problems with QMI dual stack connections from MM - works with qmicli

[Bjørn Mork]

Aleksander Morgado <aleksander at aleksander.es> writes:

>> Some observations:
>>
>>  - dual-stack fails if default bearer is connected as ipv4 only
>
> Oh, but this is expected, isn't it? or is it not expected? I have
> always assumed that to be the case.

Yes, I guess it is expected.  It was mostly the APN change that
surprised me, complicating this further.  But I do see how that makes
sense, and ideally the default APNs should all be dual-stack.

>>  - default bearer APN changes when switching SIMs (to SIM defined APN?)
>
> Is the module switching carrier config as well when switching SIMs?

I tested with SIMs from the same carrier, but with quite different
profiles.  One was a disabled "Fixed Wireless Access" SIM I got with
this used router (The SIM slots are hidden behind a cover, and the
seller probably didn't even know about it :-) This SIM is not accepted
by the network, so there is no default bearer connected.  Our FWA thingy
does not currently support IPv6 (embarrassing). So any APN hints will
probably point to IPv4 only APNs. 

The other SIM is an old "Mobile Broadband" SIM, predating our IPv6 setup
by years. If it has any APN hints, then those are alsp IPv4 only.

So it's not surprising to me that the SIM switch causes this issue.  It
just wasn't something I thought about before it happened.  Actually, it
took me a while to notice when dual-stack stopped working after a SIM
switch.

> Please note that ModemManager has 2 different sets of settings for the
> initial APN: the settings stored in the modem (either provided by
> carrier config or set by user manually) and also the real settings
> reported by the network once it's registered. E.g. the modem may ask
> for APN "internet" and the network may successfully register the
> device with APN ("data") instead. mmcli should show both these things
> separately; the real network status settings will be reported as a
> separate bearer object.

Yes, I believe this works perfectly.  The modem profile is reset to
ipv4v6 and empty ("") APN when switching SIM.  The connected bearer is
reported as ipv4 and APN "telenor.mbb".  This is an IPv4 only APN that
could very well be a network default for that SIM.

If I manually configure the default bearer modem profile to use the dual
stack APN "telenor.smart", then it is used and the bearer is reported as
ipv4v6.

>>  - connecting multiple ipv4 or dual-stack bearers fails
>
> Wait, it doesn't fail for me here, as long as I use ip-type=ipv4
> explicitly for example.

OK, I have to retry this in a clean enviroment.

> I haven't been able to test multiple dual-stack here yet; my network
> operator allows me to use multiple IPv4 APNs but no IPv6, and I still
> don't know how to configure more than one IPv4v6 APNs in my home LTE
>
I am lucky enough to know a few APNs that are meant to address specific
PGWs. Which multiplies the number of APNs by the totalt number of PGWs.
I have no home LTE network, though.  Guess that should be part of the
Corona home office setup :-)

> There is one additional thing you didn't test, and I don't know if it
> would be useful for you or not. See this MR here:
> https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_requests/477
> That branch allows querying/modifying/deleting connection profile
> settings in devices, and it also allows requesting a connection
> through a specific profile. The WDS Start Network, in this case, just
> references the profile id that should be connected.

Will test.  So far I've just used AT commands to configure the default
bearer profile and left the rest untouched.



Bjørn