DNS and MTU

[Tom Isaacson]

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
/var/run/systemd/resolve/resolv.conf
with the DNS settings, but /etc/resolv.conf gets setup with:
# Generated by NetworkManager
nameserver 127.0.0.1

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

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: 100.95.39.213
                     |     prefix: 30
                     |    gateway: 100.95.39.214
                     |        dns: 198.224.183.135, 198.224.182.135
                     |        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?

Thanks.

-- 
Tom Isaacson