nRF9160 DNS cache & TTL

RE: nRF9160 DNS cache & TTL

Sebastiaan Merckx — Thu, 02 Oct 2025 09:56:35 GMT

Okay, good to know, thanks.

What we could also see in pcap captures is that the NRF91 performs an IPV6 DNS request and gets a response with only CNAME record, and it does not perform an IPV4 DNS request. This might be an indication that the modem implementation mixes IPV6 and IPV4 responses, which is wrong.

But we've just done some IPV4-only tests where the same (or similar?) issue occurs - we still need to look at the captures. I haven't activated modem traces yet.

RE: nRF9160 DNS cache & TTL

Stephan Walter — Thu, 02 Oct 2025 08:49:38 GMT

Hi Sebastiaan, our problem was with Vodafone as well. Unfortunately I don't know how the problem ultimately got resolved, if at all. A workaround would be to add the IP addresses to the whitelist instead of the FQDN. Of course that defeats the advantages of a domain name.

RE: nRF9160 DNS cache & TTL

Sebastiaan Merckx — Thu, 02 Oct 2025 08:28:25 GMT

Hi Stephan Walter ,

Which provider are you talking about? I'm facing similar issues with Vodafone.

Did you manage to solve this issue?

Kind regards,

Sebastiaan

RE: nRF9160 DNS cache & TTL

Stephan Walter — Wed, 17 Apr 2024 06:13:00 GMT

Hi Håkon,

Thanks for your help. We have run a test with tracing enabled (NRF_MODEM_LIB_TRACE_LEVEL_IP_ONLY), and it looks like the nRF91 indeed handles the TTL correctly. Still it would be nice to have some way to influence the DNS cache on the nRF91.

We suspect that our provider hasn't implemented the TTL in the firewall correctly.

RE: nRF9160 DNS cache & TTL

Håkon Alseth — Tue, 19 Mar 2024 13:10:51 GMT

Hi,

I got confirmation from R&D.

[quote user=""]Is it correct that the nRF91 caches DNS responses for longer than the TTL permits?[/quote]

We have a internal test on this, and this is not failing, meaning that we observe that the nRF9160 modem fw is not caching longer than TTL permits.

[quote user=""]Is there a way to change this behavior and force it to respect the TTL?[/quote]

Could you please share a modem trace showing this behavior?

[quote user=""]Is there a way to disable, clear, or dump the DNS cache?[/quote]

Unfortunately, no. There is no way to clear the DNS cache.

Kind regards,

Håkon

RE: nRF9160 DNS cache & TTL

Håkon Alseth — Mon, 18 Mar 2024 15:01:07 GMT

Hi,

I can confirm that the nRF9160 does cache DNS lookups, but I do not have details related to the below questions (yet):

[quote user=""]

Is it correct that the nRF91 caches DNS responses for longer than the TTL permits?

Is there a way to change this behavior and force it to respect the TTL?

Is there a way to disable, clear, or dump the DNS cache?

[/quote]

I'll ask R&D about these specific questions and get back to you within a few business days.

Kind regards,

Håkon