3.3 Incremental Zone Transfer

Incremental zone transfer is specified by RFC 1995. Incremental zone transfer (IXFR) enables the transfer of only the data changed from the master server to the slave server, i.e., just a part of the relevant zone, should a change in the zone data occur. On the other hand, the classic zone transfer (AXFR) transfers the whole zone, should it be altered in any way.

The database history is needed in order for the master server to be able to provide the slave server with only the zone records that have been changed. The master server is thus obliged to keep track of the differences between the newest version of the zone and several older ones. The master server sends the zones that have been corrected on the master server by using DNS Update to the slave server via IXFR. Individual file versions differ in the serial number contained in the SOA record. If the slave server finds out that it needs new data for the zone and supports IXRF, it sends a request to the...