getaddrinfo consistently fails when connected with Proximus NB-IoT with proximus sim card, or Telenet NB-IoT with Telenet sim card.

[Sebastiaan Merckx]

Hi,

I have used an NRF9160 in Belgium with the iBasis sim card, connecting via LTE-M and NB-IoT with operators Orange and Proximus. HTTP requests work fine.

However, when using a dedicated Proximus sim card (which has been used for another project in another MCU+modem [pycom]), getaddrinfo fails consistently in NB-IoT mode, returning random error values. Retries don't help. The strange thing is that the modem returns a "CSCON: 0" AT notification! Proximus requires a specific APN to be configured with this sim card (m2minternet.proximus.be) which is not required when using the iBasis sim card, that is the only difference in the code compared to using iBasis sim card.

Something similar is observed with a dedicated Telenet sim card on the NB-IoT Telenet network: the getaddrinfo here returns -11 (DNS_EAI_SYSTEM). I am just trying to resolve google.com. When using a direct IP address like 142.250.179.174, the getaddrinfo works fine and a HTTP HEAD request is returned. So for telenet, the connection itself works fine but the DNS does not seem to be working. Note that here we also use a dedicated APN (iot.telenet.be).

What could be the root cause of these issues?

[Sebastiaan Merckx]

In the meanwhile I understood from Pycom releases (https://forum.pycom.io/topic/4247/dns-now-working-a-list-documentation-of-all-lte-nb1-nb-iot-lte-m-lte-catm1-operators-around-the-world?_=1637660062751) that DNS is not implemented by default by the operator.

Pycom has created a solution for that by manually setting the DNS servers (see link). How should this be handled on NRF9160? Do we need to code the DNS lookups ourselves?

What could be the reason that all of this works fine with iBasis SIM card and default APN, and does not work when using specific operator sim cards?

[Sebastiaan Merckx]

I have only now found similar tickets (https://devzone.nordicsemi.com/f/nordic-q-a/50029/nrf9160-modem-firmware-v1-0-0-setting-custom-dns-server and https://devzone.nordicsemi.com/f/nordic-q-a/44294/using-getaddrinfo-for-dns-lookups-nrf9160-dk ) but they don't help me much since nrf_setdnsaddr does not seem implemented anymore.

Or should we use dns_resolve_init() ?

[Sebastiaan Merckx]

I got help from a Nordic employee who suggested to fall back to PCO instead of EPCO, with AT command

at_cmd_write("AT%XEPCO=0", NULL, 0, NULL);

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