Can bind be configured to not drop RR's from the cache when the upstream DNS server is unresponsive

[John Wobus]

On Mar 18, 2016, at 6:28 AM, Barry Margolin <barmar at alum.mit.edu> wrote:
> In article <mailman.384.1458255932.73610.bind-users at lists.isc.org>,
> Mark Andrews <marka at isc.org> wrote:
> 
>> How do you actually expect this to ever work in real life?
> 
> I'm pretty sure Google DNS does this. Other resolver operators often get 
> complaints about "Why can't I look up <whatever> through your DNS 
> servers when I can do it through Google DNS?"

I’d guessed Google just re-queries before it needs to, which has benefits but
requires a more complex “clean out very-seldom-used records” strategy.
I’d imagine they'd use a somewhat-random amount of time to pre-query
as one of their measures against cache poisoning.

This would be a good nameserver feature, e.g. when a response is given
from the cache, a secret (shorter) ttl is adjusted to help assure continuity.
Or other variants.  Such a feature might address Ron’s concern.
(I believe I recall discussions on this or another list, perhaps even
a feature in the wings.)

In any case, I cringe at the thought of overriding TTLs.  They’re there
for a reason.  In some instances, overriding could “help”, but in others, it
would be really, really bad.

John Wobus
Cornell University IT