This document discusses the Domain Name System.
There are no specific requirements for this document.
This document is not restricted to specific software and hardware
The Domain Name System (DNS) is the system in the Internet that maps
names of objects (usually host names) into IP numbers or other resource record
values. The name space of the Internet is divided into domains, and the
responsibility for managing names within each domain is delegated, typically to
systems within each domain.
For example, all Internet systems that belong to the University of
Arizona have names within the arizona.edu domain. The Internet's root name
servers delegate the responsibility for managing the arizona.edu name space to
a name server system operated by University of Arizona's CCIT Telecom (a system
which also happens to be called arizona.edu with the IP addresses
18.104.22.168 and 22.214.171.124).
The Telecom name server can, in turn, delegate portions of the
arizona.edu name space to departmental name servers on campus. By this system,
the department gains a measure of autonomy in inventing and managing the names
within its subdomain. For example, some or all of the subdomains of arizona.edu
can be nameserved by various departments (such as Computer Science, Math, or
In addition to the Internet being divided namewise into domains and
subdomains, such as arizona.edu for University of Arizona and apple.com for
Apple Computer, it is divided numberwise into networks and subnets, such as
126.96.36.199 or 188.8.131.52. for University of Arizona and Apple, respectively.
The namewise layout of the Internet tracks administrative responsibility
(ownership), while the numberwise layout tracks physical topology.
There is no necessary relationship between the name(s) of an object in
the Internet and its number(s). For example, the 184.108.40.206 network physically
resides at the University of Arizona. However, if a machine that belongs to
Apple were to be plugged into the University of Arizona network, its name would
still be something.apple.com, even though its number would be 128.196.xxx.yyy.
In this case, however, Apple and the University of Arizona would share
nameservice responsibility for this system: Apple for the name-to-number
nameservice, and University of Arizona for the number-to-name nameservice.
The primary job that DNS performs is to map between names and numbers.
Most importantly, it must provide the translation from host names to IP
addresses, so that applications can effect a network connection from a command
such as ftp prep.ai.mit.edu. Also, DNS must map from IP addresses back to names
in order to provide some level of authentication, as with the
Reverse mapping from IP addresses to host names is performed under the
auspices of the IN-ADDR.ARPA pseudo-domain. Because the order of significance
in the naming system is highest on the right, the notation for addresses is
reversed. Therefore, the DNS entry for the IP address 220.127.116.11 is given