modemmanager disconnects and not able to reestablish connection

[Aleksander Morgado]

Hey,

>
> Network-manager is not installed. Thus I do not really know which
> mechanism changes the IP settings when I call mmcli --simple-connect.
> After looking through the logfiles I think the kernel driver (cdc_mbim
> in my case) brings up the wwan0 device and dhcpcd takes care of changing
> the IP settings. Correct me if I am wrong.
>
> Here the corresponding section of the logfile:
>
> Aug  1 03:25:16 raspberrypi systemd[1]: Started USB_ModeSwitch.
> Aug  1 03:25:16 raspberrypi kernel: [   14.281840] usbcore: registered new
> interface driver cdc_ncm
> Aug  1 03:25:16 raspberrypi kernel: [   14.285363] usbcore: registered new
> interface driver cdc_wdm
> Aug  1 03:25:17 raspberrypi kernel: [   14.615873] cdc_mbim 1-1.4:2.0:
> setting rx_max = 16384
> Aug  1 03:25:17 raspberrypi kernel: [   14.615991] cdc_mbim 1-1.4:2.0: NDP
> will be placed at end of frame for this device.
> Aug  1 03:25:17 raspberrypi kernel: [   14.616799] cdc_mbim 1-1.4:2.0:
> cdc-wdm0: USB WDM device
> Aug  1 03:25:17 raspberrypi kernel: [   14.618650] cdc_mbim 1-1.4:2.0 wwan0:
> register 'cdc_mbim' at usb-3f980000.usb-1.4, CDC MBIM, 8a:12:48:88:75:b3
> Aug  1 03:25:17 raspberrypi kernel: [   14.619232] usbcore: registered new
> interface driver cdc_mbim
> Aug  1 03:25:17 raspberrypi dhcpcd[483]: wwan0: adding address
> fe80::30bd:3fa9:a4be:97ae
> Aug  1 03:25:17 raspberrypi avahi-daemon[465]: Joining mDNS multicast group
> on interface wwan0.IPv6 with address fe80::30bd:3fa9:a4be:97ae.
> Aug  1 03:25:17 raspberrypi avahi-daemon[465]: New relevant interface
> wwan0.IPv6 for mDNS.
> Aug  1 03:25:17 raspberrypi avahi-daemon[465]: Registering new address
> record for fe80::30bd:3fa9:a4be:97ae on wwan0.*.
> Aug  1 03:25:17 raspberrypi dhcpcd[483]: wwan0: waiting for carrier
> Aug  1 03:25:17 raspberrypi dhcpcd[483]: wwan0: carrier acquired
> Aug  1 03:25:17 raspberrypi dhcpcd[483]: wwan0: IAID 48:88:75:b3
> Aug  1 03:25:17 raspberrypi dhcpcd[483]: wwan0: rebinding lease of
> 80.226.70.221
>

That will not work properly, as disconnections are reported via
control port as you saw, and that would require a re-trigger of the
DHCP operation. Plus, not all modems support DHCP, and the DHCP
operation should only be run once the modem is connected via control
port.

You will need either NetworkManager to manage your wwan connection, or
a custom setup to handle the connectivity changes reported by
ModemManager. NM is definitely the easiest way to handle this.

-- 
Aleksander
https://aleksander.es