D. J. Bernstein <djb(_at_)cr(_dot_)yp(_dot_)to> schrieb/wrote:
A moment ago we were being told how vitally important it was for AXFR
clients to preserve all records received under all circumstances:
* ``An ACURATE [sic] copy of the zone is ESSENTIAL'';
* ``A modified zone is NOT a [sic] ACURATE [sic] copy. It's not
even a copy. It is a derived work'';
Well, djb raises an intersting question here: Is that really necessary?
Or, even one step further: Is it necessary that all authorative servers
have the same SOA record for a zone, especially the serial number?
I think the only requirement that's really essential is that the serial
number changes whenever the data that would be returned by a zone
transfer changes (even if that breaks database consistency for the SOA
record's serial number).
One strategy to implement this would be to keep an exact copy of a zone
obtained from other servers for outgoing transfers (so you'll always use
the original serial number), which is the BIND 9 strategy.
Another strategy would be to just increment the serial number of a zone
when it is actually changed by importing glue records from another zone.
This would solve the synchronisation problem, too: If the parent zone is
updated too early, the server might throw away the glue record. But it
will update the parent zone and increase its the serial number when it
gets an up-to-date copy of the child zone.
Claus
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