The hierarchy of labels in a domain name.
This article is about domain names in the Internet. For other uses, see
Domain.
A
domain name is a unique name that identifies an internet resource such as a website. It is an identification
string that defines a realm of administrative autonomy, authority or control on the
Internet. Domain names are formed by the rules
Domain Name System (DNS). Any name registered in the DNS is a domain name. The functional description of
domain names is presented in the
Domain Name System article. Broader usage and industry aspects are captured here.
Domain names are used in various networking contexts and
application-specific naming and addressing purposes. In general, a
domain name represents an
Internet Protocol (IP) resource, such as a personal computer used to access the Internet, a server computer hosting a
web site,
or the web site itself or any other service communicated via the
Internet. In 2010, the number of active domains reached 196 million.
[1]
Domain names are organized in subordinate levels (subdomains) of the
DNS root domain, which is nameless. The first-level set of domain names are the
top-level domains (TLDs), including the
generic top-level domains (gTLDs), such as the prominent domains
com,
info,
net,
edu, and
org, and the
country code top-level domains
(ccTLDs). Below these top-level domains in the DNS hierarchy are the
second-level and third-level domain names that are typically open for
reservation by end-users who wish to connect local area networks to the
Internet, create other publicly accessible Internet resources or run web
sites. The registration of these domain names is usually administered
by
domain name registrars who sell their services to the public.
A
fully qualified domain name (FQDN) is a domain name that is completely specified in the hierarchy of the DNS, having no parts omitted.
Domain names are usually written in lowercase, although labels in the Domain Name System are
case-insensitive.
Purpose
Domain names serve as more easily memorable names for Internet
resources such as computers, networks, and services. A domain name
represents an Internet Protocol (IP) resource. Individual Internet host
computers use domain names as host identifiers, or host names. Host
names are the leaf labels in the domain name system usually without
further subordinate domain name space. Host names appear as a component
in
Uniform Resource Locators (URLs) for Internet resources such as
web sites (e.g., en.wikipedia.org).
Domain names are also used as simple identification labels to
indicate ownership or control of a resource. Such examples are the realm
identifiers used in the
Session Initiation Protocol (SIP), the
Domain Keys used to verify DNS domains in
e-mail systems, and in many other
Uniform Resource Identifiers (URIs).
An important function of domain names is to provide easily recognizable and memorizable names to numerically
addressed
Internet resources. This abstraction allows any resource to be moved to
a different physical location in the address topology of the network,
globally or locally in an
intranet.
Such a move usually requires changing the IP address of a resource and
the corresponding translation of this IP address to and from its domain
name.
Domain names are used to establish a unique identity. Organizations
can choose a domain name that corresponds to their name, helping
Internet users to reach them easily. For instance IBM's web site is at
ibm.com, and GNU's is at gnu.org.
Generic domain names increase popularity. A generic domain name may
sometimes define an entire category of business that a company is
involved in, rather than being the name of the company. Some examples of
generic names include books.com, music.com, travel.com and art.com.
Companies have created successful brands based on a generic name, and
such generic domain names tend to be very valuable.
Domain names are often referred to simply as
domains and domain name registrants are frequently referred to as
domain owners,
although domain name registration with a registrar does not confer any
legal ownership of the domain name, only an exclusive right of use for a
particular duration of time. The use of domain names in commerce may
subject them to
trademark law.
History
The practice of using a simple memorable abstraction of a host's numerical address on a computer network dates back to the
ARPANET
era, before the advent of today's commercial Internet. In the early
network, each computer on the network retrieved the hosts file (
host.txt) from a computer at SRI (now
SRI International).
[2][3]
which mapped computer host names to numerical addresses. The rapid
growth of the network made it impossible to maintain a centrally
organized hostname registry and in 1983 the Domain Name System was
introduced on the ARPANET and published by the
Internet Engineering Task Force as
RFC 882 and
RFC 883.
