Efficacy of using short timeout values for an A record

Chris Buxton chris.p.buxton at gmail.com
Tue Feb 14 19:21:19 UTC 2012

Mac OS X imposes a 60 second minimum on TTLs, or at least it did at one time. I am unaware of any other client OS having such a restriction.

Client software does not always respect TTLs, though. It's entirely possible for a client application to completely ignore the TTL value and continue to connect (and reconnect as needed) to whatever address was first retrieved via the stub resolver.

Chris Buxton
BlueCat Networks

On Feb 14, 2012, at 2:59 AM, goran kent wrote:

> Hi,
> I need to setup an A record for a machine who's IP might change
> unexpectedly, and I need to ensure PCs out there cache it for as short
> a time as possible:
>    host1    300  IN A
> Does anyone know whether MS windows PCs will in fact honour that 300s,
> then force a re-lookup?  Can I use even shorter values?  eg, 60?
> I know this will lead to extra DNS traffic, but this is only for this
> particular case.
> Thanks for any comments.
> Regards
> gk
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