What is a DNS zone transfer?
A DNS zone transfer is a type of DNS transaction you can implement. With a DNS zone transfer, primary and secondary DNS servers can exchange zones with each other, including all resource records, which is a critical requirement for redundancy and backup for DNS data. DNS zone transfers are usually done to replicate DNS data to a number of different DNS servers. It can also distribute DNS updates and changes across multiple servers.
Usually, records from the primary DNS server are shared with secondary and other DNS servers during a DNS zone transfer. A DNS zone transfer is usually a very long and time-consuming process, so organizations started implementing incremental DNS zones, which transfer only the changes since the previous transfers to speed up the process and save time.
See also: DNS filtering, DNS server, DNS MX record, DNS SOA record
How do DNS zone transfers work?
DNS zone transfers are the process of copying DNS records from a primary DNS server to a secondary server to ensure consistency. There are two types of zone transfers: full zone transfers (AXFR), which replicate the entire zone file, and incremental zone transfers (IXFR), which only update changes since the last transfer. AXFR is typically used when setting up a secondary DNS server, while IXFR is more efficient for ongoing updates, reducing bandwidth by only transferring modified records. These transfers help maintain DNS redundancy and improve reliability across networks.
DNS zone transfer records
SOA record. The DNS start of authority (SOA) record is a mandatory DNS record and serves as the starting point for a DNS zone. It contains information like the name of the server, the name of the administrator of the DNS zone, the current SOA record version, the amount of time (in seconds) that a secondary DNS server needs to wait before checking for updates, and the amount of time (in seconds) to wait before trying a failed transfer again. Its purpose is to indicate the authoritative DNS server for the zone, manage zone parameters, and facilitate zone transfer.
MX record. The MX (mail exchange) record determines which mail server must accept email messages on behalf of a domain name. It allows email to be routed correctly by specifying the priority of multiple mail servers for a domain.
TXT record. The TXT (text) record allows you to associate arbitrary text with names or a host. It can contain valuable information, like data center information, domain ownership verification, network information, and other account information.
Why is DNS zone transfer important?
DNS zone transfers are important for maintaining the availability, redundancy, and consistency of DNS records across multiple servers. By copying DNS data from a primary server to secondary servers, zone transfers ensure that if the primary server goes down, secondary servers can continue to resolve domain queries.
