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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