At Sat, 2 Dec 2017 20:09:25 +0530,
Mukund Sivaraman <m...@isc.org> wrote:
> > Strictly speaking yes, it is the same as when a Secondary does not update
> > the zone for a long time.
>
> An authoritiative server operator knows what the consequence of setting
> SOA RDATA fields is. It isn't the same as a cache extending TTL as it
> sees fit, in spite of the loose coherency among primary and secondaries.
>
> I don't agree a downstream cache has authoritiative say about extending
> TTLs (except exceptional circumstances where the authority is
> unreachable ~serve-stale).
+1. I'd accept some level of liberty that an implementation can take,
such as ISC BIND 9 extending a 0-TTL of glue to 1 second:
/*
* Glue with 0 TTL causes problems. We force the TTL to
* 1 second to prevent this.
*/
if (rdataset->ttl == 0)
rdataset->ttl = 1;
but it should be limited to a quite small range. How much is
acceptable may be debatable, but I wouldn't consider "Stretching TTL
from 1 Hour [...] for 10% or 10 minutes" to be acceptable at the
discretion of an implementation.
--
JINMEI, Tatuya
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