Cache Entries
Kevin Darcy
kcd at daimlerchrysler.com
Wed Apr 18 00:55:05 UTC 2007
Robert Spangler wrote:
> Hello,
>
> A question has been raised about TTL and cached entries. After the first
> request do the following request reset the cache TTL or does the entry
> continue to count down until it expires and once it reaches zero the cache is
> is cleared until the next request which starts the process all over again?
>
Once an answer is cached, you answer from the cache until the TTL
expires, at which point you go and fetch a fresh set of records. The
only way I could see the TTL being "reset" is if the same data was seen
in a response to some other query (e.g. part of a CNAME chain) that is
of equal or higher credibility/trustworthiness/rank (a la RFC 2181).
Then maybe the new data would "refresh" the old cache TTLs. But I
haven't actually tested this in practice. Modern BINDs have a lot of
protection against cache poisoning, so it's possible that such
"refreshes" will no longer occur.
- Kevin
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