[dns-operations] TTL=0

Matthew Pounsett matt at conundrum.com
Sun Jan 20 19:27:32 UTC 2019

On Sat, 19 Jan 2019 at 13:16, m3047 <m3047 at m3047.net> wrote:

> Andrew, I don't think that RFC addresses the problem.

I would go back to 1035.

TTL             a 32 bit signed integer that specifies the time interval
                that the resource record may be cached before the source
                of the information should again be consulted.  Zero
                values are interpreted to mean that the RR can only be
                used for the transaction in progress, and should not be
                cached.  For example, SOA records are always distributed
                with a zero TTL to prohibit caching.  Zero values can
                also be used for extremely volatile data.

For the moment, ignoring the case where an authoritative server answer with
TTL=0... say for the sake of argument it responds with TTL=1.  The caching
server should cache it for one second, and after one second should remove
it from the cache.  Therefore, it should never respond from cache with a
TTL of 0.
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