Learning Windows Server 2003

Using Primary and Secondary Nameservers

DNS has built-in redundancy by having multiple primary and secondary nameservers for a particular domain or zone. Each server, whether identified as primary or secondary, holds a copy of the zone file and acts on its contents. Secondary nameservers can answer queries without limitation from clients, just as primary nameservers can. However, the secondary nameservers must retrieve updates to zones from the primary nameserver on a regular basis to ensure their records are up-to-date.

Each zone can have only one primary nameserver, but can have as many secondary nameservers as is practical. All changes, deletions, and other modifications to a zone are made on the primary nameserver. However, nameservers designated as secondary nameservers hold read-only copies of the zone contents from their associated primary nameservers—zones can’t be directly modified on secondary nameservers. The secondary nameserver automatically will know the primary nameserver for a zone by examining the SOA records for that zone and will contact that machine on a regular basis to force a zone file refresh.

Tip

Secondary nameservers are not limited to zone transfers from only a primary nameserver; they can accept transfers from other secondary nameservers as well.

Several mechanisms exist to force a zone transfer. For one, all of the secondary nameservers will query the primary nameserver for updates: these refreshes are generally “pull"-style updates, whereby machines ...