The domain namespace
is divided into areas called zones that are points of delegation in the DNS
tree. A zone contains all domains from a certain point downward, except those
for which other zones are authoritative.
A zone usually has
an authoritative nameserver, often more than one. In an organization, you can
have many nameservers, but Internet clients can query only those that the root
nameservers know. The other nameservers answer internal queries only.
company registered its domain, example.com. It established three
zones—example.com, marketing.example.com, and finance.example.com. ExampleCo
delegated authority for marketing.example.com and finance.example.com to the
DNS servers in the Marketing and Finance groups in the company. If someone
queries example.com about hosts in marketing.example.com, example.com directs
the query to the marketing.example.com nameserver.
In the image below,
the domain example.com includes three zones, with the example.com zone being
authoritative only for itself.
Figure 4. Example.com With Delegated Subdomains
choose not to delegate authority to its subdomains. In that situation, the
example.com domain is a zone that is authoritative for the subdomains for
marketing and finance. The example.com server answers all outside queries about
marketing and finance.
As you begin to
configure zones by using Cisco Prime
Network Registrar, you must configure a nameserver for each zone.
Each zone has one primary server, which loads the zone contents from a local
configuration database. Each zone can also have any number of secondary
servers, which load the zone contents by fetching the data from the primary
server. The image below shows a configuration with one secondary server.
Figure 5. Primary and Secondary Servers for Zones