Override default DNS on FX30S GENERIC LTE GENERIC M/NB IoT

gianpaolo · December 7, 2021, 7:16am

Hi
I am trying to override the default DNS given by the SIM carrier, after downloading Legato R14 with framework version 18.09.02 and after some search , i found that the legato framework does not set any dns , it just read them and populate the resolv.conf in the linux subsystem.
After some experiment i managed to override the DNS that the legato framework retrieve from the connection so the DNS in the resolv.conf are always google dns.
However the cm data command always returns the SIM Carrier DNS.
Where does the CM DATA command retrive those DNS?
Going deeper i found something about PPP protocol , and an argument called “usepeerdns” but modifying this argument does not give any difference once i build the legato cwe.

Any suggestion?

Thanks

jyijyi · December 7, 2021, 8:04am

for the “cm data” script, you can see:

github.com

legatoproject/legato-af/blob/master/apps/tools/scripts/cm

#!/bin/sh

################################################################################
#                                                                              #
# cm is a shell script that wraps the cm binary in order to start a data       #
# session based on cellular modem technology. It sets up the last registered   #
# profile preferences, the ip routing table and tests the connection (just a   #
# ping test to see if we can reach the outside world).                         #
#                                                                              #
# For more information type 'cm help'.                                         #
#                                                                              #
# Copyright (C) Sierra Wireless Inc.                                           #
#                                                                              #
################################################################################

CM=${CM:="/legato/systems/current/apps/tools/read-only/bin/cm"}
IP=${IP:="/sbin/ip"}
IFCONFIG=${IFCONFIG:="/sbin/ifconfig"}
RESOLV_CONF=${RESOLV_CONF="/etc/resolv.conf"}
LOG=${LOG:="/var/log/cm"}

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I think the DNS is retrieved by le_mdc_GetIPv4DNSAddresses()

github.com

legatoproject/legato-af/blob/master/apps/tools/cm/cm_data.c

//-------------------------------------------------------------------------------------------------
/**
 * @file cm_data.c
 *
 * Handle data connection control related functionality
 *
 * Copyright (C) Sierra Wireless Inc.
 */
//-------------------------------------------------------------------------------------------------

#include "legato.h"
#include "interfaces.h"
#include "cm_data.h"
#include "cm_common.h"
#include "dcs_utils.h"

static char ConfigTreeRoot[LE_CFG_STR_LEN_BYTES] = {};
static void ResetSessionCleanup(void);

//--------------------------------------------------------------------------------------------------

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gianpaolo · January 7, 2022, 10:35am

Hey , sorry for being late, but , thanks for the hint on the "cm data " script , in the end i’ve successfully rebuilt the legato framework with the DNS override following this thread i’ve found :

Topic		Replies	Views
Connection manager FX30	1	734	July 12, 2018
Fx30s Auto CM data connect IoT Gateways	6	200	December 8, 2023
FX30 Connected, losing name resolution FX30	8	132	February 27, 2024
FX30s - Having problem resolving DNS address FX30	8	1242	May 1, 2019
Change ecm network interface FX30	3	405	April 3, 2023

Override default DNS on FX30S GENERIC LTE GENERIC M/NB IoT

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