Efficacy of using short timeout values for an A record
Chuck Swiger
cswiger at mac.com
Tue Feb 14 18:42:06 UTC 2012
On Feb 14, 2012, at 2:59 AM, goran kent wrote:
> 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 10.10.10.10
>
> 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?
ISC's BIND has (or had) a MINTTL value of 5 minutes / 300 seconds.
It's probably unreasonable to expect other platforms to refetch DNS
records faster than that.
Aside from DNS, you're going to run into layer-2 problems with MAC-to-IP
mappings in your switches if you try to move an IP around at sub-minute
intervals.
What problem are you actually trying to solve? It's likely that a tool
or mechanism like load-balancing onto a pool of boxes would provide a
much better solution than expecting to move a box around so rapidly....
Regards,
--
-Chuck
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