In message
<CABLsOLD-KM6DnR8HvfGH8N1M=1bZ4z8zus0YDczaXSfocBQ+Bw(_at_)mail(_dot_)gmail(_dot_)com>
, John Tamplin writes:
On Sun, Jul 24, 2011 at 8:46 PM, Mark Andrews <marka(_at_)isc(_dot_)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: marka(_at_)isc(_dot_)org
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