The Domain Name System
By Pauline M. Berry
The internet sees the 32 bit IP address to communicate between hosts. However,
users prefer to use computer names rather than numbers. Thus, the domain name
system (DNS) evolved to map names onto addresses. Initially the maintenance of
this mapping facility was performed using a central table. As the internet
became larger and more complex this task became unmanageable. Now a distributed
service exits which has a hierarchy of organised name (the internet name
space). So basically a domain is an administrative entity that allows the
distributed management of host naming. A domain is not the same as a Network! A
network is a physical entity, a domain is an administrative concept and doesn't
necessarily correspond to a network.
The figure below shows how the a sample domain tree looks. A particular
domain is identified by its domain name. A particular hosts name is the list
of nodes on the path from the host's node to the root. For example, the general
form is:
- a computer's name: somewhere.domain (arran.dis.strath.ac.uk)
- a person's e-mail address: user@domain (pb@dis.strath.ac.uk)
The top level domains are mainly countries. However, there are 7 top level
domains not based on a country these are mostly US domains:
- COM
- US Commercial: for businesses and organisations that make a profit through sales of a product or service
- EDU
- US degree-granting educational institutions. In 1992 there were more than 370,000 hosts in this domain
- GOV
- US non-military government organisations.
- MIL
- US military organisations
- NET
- The domain for the Internet backbone systems. Only machines actually necessary for the operation of the network can be registered here
- ORG
- US Non profit making organisations
- US
- For US home and small corporation users
- INT
- Special domain for international organisations like NATO
The proper terminology for a site's domain is its Fully Qualified Domain Name
(FQDN). It is usually selected to give a clear indication of the site's
organisation or sponsoring agent so it is usually relatively easy to glean the
meaning of a domain-name.
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