Technical data

are easier to keep track of if they are short. The sum of all the label characters
and label lengths cannot exceed 255.
_________________________ Note _________________________
Domain names are not case sensitive. However, the case of entered
names is preserved whenever possible.
For example, the fully qualified domain name
euro.sales.compaq.com
is broken
down as follows (from right to left):
•The
com
label refers to the commercial top-level domain.
•The
compaq
label refers to the
compaq
domain, a subdomain of the commercial
domain.
•The
sales
label refers to the
sales
domain, a subdomain of the compaq
domain.
•The
euro
label refers to the host called
euro
, a subdomain of the
sales
domain.
8.5 Zones
For management reasons, a domain can be divided into zones, which are discrete,
nonoverlapping subsets of the domain. A zone usually represents an administrative
or geographic boundary, and authority for the zone may or may not be delegated to
another responsible group or person. Each zone starts at a designated level in the
domain name tree and extends down to the leaf domains (individual host names) or
to a point in the tree where authority has been delegated to another domain.
A common zone is a second-level domain, such as
abc.com
. Many second-level
domains divide their zones into smaller zones. For example, a university might
divide its domain name space into zones based on departments. A company might
divide its domain name space into zones based on branch offices or internal
divisions. Authority for the zone is generally delegated to the department or
branch office. The department or branch office then has the responsibility for
maintaining the zone data.
All the data for the zone is stored on the master server in zone files.
8.5.1 Delegation
When a zone is very large and difficult to manage, authority for a portion of the
zone can be delegated to another server; the responsibility for maintaining the zone
information is also delegated.
For example, the
edu
zone contains many educational organizations. Each
organization is delegated the authority for managing their portion of the
edu
zone,
thereby creating subzones. For example, both
rpi.edu
and
uml.edu
are subzones
of the
edu
zone and each organization has the responsibility for maintaining the
zone information and the master and slave servers for their respective zones.
8.6 Reverse Domains
The Internet has a special domain used for locating gateways and supporting
internet address-to-host name lookups. The mapping of internet addresses to
domain names is called reverse translation. The special domain for reverse
translation is the IN-ADDR.ARPA domain.
8–4 Domain Name System/BIND (DNS/BIND)