Network Working Group P. Mockapetris
Request for Comments: 1034 ISI
Obsoletes: RFCs 882, 883, 973 November 1987
DOMAIN NAMES - CONCEPTS AND FACILITIES
1. STATUS OF THIS MEMO
This RFC is an introduction to the Domain Name System (DNS), and omits
many details which can be found in a companion RFC, "Domain Names -
Implementation and Specification" [RFC-1035]. That RFC assumes that the
reader is familiar with the concepts discussed in this memo.
A subset of DNS functions and data types constitute an official
protocol. The official protocol includes standard queries and their
responses and most of the Internet class data formats (e.g., host
However, the domain system is intentionally extensible. Researchers are
continuously proposing, implementing and experimenting with new data
types, query types, classes, functions, etc. Thus while the components
of the official protocol are expected to stay essentially unchanged and
operate as a production service, experimental behavior should always be
expected in extensions beyond the official protocol. Experimental or
obsolete features are clearly marked in these RFCs, and such information
should be used with caution.
The reader is especially cautioned not to depend on the values which
appear in examples to be current or complete, since their purpose is
primarily pedagogical. Distribution of this memo is unlimited.
This RFC introduces domain style names, their use for Internet mail and
host address support, and the protocols and servers used to implement
domain name facilities.
2.1. The history of domain names
The impetus for the development of the domain system was growth in the
- Host name to address mappings were maintained by the Network
Information Center (NIC) in a single file (HOSTS.TXT) which
was FTPed by all hosts [RFC-952, RFC-953]. The total network
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bandwidth consumed in distributing a new version by this
scheme is proportional to the square of the number of hosts in
the network, and even when multiple levels of FTP are used,
the outgoing FTP load on the NIC host is considerable.
Explosive growth in the number of hosts didn't bode well for
- The network population was also changing in character. The
timeshared hosts that made up the original ARPANET were being
replaced with local networks of workstations. Local
organizations were administering their own names and
addresses, but had to wait for the NIC to change HOSTS.TXT to
make changes visible to the Internet at large. Organizations
also wanted some local structure on the name space.
- The applications on the Internet were getting more
sophisticated and creating a need for general purpose name
The result was several ideas about name spaces and their management
[IEN-116, RFC-799, RFC-819, RFC-830]. The proposals varied, but a
common thread was the idea of a hierarchical name space, with the
hierarchy roughly corresponding to organizational structure, and names
using "." as the character to mark the boundary between hierarchy
levels. A design using a distributed database and generalized resources
was described in [RFC-882, RFC-883]. Based on experience with several
implementations, the system evolved into the scheme described in this
The terms "domain" or "domain name" are used in many contexts beyond the
DNS described here. Very often, the term domain name is used to refer
to a name with structure indicated by dots, but no relation to the DNS.
This is particularly true in mail addressing [Quarterman 86].
2.2. DNS design goals
The design goals of the DNS influence its structure. They are:
- The primary goal is a consistent name space which will be used
for referring to resources. In order to avoid the problems
caused by ad hoc encodings, names should not be required to
contain network identifiers, addresses, routes, or similar
information as part of the name.
- The sheer size of the database and frequency of updates
suggest that it must be maintained in a distributed manner,
with local caching to improve performance. Approaches that
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attempt to collect a consistent copy of the entire database
will become more and more expensive and difficult, and hence