Setting up Sierra Wireless Aircard 340U as cell backup PPP interface

cwhorning

Hi all,

I'm trying to set up a Sierra Wireless AirCard 340U as a cellular backup WAN for pfSense. This AirCard was previously used in a Cradlepoint router before we transitioned to pfSense.
The device is plugged in and detected correctly. It shows all interfaces, and I can connect to it using cu -l /dev/cuaU0.1. The APN we are using is PSMTNEOFIN as that is what worked when we were using the Cradlepoints. I ran the following AT commands which all worked:

AT - Responded OK
AT+CPIN? - Responded READY
AT+CSQ - Responded +CSQ: 22,99
AT+CREG? - Responded +CREG: 0,1
ADT*99# - Responded CONNECT 100000000
AT+CGPADDR - Responds with an IP address
AT+COPS? - responds +COPS: 0,0,"AT&T",7
AT+CGDCONT? - responds with the APN (PSMTNEOFIN)

It seems like the aircard is working based on that so it must be something I am doing wrong in pfsense. The current config looks like this:

Link Type: PPP
Link Interface: /dev/cuaU0.1
Country: United States
Provider: AT&T
Phone Number: *99#
APN: PSMTNEOFIN

I assigned the interface and enabled it with this configuration:

IPv4 Config type: PPP
IPv6 Config Type: None
Block Private networks and loopback addresses: unchecked
Block bogon networks: unchecked

But it shows up as down in interface status. Below are some of the relevant log entries:

Nov 5 12:10:27 ppp 64840 [opt2_link0] Link: reconnection attempt 14 in 3 seconds
Nov 5 12:10:27 ppp 64840 [opt2_link0] LCP: Down event
Nov 5 12:10:27 ppp 64840 [opt2_link0] Link: DOWN event
Nov 5 12:10:27 ppp 64840 [opt2_link0] MODEM: chat script failed
Nov 5 12:10:27 ppp 64840 [opt2_link0] CHAT: The modem is not responding to "AT" at MomCmd: labeell.
Nov 5 12:10:26 ppp 64840 [opt2_link0] Link: reconnection attempt 13
Nov 5 12:10:23 ppp 64840 [opt2_link0] Link: reconnection attempt 13 in 3 seconds

Could it be the device just doesn't work with pfsense and I have to buy something different for our cell backup solution or is it something I misconfigured?

Any information would be very helpful!

Thanks!
Connor

patient0

@cwhorning I can't help with the technical side but searching the internet comes up with a thread on the OtherSense and the user writes in April 2025 (on the third page):

"Well it seems all this work has been for nothing. AT&T has discontinued PPP support for its "Broadband" APN, so now unless someone has a better idea, I've got another paperweight."

Do you use another cell service which is still available (or was the user misinformed)?

stephenw10

Hmm, that fact it shows it's not responding to 'AT' seems to point to something lower level that the APN. Like maybe the port is still open from the CLI?

What do the logs show at the first connection attempt?

cwhorning

@stephenw10 Here are the logs for the first reconnection attempt:

Nov 7 09:52:52 ppp 9031 [opt2_link0] Link: reconnection attempt 2 in 1 seconds
Nov 7 09:52:52 ppp 9031 [opt2_link0] LCP: Down event
Nov 7 09:52:52 ppp 9031 [opt2_link0] Link: DOWN event
Nov 7 09:52:52 ppp 9031 [opt2_link0] MODEM: chat script failed
Nov 7 09:52:52 ppp 9031 [opt2_link0] CHAT: line 358: label "MomIdentGeneriicc" not found
Nov 7 09:52:52 ppp 9031 Label 'MomIdentGeneriicc' not found
Nov 7 09:52:52 ppp 9031 [opt2_link0] Link: reconnection attempt 1
Nov 7 09:52:48 ppp 9031 [opt2_link0] Link: reconnection attempt 1 in 4 seconds
Nov 7 09:52:48 ppp 9031 [opt2_link0] LCP: Down event
Nov 7 09:52:48 ppp 9031 [opt2_link0] Link: DOWN event
Nov 7 09:52:48 ppp 9031 [opt2_link0] MODEM: chat script failed
Nov 7 09:52:48 ppp 9031 [opt2_link0] CHAT: The modem is not responding to "AT" at MomCmd: labeell.
Nov 7 09:52:47 ppp 9031 [opt2_link0] LCP: LayerStart
Nov 7 09:52:47 ppp 9031 [opt2_link0] LCP: state change Initial --> Starting
Nov 7 09:52:47 ppp 9031 [opt2_link0] LCP: Open event
Nov 7 09:52:47 ppp 9031 [opt2_link0] Link: OPEN event
Nov 7 09:52:47 ppp 9031 [opt2] Bundle: Interface ng0 created
Nov 7 09:52:47 ppp 9031 web: web is not running
Nov 7 09:52:47 ppp 9031 process 9031 started, version 5.9
Nov 7 09:52:47 ppp 9031 Multi-link PPP daemon for FreeBSD

stephenw10

@cwhorning said in Setting up Sierra Wireless Aircard 340U as cell backup PPP interface:

Nov 7 09:52:52 ppp 9031 [opt2_link0] CHAT: line 358: label "MomIdentGeneriicc" not found

Try putting in the modem init string: &F&C1&D2E0S0=0${temp}

cwhorning

@stephenw10 Adding the init string and then changing the gateway monitor to 8.8.8.8 brought it up and working. Thanks for your time and help!

stephenw10

No worries. Yeah that appears to be a bug in mpd5 that some modems hit.