Introduction to DNS

Full Zone Transfer

In a full zone transfer, defined in the original DNS specifications, the master server for a zone transmits the entire zone database to the secondary server for that zone. Secondary servers initiate full zone transfers using the following process:

The secondary server for the zone waits a certain amount of time (specified in the Refresh field of the SOA resource record), and then polls the master server for its SOA.
The master server for the zone responds with the SOA resource record.
The secondary server for the zone compares the returned serial number to its own serial number. If the serial number sent by the master server for the zone is higher than its own serial number, that means its zone database is out of date, and it sends an AXFR request (a request for a full zone transfer).
The master server for the zone sends the full zone database to the secondary server.

If the master server for the zone does not respond to polling by the secondary server, the secondary server continues to retry after the interval specified in the Retry field of the SOA resource record. If there is still no answer after the interval specified in the Expire field since the last successful zone transfer, it discards its zone.

Note

Name servers running versions of BIND earlier than 4.9.4 can send and receive only one resource record per message during a full zone transfer. Name servers running versions of BIND 4.9.4 and later, and Windows 2000, can send and receive multiple resource records per message. This improves the performance of full zone transfers.

However, to provide backward compatibility, name servers running Windows 2000 default to sending only one resource record per message if any secondary servers that are not running Windows are configured for the zone. If you have secondary name servers running versions of BIND 4.9.4 and later, configuring Windows 2000 to send multiple resource records per message improves performance. For more information, see the link to the Microsoft TechNet Web site on the Web Resources page at http://windows.microsoft.com/windows2000/reskit/webresources. On the TechNet Web site, search for "DNS Compatibility," "BIND," and "4.9.4."