Incremental Zone Transfer (IXFR)

AXFR is heavy for a frequently updated zone
wrt server load, network bandwidth
IXFR: the solution
RFC1995
primary server keeps update history (journal file)
secondary notifies the primary of the zone's serial number it has
primary only sends diffs to the latest data
No need for specific configuration
IXFR is enabled by default and is used when necessary