Bearer MTU not recognised by NetworkManager

[Michael Jones]

> Hi,
>
> I’m observing that NetworkManager (v1.20.2) does not recognise the MTU (=1360) exposed by the ModemManager’s (v1.10.6) bearer object and instead uses some
> default value (=1500). This seems to lead to issues which are fixed when manually setting the MTU to a lower value. When checking the NetworkManager’s
> connection settings, gsm.mtu is set to “auto". I’m observing this on a Quectel BG96 hooked up via QMI. My kernel version is 4.19.87.
>
>Is this a known issue? Is anyone aware whether this is fixed upstream?
>
> Thanks,
> Sven


See here for an analysis I did for OpenWRT's Netifd and the MTU from the
bearer.

It's not the same as your situation, so please don't think I'm trying to
provide a fix, it's simply a related issue, that's all.

https://github.com/openwrt/packages/issues/11383
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