Understanding zones

DNS data is divided into manageable sets of data called zones. Zones contain name and IP address information about one or more parts of a DNS domain. A server that contains all of the information for a zone is the authoritative server for the domain. Sometimes it makes sense to delegate the authority for answering DNS queries for a particular subdomain to another DNS server. In this case, the DNS server for the domain can be configured to refer the subdomain queries to the appropriate server.

For backup and redundancy, zone data is often stored on servers other than the authoritative DNS server. These other servers are called secondary servers, which load zone data from the authoritative server. Configuring secondary servers allows you to balance the demand on servers and also provides a backup in case the primary server goes down. Secondary servers obtain zone data by doing zone transfers from the authoritative server. When a secondary server is initialized, it loads a complete copy of the zone data from the primary server. The secondary server also reloads zone data from the primary server or from other secondaries for that domain when zone data changes.

DNS zone types

You can use iSeries™ DNS to define several types of zones to help you manage DNS data:

Primary zone

Primary zone loads zone data directly from a file on a host. It can contain a subzone, or child zone. It can also contain resource records, such as host, alias (CNAME), address (A), or reverse mapping pointer (PTR) records.

Note: Primary zones are sometimes referred to as master zones in other BIND documentation.

Subzone

A subzone defines a zone within the primary zone. Subzones allow you to organize zone data into manageable pieces.

Child zone

A child zone defines a subzone and delegates responsibility for the subzone data to one or more name servers.

Alias (CNAME)

An alias defines an alternate name for a primary domain name.

Host

A host object maps A and PTR records to a host. Additional resource records can be associated with a host.

Secondary zone

Secondary zone loads zone data from a zone's primary server or another secondary server. It maintains a complete copy of the zone for which it is a secondary.

Stub zone

A stub zone is similar to a secondary zone, but it only transfers the name server (NS) records for that zone.

Forward zone

A forward zone directs all queries for that particular zone to other servers.