Static vs DHCP setups from ModemManager in OpenWrt

Aleksander Morgado aleksander at
Thu Jul 15 19:54:17 UTC 2021

> >> After restart of ModemManager and then ifup wwan, reconnection is successful.
> >>
> >
> > Strange. What modem is this?
> Sorry to add to the posts, but further testing shows another case where
> this recovery didn't help. I don't have a good log of this, but it
> appears that the ppp connection doesn't fully complete and pppd
> times out.  In this case, we need to power cycle the modem - fortunately,

Oh, is this AT+PPP based really? You should have started from there :)
Being a Quectel chipset, is it by any chance Qualcomm based and you
could use QMI instead of AT+PPP? Or is QMI not available? What about
MBIM? Anything better than AT+PPP will definitely give you less

> this is something that is easy to do for us (and previous testing
> shows we need to power cycle the USB controller too), but of course
> it leads to a lot of churn and connection taking time.

Sometimes, though, this is the only way to recover. Sometimes you may
be able to recover just by forcing an IMSI detach and re-registration
(e.g. going into low-power mode temporarily); some other times you can
recover requesting a module reset in a controlled way via AT or QMI,
some other times you may need to instead toggle the RESET pin, and the
last and most drastic solution is always to fully cut power.

> This would appear to be a bug with the modem. Obviously there isn't
> much you can do about this, but I want to be clear about the different
> cases we are dealing with.

The openwrt integration does not have per se a way to attempt to
recover "dead" modems, or modems that by one reason or another don't
connect any more. I've worked preparing multiple types of setups like
those and I've always written customized "wwan monitor" programs to do
that, depending on how the modem is integrated in the system.

> Development wise, it seems like this is going to be a bunch of incremental
> improvements to iron everything out.

Heh, welcome to this world :D


More information about the ModemManager-devel mailing list