Domain name space
Today, the
Internet Corporation for Assigned Names and Numbers (ICANN) manages the top-level development and architecture of the Internet domain name space. It authorizes
domain name registrars, through which domain names may be registered and reassigned.
The hierarchical domain name system, organized into zones, each served by domain name servers.
The domain name space consists of a
tree of domain names. Each node in the tree holds information associated with the domain name. The tree sub-divides into
zones beginning at the
DNS root zone.
Domain name syntax
A domain name consists of one or more parts, technically called
labels, that are conventionally concatenated, and delimited by dots, such as
example.com.
- The right-most label conveys the top-level domain; for example, the domain name www.example.com belongs to the top-level domain com.
- The hierarchy of domains descends from the right to the left label
in the name; each label to the left specifies a subdivision, or subdomain of the domain to the right. For example: the label example specifies a node example.com as a subdomain of the com domain, and www is a label to create www.example.com, a subdomain of example.com. This tree of labels may consist of 127 levels. Each label may contain from 1 to 63 octets.
The empty label is reserved for the root node. The full domain name may
not exceed a total length of 253 ASCII characters in its textual
representation.[4] In practice, some domain registries may have shorter limits.
- A hostname is a domain name that has at least one associated IP address. For example, the domain names www.example.com and example.com are also hostnames, whereas the com
domain is not. However, other top-level domains, particularly country
code top-level domains, may indeed have an IP address, and if so, they
are also hostnames.
- Hostnames impose restrictions on the characters allowed in the
corresponding domain name. A valid hostname is also a valid domain name,
but a valid domain name may not necessarily be valid as a hostname.
Top-level domains
The
top-level domains (TLDs) such as com, net and org are the highest level of domain names of the Internet. Top-level domains form the
DNS root zone of the hierarchical
Domain Name System. Every domain name ends with a top-level domain label.
When the Domain Name System was devised, in the 1980s, the domain name space was divided into two main groups of domains.
[5] The
country code top-level domains (ccTLD) were primarily based on the two-character territory codes of
ISO-3166 country abbreviations. In addition, a group of seven
generic top-level domains (gTLD) was implemented which represented a set of categories of names and multi-organizations.
[6] These were the domains
gov,
edu,
com,
mil,
org,
net, and
int.
During the growth of the Internet, it became desirable to create
additional generic top-level domains. As of October 2009, 21 generic
top-level domains and 250 two-letter country-code top-level domains
existed.
[7] In addition, the
ARPA domain serves technical purposes in the infrastructure of the Domain Name System.
During the 32nd International Public ICANN Meeting in Paris in 2008,
[8] ICANN started a new process of TLD naming policy to take a "
significant step forward on the introduction of new generic top-level domains."
This program envisions the availability of many new or already proposed
domains, as well as a new application and implementation process.
[9] Observers believed that the new rules could result in hundreds of new top-level domains to be registered.
[10]
IANA maintains an
annotated list of top-level domains in the root zone database as well as a
list of special-use (reserved) top-level domain names.
Second-level and lower level domains
Below the top-level domains in the domain name hierarchy are the
second-level domain
(SLD) names. These are the names directly to the left of .com, .net,
and the other top-level domains. As an example, in the domain
example.co.uk,
co is the second-level domain.
Next are third-level domains, which are written immediately to the
left of a second-level domain. There can be fourth- and fifth-level
domains, and so on, with virtually no limitation. An example of an
operational domain name with four levels of domain labels is
sos.state.oh.us. Each label is separated by a
full stop (dot). 'sos' is said to be a sub-domain of 'state.oh.us', and 'state' a sub-domain of 'oh.us', etc. In general,
subdomains are domains subordinate to their parent domain. An example of very deep levels of subdomain ordering are the
IPv6 reverse resolution
DNS zones,
e.g.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa,
which is the reverse DNS resolution domain name for the IP address of a
loopback interface, or the
localhost name.
