Technical data

• Controlling the assignments of the host and domain names
The domain administrator furnishes users with access to names and name-related
information both inside and outside the local domain.
8.4 Domain Names
The InterNIC assigns names for all top-level domains as well as domains directly
below the top-level domains. Individuals are responsible for assigning lower-level
domains and host names.
Each domain has a label. For example, the label for the top-level domain for
commercial organizations is
com
. A label is unique within its parent domain.
The concatenation of all the domain labels from the top-level domain to the
lowest-level domains is called a fully qualified domain name. The labels are
listed from right to left and are separated by dots. For example, the domain name
for a subdomain within the
com
domain would be
abc.com
;
abc
is the label for the
ABC company’s subdomain, and
com
is the label for the commercial domain. This
structure allows administration and data maintenance to be delegated down the
hierarchical tree.
_________________________ Note _________________________
The term domain name is sometimes used to refer to a specific domain
label. The name of the root domain of the name space is a dot (.).
8.4.1 Types of Domain Names
There are two types of domain names: the fully qualified name and the relative
name.
• The fully qualified name represents the complete domain name. This is also
known as the absolute or canonical name. For example:
boston.cities.compaq.com
A domain name that is fully qualified is absolute. You should not append
further BIND extensions to the name.
• The relative name represents the starting name (label) of an absolute domain
name. Relative names are incomplete but are completed by the BIND
service using knowledge of the local domain. Relative host names, such as
boston.cities
, are automatically expanded to the fully qualified domain
name when given in a typical command.
8.4.2 Domain Name Format
The format of domain and host labels have the following characteristics::
• Contains characters, digits, or a hyphen.
• Must begin with a character or digit.
• Must not end with a hyphen.
• Has a maximum of 63 characters for each label.
• Has a maximum of 255 characters in a fully qualified domain name.
Although label names can contain up to 63 characters, it is best to choose names
that are 12 characters or less because the canonical (fully qualified) domain names
Domain Name System/BIND (DNS/BIND) 8–3