DNS on Windows Server 2003, 3rd Edition

Types of Name Servers

The DNS specs define two types of name servers: primary masters and secondaries. A primary master name server for a zone reads the data for the zone from a file on its host. A secondary name server for a zone gets the zone data from another name server authoritative for the zone, called its master server. Quite often, the master server is the zone’s primary master, but that’s not required: a secondary can load zone data from another secondary. When a secondary starts up, it contacts its master name server and, if necessary, pulls the zone data over. This is referred to as a zone transfer. Nowadays, the preferred term for a secondary name server is a slave, though many people (and some software, including Microsoft’s DNS console) still use the old term.

Both the primary master and secondary name servers for a zone are authoritative for that zone. Despite the somewhat disparaging name, secondaries aren’t second-class name servers. DNS provides these two types of name servers to make administration easier. Once you’ve created the data for your zone and set up a primary master name server, you don’t need to copy that data from host to host to create new name servers for the zone. You simply set up secondary name servers that load their data from the primary master for the zone. The secondaries you set up will transfer new zone data when necessary.

Secondary name servers are important because it’s a good idea to set up more than one authoritative name server ...