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List:       ipng
Subject:    Extremely long TTLs
From:       "D. J. Bernstein" <djb () cr ! yp ! to>
Date:       2001-01-26 19:18:52
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Christian Huitema writes:
> information that does not change, such as the lower bits of a node's
> address, can be stored with a longer TTL than the site's prefix.

Everything changes. Machines acquire extra IP addresses. Machines
disappear. Even MAC addresses change: network cards die. (It isn't
always possible, never mind easy, to reprogram the MAC address on the
new card.)

Those of us who write caches don't want to deal with users asking ``why
am I getting the old address?'' when a novice administrator starts with
a silly 6-week TTL and then suddenly realizes that he has to change the
address. My cache never saves data for more than a week.

Yes, TTLs vary. Yes, some fraction of queries will be saved by longer
TTLs. But every record, no matter how stable, will be refreshed
periodically. A careful analysis takes all of this into account.

---Dan
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