Tom Isaacson tom.isaacson at teknique.com
Tue Nov 22 08:34:53 UTC 2022

I'm moving over to ModemManager / NetworkManager integration but I'm
not sure I understand how DNS and MTU are handled.

My device has a Sierra RC7611 or RC7620 (depending on location). I'm
setting up the data connection using:
nmcli connection add type gsm ifname 'cdc-wdm0' con-name 'sierra'
connection.autoconnect yes

That works fine for data, but I'm confused as to how DNS and MTU are
supposed to be setup. Systemd correctly sets up
with the DNS settings, but /etc/resolv.conf gets setup with:
# Generated by NetworkManager

I have to delete it and setup a symbolic link to
/var/run/systemd/resolve/resolv.conf. Shouldn't Systemd take care of

Secondly, the bearer sets the MTU at 1428:
# mmcli --modem=0 --bearer=0
  General            |  dbus path: /org/freedesktop/ModemManager1/Bearer/0
                     |       type: default
  Status             |  connected: yes
                     |  suspended: no
                     |  interface: wwan0
                     | ip timeout: 20
  Properties         |        apn: internet
                     |    roaming: allowed
                     |    ip type: ipv4v6
  IPv4 configuration |     method: static
                     |    address:
                     |     prefix: 30
                     |    gateway:
                     |        dns:,
                     |        mtu: 1428
  Statistics         |   duration: 240
                     |   bytes rx: 28188070
                     |   bytes tx: 1066621

But that doesn't seem to be applied automatically? Do I have to read
it then apply it myself?


Tom Isaacson

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