IXFR zone transfer

[Evan Hunt]

> However (and I think this is what you are asking), IXFR is not 
> possible without the journal, and the journal is created by dynamic 
> update. Both master and slave should then fall back to AXFR.

See also the ixfr-from-differences option.  If the master is using
that--and if it's cautiously maintained, always using "rndc reload"
or "rndc reconfig" to load zone changes, instead of killing and
restarting the server--then named can generate a diff between old
and new versions of the zone and generate a journal file, just
as if it had been changed with a dynamic update, and can then
use IXFR with slaves.

-- 
Evan Hunt -- each at isc.org
Internet Systems Consortium, Inc.