Forewarning: The below is not officially supported and should not be used in a production environment. It's here to simply demonstrate that it's possible to configure 'unsupported' LTE modems on Avocent units.
Since there is next to no documentation for this I thought I'd provide some (hopefully) useful information for anyone else trying to get a LTE modem / dongle setup with the unit.
Firstly ensure you are running the latest firmware as more recent Linux kernels have greatly improved support for LTE modems.
For this exercise I am using a 'D-Link DWM-222 4G LTE USB Adapter'
We'll need to set the 'Moderate' security profile (System >> Security >> Security Profile) firstly (as we'll need root access over SSH)
Firstly define the APN for our mobile operator (Smarty Mobile in this case):
echo "APN=mob.asm.net" >/etc/qmi-network.conf
Ensure 802.3 is set:
qmicli -d /dev/cdc-wdm0 --wda-set-data-format=802-3
Start the modem driver:
qmi-network /dev/cdc-wdm0 start
Ensure the interface is automatically started and the cdc-wdm interface is started before bringing the interface up:
vi /etc/network/interfaces
auto lo eth0 eth2 wwan0
iface wwan0 inet dhcp
pre-up /usr/bin/qmi-network /dev/cdc-wdm0 start
If the interface does not come up automatically despite 'auto wwan0' being set you can create startup script instead:
vi /etc/init.d/S99lteconfig
sleep 15
echo "Bringing up LTE interface..."
/sbin/ifup wwan0
/sbin/ip route add 0.0.0.0/0 dev wwan0
chmod 755 /etc/init.d/S99lteconfig
ln -s /etc/init.d/S99lteconfig /etc/rcS.d/S99lteconfig
Restart the device and check whether the interface has come up:
ip addr
Lastly ensure we put the 'Security Profile' back to 'Secure' mode.