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

[Barry S. Finkel]

On 3/17/2016  12:36:31 +0100 Ron<ron.arts at gmail.com> wrote:

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

> Hi,
>
> subject says all. Read manpages, could not find this in the FAQ's.
> Hope this is possible. If not does anyone know of other name servers
> that offer this option?
>
> Thanks,
> Ron Arts

It seems to me that one task of the BIND process is periodically
to scan the cache to find entries whose TTL has expired.  That
process, per the DNS RFCs, will remove all entries whose TTL has
expired.  The process should not check to ensure that at least
one of the upstream DNS servers is responsive, as by definition
the record has expired and should not remain in DNS.  It is the
owner of the record who sets the TTL, and if the TTL is too short
AND all of the DNS servers that serve that record are inaccessible,
then the owner of the record has a problem.

--Barry Finkel