TTL question

Simon Waters Simon at
Mon Oct 8 15:51:51 UTC 2001

"Sasso, John IT" wrote:
> I take it that a TTL now must be explicitly defined?  I heard within this
> list that (in an RFC????) the meaning between the TTL in the SOA record and
> the TTL explicitly defined (a la $TTL) changed in BIND 9.x.  Correct me if
> I'm wrong, but the TTL in the SOA record refers to the negative caching of
> records, whereas the $TTL refers to the "regular" caching of names (i.e.
> non-negative cache).

Spot on - RFC 2308 modified RFC1035.

This isn't specifically a BIND 9 change, but a change to the
standard for the zone file, all nameservers should work this way
if they take standard conforming zone files. This is important
should you ever want to migrate to another DNS server without
resetting all your TTL's.

Obviously it is more important than that, as it allows the
default TTL, and negative cache TTL times, to differ. The
negative cache TTL is bounded by BIND 9 caches to a maximum of 3
hours (by default), I assume other name servers are free to
ignore this restriction.


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