19.5.1. DNS Protocol Enhancements
BIND supports Incremental Zone Transfers (IXFR), where a slave nameserver only downloads the updated portions of a zone modified on a master nameserver. The standard transfer process requires that the entire zone be transferred to each slave nameserver for even the smallest change. For very popular domains with very lengthy zone files and many slave nameservers, IXFR makes the notification and update process much less resource-intensive.
Note that IXFR is only available when using dynamic updating
to make changes to master zone records. If manually editing zone files to make changes, Automatic Zone Transfer (AXFR) is used. More information on dynamic updating is available in the BIND 9 Administrator Reference Manual
referenced in Section 19.7.1, “Installed Documentation”