Second-level (or lower-level, depending on the established parent
hierarchy) domain names are often created based on the name of a company
(e.g.
bbc.co.uk), product or service (e.g.
hotmail.com). Below these levels, the next domain name component has been used to designate a particular host server. Therefore,
ftp.example.com might be an FTP server,
www.example.com would be a
World Wide Web server, and
mail.example.com
could be an email server, each intended to perform only the implied
function. Modern technology allows multiple physical servers with either
different (cf.
load balancing) or even identical addresses (cf.
anycast)
to serve a single hostname or domain name, or multiple domain names to
be served by a single computer. The latter is very popular in
Web hosting service centers, where service providers host the websites of many organizations on just a few servers.
The hierarchical
DNS labels or components of domain names are separated in a fully qualified name by the
full stop (dot,
.).
Internationalized domain names
The character set allowed in the Domain Name System is based on
ASCII and does not allow the representation of names and words of many languages in their native scripts or alphabets.
ICANN approved the
Internationalized domain name (IDNA) system, which maps
Unicode strings used in application user interfaces into the valid DNS character set by an encoding called
Punycode. For example, københavn.eu is mapped to xn--kbenhavn-54a.eu. Many
registries have adopted IDNA.
Domain name registration
History
The first commercial Internet domain name, in the TLD
com, was registered on 15 March 1985 in the name
symbolics.com by Symbolics Inc., a computer systems firm in Cambridge, Massachusetts.
By 1992, fewer than 15,000
com domains had been registered.
In December 2009, 192 million domain names had been registered.
[11] A large fraction of them are in the
com
TLD, which as of March 15, 2010 had 84 million domain names, including
11.9 million online business and e-commerce sites, 4.3 million
entertainment sites, 3.1 million finance related sites, and 1.8 million
sports sites.
[12] As of July 2012 the
com TLD has more registrations than all of the ccTLDs combined.
[13]
Administration
The right to use a domain name is delegated by
domain name registrars, which are accredited by the
Internet Corporation for Assigned Names and Numbers
(ICANN), the organization charged with overseeing the name and number
systems of the Internet. In addition to ICANN, each top-level domain
(TLD) is maintained and serviced technically by an administrative
organization operating a registry. A registry is responsible for
maintaining the database of names registered within the TLD it
administers. The registry receives registration information from each
domain name registrar authorized to assign names in the corresponding
TLD and publishes the information using a special service, the
WHOIS protocol.
Registries and registrars usually charge an annual fee for the
service of delegating a domain name to a user and providing a default
set of name servers. Often, this transaction is termed a sale or lease
of the domain name, and the registrant may sometimes be called an
"owner", but no such legal relationship is actually associated with the
transaction, only the exclusive right to use the domain name. More
correctly, authorized users are known as "registrants" or as "domain
holders".
ICANN
publishes the complete list of TLD registries and domain name
registrars. Registrant information associated with domain names is
maintained in an online database accessible with the WHOIS protocol. For
most of the 250
country code top-level domains (ccTLDs), the domain registries maintain the WHOIS (Registrant, name servers, expiration dates, etc.) information.
Some domain name registries, often called
network information centers (NIC), also function as registrars to end-users. The major generic top-level domain registries, such as for the
COM,
NET,
ORG,
INFO domains and others, use a registry-registrar model consisting of hundreds of domain name registrars (see lists at
ICANN or
VeriSign).
In this method of management, the registry only manages the domain name
database and the relationship with the registrars. The
registrants (users of a domain name) are customers of the registrar, in some cases through additional layers of resellers.
Technical requirements and process
In the process of registering a domain name and maintaining authority
over the new name space created, registrars use several key pieces of
information connected with a domain:
- Administrative contact. A registrant usually designates an
administrative contact to manage the domain name. The administrative
contact usually has the highest level of control over a domain.
