There may also be several secondary or slave servers that have copies of information from the primary, and act as backups in case the master server for the zone is unavailable.
A single DNS server may host multiple zones, or sometimes may not host any at all.
However, some domain authorities require it to be in a certain date-based format, such as YYYYMMDDnn.
Normally a single server hosts either entirely master zones, or entirely slaves.
A server is typically responsible for providing information about the zones that it hosts, and for looking up information in other zones when requested to by DNS clients.
For a zone hosted by a server to be available to DNS clients that do not query that server directly, it must be registered in the parent zone.
The domain name system is divided into zones (also called domains), each of which has a name like or au.
Secondaries can also share the load on the primary server, because other servers looking up records in the domain will randomly choose a server to query instead of always asking the primary first.
In fact, there is no way for other systems to know which server is the master and which are the slaves for a particular zone.
A normal system is only a DNS client, and never has to answer requests from servers.
Almost all companies, organizations and ISPs will already have one or more DNS servers on their network that all the other hosts can use.