BIND and UDP tuning

Alex mysqlstudent at
Thu Sep 27 16:03:34 UTC 2018


> On Thu, Sep 27, 2018 at 10:53:25AM -0400, Alex wrote:
> > Many of these values I've already tweaked and have had no effect on my
> > SERVFAIL issues :-(
> If you are getting SERVFAILs from a BIND resolver you administer, then
> it has responded to your query. If you turn up the log level to
> something like -d 99, it'll print the steps that led to that SERVFAIL.
> Usually you'll find something there that directs you to next steps.
> On this topic, my home resolver is also a stock packaged BIND version as
> you, and I too see spurious SERVFAILs sometimes. I used to think this
> was due to too much indirection, e.g., when named starts up and you run:
>     dig -x

It doesn't typically happen when running from the command-line. It
does occasionally happen, though. I usually run something like "dig
+all +trace +nodnssec <hostname>". It sometimes times out in the
middle, with something like "cannot resolve xyz host", which may even
be one of the root servers.

I also typically run it with "rndc trace 11" which shows me quite a
bit of debugging info - too much to look through manually. With trace
99, I can imagine it being overwhelming amount of info. Do you have
any ideas of what to look for? "query-errors"?

Also, I also see other SERVFAIL errors that really are SERVFAIL errors
- when querying the host manually, it still responds immediately with


> on a cold cache. However it seems to be returning SERVFAIL sometimes for
> what should be a cached answer. I'll also turn up the debug logging and
> watch it.
>                 Mukund

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