Re: [dhcwg] DDNS-DHCP [6]: Relationship between DNS TTL and DHCP lease length

Bruce Campbell writes:
> So, the next question is, since Client A and Client B received different
> (authoritative) responses, does that mean that there were different
> versions of the zone 'example.com' at time T and T+100 ?

Of course not; that would be silly. The TTD---which is what caches
actually store anyway---is the same. Queries at different times will
interpret the same TTD as different TTLs, of course, but that doesn't
mean the zone has changed.

If you insist on corrupting the zone by retrieving it through AXFR,
you'll get 2-second TTLs from my AXFR server. Of course, the record also
won't disappear until the next AXFR. The effects on the secondary, and
on clients talking to the secondary, are the same as if you had manually
set a 2-second TTL in the first place.

If you transfer the zone accurately (for example, through rsync), the
secondary will allow more caching before the time-to-die than it would
have with a 2-second TTL, and it will remove the record at exactly the
right time without another transfer.

---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago

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