Sniff/Capture LTE traffic


Target : ATH79
Investigating : qmi_wwan.c driver
Modem model drivers/net/usb/qmi_wwan.c:1475 [qmi_wwan]qmi_wwan_probe =_ "Quectel EC20 quirk, skipping interface 0\012"

I am facing an issue which looks like the ISP closes the connection pppd[15018]: LCP terminated by peerr
daemon.notice netifd: Network device '3g-wan2' link is down
daemon.notice pppd[15018]: Modem hangup
daemon.notice netifd: Interface 'wan2' is now down

However I can not tell it is not our fault.
I would like to sniff the LTE traffic to see the RPCs (Cell Search/Selection - idle state etc)

I need a tool similar to "btmon" or "hcidump" for the BT protocol.

If it is not possible please advice what is the best aproach to investigate the issue (I do not the an external LTE sniffer.)

I know knothing about the Qualcomm MSM Interface (QMI) but I do not see any possibility for capturing.


Why you use PPP with not-that-old EC20?

Please also show the output of cat /sys/kernel/debug/usb/devices

what dependencies would that be ?

ppp just "dials" into modem, so any errors are about some mismatch in negotiated feature interpertation, not that provider drops anything.

1st message edited

service@XC1:~$ uname -a
Linux XC1 5.4.124 #0 Wed Jun 12 07:01:09 2024 mips GNU/Linux

What is your modem model and why you use PPP?

[qmi_wwan]qmi_wwan_probe =_ "Quectel EC20 quirk, skipping interface 0\012"

Why PPP - the program is legacy :slight_smile:

qmi-utils I was able to build limiting to



service@XC1:(unknown)$ qmicli -V
qmicli 1.28.6
Copyright (C) 2012-2021 Aleksander Morgado
License GPLv2+: GNU GPL version 2 or later <>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

please post

ubus call system board
root@XC1:~# ubus call system board
        "kernel": "5.4.124",
        "hostname": "XC1",
        "system": "Qualcomm Atheros QCA9533 ver 2 rev 0",
        "model": "8devices Lima",
        "board_name": "8dev,lima",
        "release": {
                "distribution": "OpenWrt-8devices",
                "version": "v2.10",
                "revision": "r5230+12253-c6f71ad30b",
                "target": "ath79/generic",
                "description": "OpenWrt-8devices v2.10 r5230+12253-c6f71ad30b"

It appears you are using firmware that is not from the official OpenWrt project.

When using forks/offshoots/vendor-specific builds that are "based on OpenWrt", there may be many differences compared to the official versions (hosted by Some of these customizations may fundamentally change the way that OpenWrt works. You might need help from people with specific/specialized knowledge about the firmware you are using, so it is possible that advice you get here may not be useful.

You may find that the best options are:

  1. Install an official version of OpenWrt, if your device is supported (see
  2. Ask for help from the maintainer(s) or user community of the specific firmware that you are using.
  3. Provide the source code for the firmware so that users on this forum can understand how your firmware works (OpenWrt forum users are volunteers, so somebody might look at the code if they have time and are interested in your issue).

If you believe that this specific issue is common to generic/official OpenWrt and/or the maintainers of your build have indicated as such, please feel free to clarify.

Probably worth checking if you still have 3g coverage