On Aug 19 2011, 刘明星：） wrote:
I test BIND 9.7.2-P2 and thus find the ttl for negative responses is
not following rfc2308, and instead check the $TTL. If the TTL is smaller
than 3h, negative ttl is set to the TTL, otherwise to check mimum TTL.
If the value is smaller than 3h, negative ttl is set to the ttl,
otherwise set to 3h(10800)
Why do you say this is "not following RFC 2308"? To quote from that
document (end of section 5)
| As with caching positive responses it is sensible for a resolver to
| limit for how long it will cache a negative response as the protocol
| supports caching for up to 68 years. Such a limit should not be
| greater than that applied to positive answers and preferably be
| tunable. Values of one to three hours have been found to work well
| and would make sensible a default. Values exceeding one day have
| been found to be problematic.
BIND's default cutoff value of 3 hours can be altered by using
max-ncache-ttl option if you need to.
--
Chris Thompson
Email: c...@cam.ac.uk
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