[FS#391] dnsmasq stops working properly if the fastest upstream DNS server returns a server failure

[LEDE Bugs]

The following task has a new comment added:

FS#391 - dnsmasq stops working properly if the fastest upstream DNS server returns a server failure
User who did this - Baptiste Jonglez (bjonglez)

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Did it start happening after the update to dnsmasq 2.76, in May 2016?

These commits look relevant:

http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commitdiff;h=51967f9807665dae403f1497b827165c5fa1084b (introduced in dnsmasq 2.69)
http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commitdiff;h=4ace25c5d6c30949be9171ff1c524b2139b989d3 (introduced in dnsmasq 2.76)

So, the first commit introduced the issue you see as a "feature" (but there was a bug in the implementation, so it didn't work), while the second commit made the first commit actually work starting from dnsmasq 2.76.

I'm not sure what is the right behaviour, but it indeed sounds strange to treat SERVFAIL as a valid response.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=391#comment1282