In message <CABLsOLD-KM6DnR8HvfGH8N1M=1bz4z8zus0ydczaxsfocbq...@mail.gmail.com>
, John Tamplin writes:
> 
> On Sun, Jul 24, 2011 at 8:46 PM, Mark Andrews <ma...@isc.org> wrote:
> 
> > Adding a SRV lookup should add 0ms if it isn't there as you should be
> > making A, AAAA and SRV lookups in parallel.  Non-existance is as
> > cachable as existance is.
> 
> But you have to wait until the SRV returns even if the A/AAAA response comes
> back first, so there is a non-zero cost even with an optimal implementation.
> I am not arguing whether the cost is worth the benefits, only that there is
> a cost in any case.

In 99.9999% of cases the three answers will come in within 1ms of
each other and you may be waiting on the A or AAAA record.  It
really doesn't take any longer to answer a SRV query compared to a
A or AAAA query.

Mark
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: ma...@isc.org
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