can control
> multiple "devices", is not new. That also happens when you activate a
> modem connection. There is the control port (a NMDevice) but there is
> also the actual interface with the IP configuration. I think that is
> currently not solved well and is in dire need of improvement, but in
> general, that there are multiple "devices" that are configured by one
> profile is also viable.
>
>
> On the other hand, if MM can abstract all of this nicely, then indeed
> it seems good if MM does it. That would also (theoretically) simplify
> it for users who don't wnat to use NM but MM.

I went ahead and added all the necessary logic in MM, because the
master/parent interface setup is not trivial; e.g. there is a case
where the master MTU needs to be set before the interface is switched
to raw-ip in the kernel, and also links pre-created before the master
link is brought up, and several other magical things to do here and
there. As you said, MM can abstract all of this nicely.

In the NM side, the only thing that you would need to know is whether
you want multiplexing support or not. As of now, I'm preparing a new
"multiplex" setting in the MM connection settings that accepts 3
values: "none" (multiplex must not be used), "requested" (multiplex
should be used if available) and "required" (multiplex must be used or
otherwise fail). Right now the absence of the setting means "none", so
for now NM won't request multiplexing. In this next MM 1.18 dev cycle,
and if the multiplexing support is stable enough, we may change that
absence to mean "requested", or otherwise maybe suggest one additional
explicit NM setting to let users to configure it, or something like
that. The target is to allow the connection manager (NM or some
others) to bring up multiple connection settings over a single modem
object, as that is what this multiplexing feature provides (e.g. one
APN for Internet, one APN for a private corporate network, one APN for
MMS...)

-- 
Aleksander
https://aleksander.es