On 2016-03-24 15:20, Tony Finch wrote:
Dave Warren <da...@hireahit.com> wrote:
On 2016-03-24 09:46, Ray Bellis wrote:
On 24/03/2016 16:41, Tony Finch wrote:
When I changed our TTLs from 24h to 1h last year, it didn't have a visible
effect on authoritative server query load, much to my surprise.
I'm not that surprised - there's definitely not a linear correlation
between the TTL of an RRset and how frequently it's queried.
Unless your TTL is very short, forced expulsion from cache (due to
cache-size limits) would cause many clients to re-query for a record far
more frequently than once-per-TTL.
Has anyone ever done any evaluation on this? For average resolvers, what
is the longest TTL that has any utility?
There was a great paper published 15 years ago describing a study of DNS
cache effectiveness at MIT. http://nms.csail.mit.edu/projects/dns/
It concluded (amongst other things) that NS records (and associated
address records) are really important, but leaf records that users ask for
don't matter so much. (Based on cache hits before TTL expiry, IIRC.)
I don't know of a similar study performed more recently.
The internet was a very different place 15 years ago, in particular,
this was before every Windows client machine had it's own DNS cache
service and largely before today's connected mobile devices were a thing.
I'm not sure how mobile devices cache, in particular, whether they clear
their cache when moving between connections or not (although I suspect
yes, otherwise there would be more issues with split DNS environments)
My gut feeling is that the findings wouldn't be all that different in
the end anyway.
https://00f.net/2012/05/10/distribution-of-dns-ttls/ is also interesting.
Definitely an interesting read, thanks!
--
Dave Warren
http://www.hireahit.com/
http://ca.linkedin.com/in/davejwarren
_______________________________________________
Please visit https://lists.isc.org/mailman/listinfo/bind-users to unsubscribe
from this list
bind-users mailing list
bind-users@lists.isc.org
https://lists.isc.org/mailman/listinfo/bind-users
