[RndTbl] programatically determine if DNS is down or blocked?

[Hartmut W Sager]

But obviously, no number of local parameters can dictate what happens to
DNS resolving beyond your local infrastructure (LAN).  Even if there were
parameters that "suggest" behaviour to upstream servers, those servers
could ignore that.  I suspect that full zone file retrieval (or full zone
file content retrieval) commands might be the only way to be sure that
caching is bypassed.

Hartmut W Sager - Tel +1-204-339-8331, +1-204-515-1701, +1-204-515-1700,
+1-810-471-4600, +1-909-361-6005


On 7 April 2016 at 07:51, wyatt at prairieturtle.ca <wyatt at prairieturtle.ca>
wrote:

> dig has parameters to force cache bypass.
>
> Daryl
>
> ----- Reply message -----
> From: "Trevor Cordes" <trevor at tecnopolis.ca>
> To: "Robert Keizer" <robert at keizer.ca>
> Cc: "Continuation of Round Table discussion" <roundtable at muug.mb.ca>
> Subject: [RndTbl] programatically determine if DNS is down or blocked?
> Date: Wed, Apr 6, 2016 15:41
>
> On 2016-04-06 Robert Keizer wrote:
> > Why don't you use dig+grep+sed in bash?
>
> Ya, that's one of the ideas (dig).  It looks like dig will
> differentiate between named down, vs blocked 53, vs simple invalid
> domain.
>
> I'm trying to see if there are other ways also, perhaps ones that don't
> require a fork.  And the dig will send out real queries to real
> servers, but I guess it will be tempered by the cache?  I'll have to
> test what dig does in the different failure modes when a) resolving a
> domain that isn't cached vs b) resolving one that is cached.
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