Brave Stops Using Internal DNS

Description of the issue:
Several times per week, the Brave Browser stops resolving IPs with the internal DNS server configured in Windows and falls back to the secondary DNS server, which is external. This causes the internal websites to stop being reachable, since they are only accessible from within the LAN using their internal IPs.
To recover so that Brave starts using the internal DNS again I have to set “Use secure DNS” to on and then back to off, or restart the browser. However, when the problem is occurring, if I open a private tab it works as expected: using the internal DNS server.

How can this issue be reproduced?

  1. Have Brave use an internal DNS server.
  2. After a few hours or days Brave stops using it for IP resolution.

Expected result:
Brave keeps using the internal DNS server for IP resolution.

Brave Version( check About Brave):
Version 1.52.126 Chromium: 114.0.5735.133 (Official Build) (64-bit)

Additional Information:
The internal DNS server does not use secure DNS. “Use secure DNS” is disabled in the Brave settings.
This problem started months ago, after years of using the same setup without issues. I see it on the two machines where I use Brave. Chrome and Firefox are not affected by this.
I suspect that for some reason Brave at some point thinks that the internal DNS server is down and therefore goes to the secondary server. So, the question is what kind of check is Brave doing to see if the DNS server is alive. Interestingly, Chrome and Firefox run continuously without having this issue, despite surely having a similar mechanism to probe for DNS reachability.

Have to ask, are Chrome and Firefox definitely using the same resolver(s)? They are not doing ‘Secure DNS’ or DoH?

I get that they are still able to resolve ‘internal’ names but that could be incidental depending on how those names are defined and how they’re being resolved.

Positive. All browsers are set the use system settings, which are DHCP.
From the LAN it’s impossible get to the internal sites without asking the internal DNS server because I’m using split DNS: internal DNS resolves the internal IP, but outside the network public DNS servers return my external IP.
When Brave switches to external DNS it gets my external IP, which won’t work because by design on this network you can’t use the external IP to access internal services from the LAN (NAT hairpinning is not configured).

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