Configuring different TTLs in multiple RRs for the same domain name, TYPE, and CLASS

Dave Warren davew at
Thu Mar 24 22:04:45 UTC 2016

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?

Dave Warren

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