Management functions delegated to the administrative contacts may
include management of all business information, such as name of record,
postal address, and contact information of the official registrant of
the domain and the obligation to conform to the requirements of the
domain registry in order to retain the right to use a domain name.
Furthermore the administrative contact installs additional contact
information for technical and billing functions.
- Technical contact. The technical contact manages the name
servers of a domain name. The functions of a technical contact include
assuring conformance of the configurations of the domain name with the
requirements of the domain registry, maintaining the domain zone
records, and providing continuous functionality of the name servers
(that leads to the accessibility of the domain name).
- Billing contact. The party responsible for receiving billing invoices from the domain name registrar and paying applicable fees.
- Name servers. Most registrars provide two or more name
servers as part of the registration service. However, a registrant may
specify its own authoritative name servers
to host a domain's resource records. The registrar's policies govern
the number of servers and the type of server information required. Some
providers require a hostname and the corresponding IP address or just
the hostname, which must be resolvable either in the new domain, or
exist elsewhere. Based on traditional requirements (RFC 1034), typically a minimum of two servers is required.
Domain names may be formed from the set of alphanumeric ASCII
characters (a-z, A-Z, 0-9), but characters are case-insensitive. In
addition the hyphen is permitted if it is surrounded by a characters or
digits, i.e., it is not the start or end of a label. Labels are always
separated by the
full stop (period) character in the textual name representation.
Business models
Domain names are often seen in analogy to
real estate
in that (1) domain names are foundations on which a website (like a
house or commercial building) can be built and (2) the highest "quality"
domain names, like sought-after real estate, tend to carry significant
value, usually due to their online brand-building potential, use in
advertising,
search engine optimization, and many other criteria.
A few companies have offered low-cost, below-cost or even cost-free
domain registrations with a variety of models adopted to recoup the
costs to the provider. These usually require that domains be hosted on
their website within a framework or portal that includes advertising
wrapped around the domain holder's content, revenue from which allows
the provider to recoup the costs. Domain registrations were free of
charge when the DNS was new. A domain holder can give away or sell
infinite number of
subdomains under their domain name. For example, the owner of
example.org could provide subdomains such as
foo.example.org and
foo.bar.example.org to interested parties.
Because of the popularity
of the Internet, many desirable domain names are already assigned and
users must search for other acceptable names, using Web-based search
features, or
WHOIS and
dig operating system tools. Many registrars have implemented
Domain name suggestion
tools which search domain name databases and suggest available
alternative domain names related to keywords provided by the user.
Resale of domain names
The business of resale of registered domain names is known as the
domain aftermarket. Various factors influence the perceived value or market value of a domain name.
Most of the million dollar domain deals are carried out privately and
go unreported. As of 2011, the most expensive domain name sales on
record were:
- Insure.com $16 million in 2009 [14]
- Fund.com 2008 £9.99 million[14]
- Sex.com for $14 million in October 2010[14][15]
- Porn.com 2007 $9.5 million[14]
- Fb.com for $8.5 million in November 2010[14][not in citation given]
Domain name confusion
Intercapping
is often used to emphasize the meaning of a domain name. However, DNS
names are not case-sensitive, and some names may be misinterpreted in
certain uses of capitalization. For example:
Who Represents, a database of artists and agents, chose
whorepresents.com, which can be misread as
whore presents. Similarly, a therapists' network is named
therapistfinder.com. In such situations, the proper meaning may be clarified by use of hyphens in the domain name. For instance,
Experts Exchange, a programmers' discussion site, for a long time used
expertsexchange.com, but ultimately changed the name to
experts-exchange.com.
Intellectual property entrepreneur
Leo Stoller threatened to sue the owners of StealThisEmail.com on the basis that, when read as
stealthisemail.com, it infringed on claimed (but invalid) trademark rights to the word "stealth".
