NetworkManager, ModemManager, and pppd

[Harry Mander <harrymander96 gmail com>]

Hi,

I have a PPP connection brought up by pppd running on a ttyUSB connection to an LTE modem, which is managed by ModemManager. When pppd is started after simple-connecting the modem using ModemManager it is able to get an IP address fine (which can be seen from ifconfig and ip route etc.) and I can connect to the network using the modem. However, nmcli shows the ppp0 connection as disconnected.

How can I configure NetworkManager to see the PPP connection properly? Is it possibly related to the pppd plugin since we have libnm-ppp-plugin.so present in /usr/lib/NetworkManager/1.14.4 but the log does not show any pppd plugin being loaded:

NetworkManager[285]: <info>  [1552534718.0779] Loaded device plugin: NMAtmManager (/usr/lib/NetworkManager/1.14.4/libnm-device-plugin-adsl.so)
NetworkManager[285]: <info>  [1552534718.1004] Loaded device plugin: NMOvsFactory (/usr/lib/NetworkManager/1.14.4/libnm-device-plugin-ovs.so)
NetworkManager[285]: <info>  [1552534718.1181] Loaded device plugin: NMWifiFactory (/usr/lib/NetworkManager/1.14.4/libnm-device-plugin-wifi.so)

This is running on an iMX7 based board using Yocto. I have added 

--enable-ppp=yes
--with-pppd-plugin-dir=${libdir}/pppd/2.4.5

to the networkmanager recipe file.