Unable to connect 4G LTE modem Netgear LB2120

[marmot74]

Hi,

New with Opnsense - switching from Ubiquiti.
I use a 4G SIM as my main network connection. After browsing these forums and that from PFsense I bought a Netgear LB2120 modem which seemed to be compatible out of the box.

What I have done so far :
> Full setup and update of Opnsense (Protectli box)
> Setup Netgear LB2120 in bridge mode with ethernet on WAN port
> Create Point-to-Point device in Opnsense in PPP with parameters similar to that found on the LB2120. I selected the only Link Interface prompting on the screen /dev/cuaU0

I'm running OPNsense21.7.7-amd64 and FreeBSD12.1-RELEASE-p19-HBSD

Despite all this, I am getting errors in the logs
For instance :
"LCP: Down event
Link: DOWN event
MODEM: chat script failed
CHAT: The modem is not responding to "AT" at ModemCmd: label.
Link: reconnection attempt 1
Link: reconnection attempt 1 in 1 seconds
LCP: Down event
Link: DOWN event
MODEM: Fail to open serial port /dev/cuau0 on speed 115200
uu _lock(cuauo): device in use
LCP: LayerStart
LCP: state change Initial -> Starting
LCP: Open event"

Anyone with experience with Netgear LB2120 can help and share their config with me please ?
Could it be that I should be using another Link Interface ? I am not sure how this works to be honest...

 PS : I saw a few posts mentioning something about a non-standard TCP/IP implementation from Netgear. I admit I have not had time to try the proposed solution, I will try this later this week. https://forum.opnsense.org/index.php?topic=25727.msg123949#msg123949

Thanks in advance for your help.