Use in web site hosting
The domain name is a component of a
Uniform Resource Locator (URL) used to access
web sites, for example:
- URL: http://www.example.net/index.html
- Top-level domain name: net
- Second-level domain name: example.net
- Host name: www.example.net
A domain name may point to multiple
IP addresses
in order to provide server redundancy for the cybernetic services to be
delivered; such multi-address capability is used to manage the traffic
of large, popular web sites. More commonly, however, one
server computer, at a given IP address, may also host web sites in different domains. Such address overloading enables
virtual web hosting, commonly used by large
web hosting services
to conserve IP address space. IP-address overloading is possible
through a feature in the HTTP version 1.1 protocol, but not in the HTTP
version 1.0 protocol, which requires that a request identify the domain
name being referred for connection.
Abuse and regulation
Critics often claim abuse of administrative power over domain names. Particularly noteworthy was the
VeriSign Site Finder
system which redirected all unregistered .com and .net domains to a
VeriSign webpage. For example, at a public meeting with VeriSign to air
technical concerns about SiteFinder,
[16] numerous people, active in the
IETF
and other technical bodies, explained how they were surprised by
VeriSign's changing the fundamental behavior of a major component of
Internet infrastructure, not having obtained the customary consensus.
SiteFinder, at first, assumed every Internet query was for a website,
and it monetized queries for incorrect domain names, taking the user to
VeriSign's search site. Unfortunately, other applications, such as many
implementations of email, treat a lack of response to a domain name
query as an indication that the domain does not exist, and that the
message can be treated as undeliverable. The original VeriSign
implementation broke this assumption for mail, because it would always
resolve an erroneous domain name to that of SiteFinder. While VeriSign
later changed SiteFinder's behaviour with regard to email, there was
still widespread protest about VeriSign's action being more in its
financial interest than in the interest of the Internet infrastructure
component for which VeriSign was the steward.
Despite widespread criticism, VeriSign only reluctantly removed it after the
Internet Corporation for Assigned Names and Numbers
(ICANN) threatened to revoke its contract to administer the root name
servers. ICANN published the extensive set of letters exchanged,
committee reports, and ICANN decisions.
[17]
There is also significant disquiet regarding the United States'
political influence over ICANN. This was a significant issue in the
attempt to create a
.xxx top-level domain and sparked greater interest in
alternative DNS roots that would be beyond the control of any single country.
[18]
Additionally, there are numerous accusations of
domain name front running,
whereby registrars, when given whois queries, automatically register
the domain name for themselves. Network Solutions has been accused of
this.
[19]
Truth in Domain Names Act
In the United States, the
Truth in Domain Names Act of 2003, in combination with the
PROTECT Act of 2003, forbids the use of a misleading domain name with the intention of attracting Internet users into visiting
Internet pornography sites.
The Truth in Domain Names Act follows the more general
Anticybersquatting Consumer Protection Act passed in 1999 aimed at preventing
typosquatting and deceptive use of names and trademarks in domain names.
Seizures
In the early 21st century, the US Department of Justice (DOJ) began using a tactic of
seizing
domain names, based on the legal theory that domain names constitute
property used to engage in criminal activity, and thus are subject to
forfeiture. For example, in the seizure of the domain name of a gambling website, the DOJ referenced
18 U.S.C. § 981 and
18 U.S.C. § 1955(d).
[20][dead link]. In 2013 the US government seized
Liberty Reserve, citing
18 U.S.C. § 982(a)(1).
[21]
The U.S. Congress passed the
Combating Online Infringement and Counterfeits Act in 2010. Consumer Electronics Association vice president Petricone was worried that seizure was a
blunt instrument that could harm legitimate businesses.
[22][23]
After a joint operation in February 15, 2011, the DOJ and the
Department of Homeland Security claimed to have seized ten domains of
websites involved in advertising and distributing child pornography, but
also mistakenly seized the domain name of a large DNS provider,
temporarily replacing 84,000 websites with seizure notices.
