Zone transfer formats

Some name server implementations have the capability to send multiple resource records in a DNS message during a zone transfer operation, instead of just one resource record per DNS message. The process of sending multiple resource records per DNS message is described in RFC 2671, Extension Mechanisms for DNS (EDNS0). For information about accessing RFCs, see Related protocol specifications.

Sending multiple resource records per DNS message is more efficient than sending just one. ADNR performs zone transfer requests from the name servers it manages. ADNR supports receiving zone transfers in either format, but is more efficient at processing the format that contains multiple resource records per DNS message.

The BIND 9 name server sends multiple resource records per DNS message by default. However, some name server implementations do not support receiving zone transfers using this format. For this reason, some name servers might be configured to use the less efficient format when sending zone data to a secondary name server. The BIND 9 name server supports specification of the zone transfer format on the transfer-format option. This option can be specified on a server statement, which can be used to set the option only when sending zone transfer information to ADNR, so that other name servers are unaffected by the setting.