[24]
Fictitious domain name
A
fictitious domain name is a domain name used in a work of
fiction or popular culture to refer to a domain that does not actually
exist, often with invalid or unofficial
top-level domains such as "
.web", a usage exactly analogous to the dummy
555 telephone number prefix used in film and other media. The canonical fictitious domain name is "
example.com", specifically set aside by IANA in
RFC 2606 for such use, along with the
.example TLD.
Domain names used in works of fiction have often been registered in the DNS, either by their creators or by
cybersquatters attempting to profit from it. This phenomenon prompted
NBC to purchase the domain name
Hornymanatee.com after talk-show host
Conan O'Brien spoke the name while ad-libbing on
his show. O'Brien subsequently created a website based on the concept and used it as a
running gag on the show.
[25]
See also
References
- "Verisign 8-k Current Report".
- RFC 3467, Role of the Domain Name System (DNS), J.C. Klensin, J. Klensin (February 2003)
- Cricket Liu, Paul Albitz (2006). DNS and BIND (5th ed.). O'Reilly. p. 3.
- RFC 1035, Domain names--Implementation and specification, P. Mockapetris (Nov 1987)
- "Introduction to Top-Level Domains (gTLDs)". Internet Corporation for Assigned Names and Numbers.
- RFC 920, Domain Requirements, J. Postel, J. Reynolds, The Internet Society (October 1984)
- "New gTLD Program", ICANN, October 2009
- "32nd International Public ICANN Meeting". ICANN. 2008-06-22.
- "New gTLS Program". ICANN. Retrieved 2009-06-15.
- ICANN Board Approves Sweeping Overhaul of Top-level Domains, CircleID, 26 June 2008.
- Internet Tops 192 Million Domain Name Registrations, Feb 22, 2010.
- Evangelista, Benny. 2010. "25 years of .com names." San Francisco Chronicle. March 15, p. 1
- "Domain domination: The com TLD larger than all ccTLDs combined". Royal.pingdom.com. Retrieved 2012-07-25.
- Irvine, Chris (10 Mar 2010). "Top 10 most expensive domain names". The Telegraph. Retrieved 23 November 2011.
- Merritt, Tom (May 29, 2009). "Top 5 most expensive domain names". CNET TV. Retrieved 23 November 2011.
- McCullagh, Declan (2003-10-03). "VeriSign fends off critics at ICANN confab". CNET News.com. Retrieved 2007-09-22.
- Internet Corporation for Assigned Names and Numbers (ICANN). "Verisign's Wildcard Service Deployment". Retrieved 2007-09-22.
- Mueller, M (March 2004). Ruling the Root. MIT Press. ISBN 0-262-63298-5.
- Slashdot.org, NSI Registers Every Domain Checked
- FBI / DOJ (15 April 2011). "Warning". Retrieved 2011-04-15.
- libertyreserve dot com, accessed 5/29/2013
- Declan McCullagh (18 November 2010). "Senate panel approves domain name seizure bill". CNET. Retrieved 2011-04-15.
- Sarah Jerome (6 April 2011). "Tech industry wary of domain name seizures". thehill.com. Retrieved 2011-04-15.
- "U.S. Government Shuts Down 84,000 Websites, ‘By Mistake’".
- "So This Manatee Walks Into the Internet", New York Times, December 12, 2006. Accessed April 12, 2008.
External links
Some
of the most mysterious features of the Internet are domain names and
URLs. Many people recognize that you have to know a website’s “address”
in order to connect with the site, but where these addresses come from
and how to obtain one is a lot less understood. Unfortunately, the term
“domain” is not simple to understand. If you look in Wikipedia, there
are dozens of different uses and meanings for the term in mathematics,
science, general use and information technology. See Wikipedia:Domain. However, in the context of the Internet, the term “domain name”
has a more specific meaning. A domain name is a string of letters that
defines a section of the Internet, more specifically a realm of
administrative autonomy, authority or control. See Wikipedia:Domain name. In common use, a domain name can be thought of as the address of a website.
