In the
Domain Name System
The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned to ...
(DNS) hierarchy, a second-level domain (SLD or 2LD) is a domain that is directly below a
top-level domain
A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain. The top-level domain names are installed in the root zone of the name space. For all domains in ...
(TLD). For example, in , is the second-level domain of the TLD.
Second-level domains commonly refer to the organization that registered the domain name with a
domain name registrar
A domain name registrar is a company that manages the reservation of Internet domain names. A domain name registrar must be accredited by a generic top-level domain (gTLD) registry or a country code top-level domain (ccTLD) registry. A registrar ...
. Some
domain name registries
Domain may refer to:
Mathematics
*Domain of a function, the set of input values for which the (total) function is defined
**Domain of definition of a partial function
**Natural domain of a partial function
**Domain of holomorphy of a function
*Dom ...
introduce a second-level hierarchy to a TLD that indicates the type of entity intended to register an SLD under it. For example, in the
.uk
.uk is the Internet country code top-level domain (ccTLD) for the United Kingdom. It was first registered in July 1985, seven months after the original generic top-level domains such as .com and the first country code after .us.
, it is the fift ...
namespace a college or other academic institution would register under the
ccSLD
A country code second-level domain is a second-level domain to a country code top-level domain. Such a domain may be reserved by a domain name registry for the registration of third-level domains, or assigned to a third party as a subdomain.
Many ...
, while companies would register under . Strictly speaking, domains like
.ac.uk and
.co.uk are second level domain themselves, since they are right below a TLD. A list of the official TLDs can be found at icann.org and iana.org. An ordinal-free term to denote domains under which people can register their own domain name is public suffix domain (PSD).
Country-code second-level domains
Algeria
Australia
Austria
In Austria there are two second-level domains available for the public:
*.co.at intended for commercial enterprises
*.or.at intended for organizations.
The second-level domain
*.priv.at is restricted to Austrian citizens only, while
*.ac.at and .gv.at are reserved for educational institutions and governmental bodies respectively.
Brazil
France
In France, there are various second-level domains available for certain sectors, including
*.avocat.fr for attorneys,
*.aeroport.fr for airports and
*.veterinaire.fr for vets.
Hungary
New Zealand
Pakistan
India
Israel
Japan
Russia
South Africa
South Korea
Spain
Sri Lanka
Thailand
Trinidad and Tobago
* co.tt
* com.tt
* org.tt
* net.tt
* travel.tt
* museum.tt
* aero.tt
* tel.tt
* name.tt
* charity.tt
* mil.tt
* edu.tt
* gov.tt
Turkey
In Turkey, domain registrations, including the registration of second-level domains is administrated b
nic.tr
There 17 active second-level domains under the
.tr
.tr is the Internet country code top-level domain (ccTLD) for Turkey. It is administered by trABİS (under the Information and Communication Technologies Authority of Turkey) and managed by the Computer Center DNS Group of the ICT Authority. The ...
TLD. The registration of domains is restricted to Turkish individuals and businesses, or foreign companies with a business activity in Turkey.
Second-level domains include ''.com.tr'' for commercial ventures, ''.edu.tr'' for academic institutions and ''.name.tr'' for personal use.
Ukraine
Ukraine second-level domains include:
*.gov.ua – available for government agencies.
*.com.ua – for commercial use.
*.in.ua – for commercial use.
*.org.ua – intended for non-profit organizations.
*.net.ua – intended for Internet providers.
*.edu.ua – for academic institutions.
There are also numerous geographic names.
United Kingdom
United States
A two-letter second-level domain is formally reserved for each U.S. state, federal territory, and the District of Columbia.
Zambia
Historic second-level domains
There are several second-level domains which are no longer available.
Australia
Second-level domains under .au which are no longer available include: originally intended for conferences; for the Australian Academic and Research networks; ' for general information, ' and ' for the X.400 mail systems.
Canada
Prior to 12 Oct 2010 there were second level domain based on province:
.ab.ca — Alberta, .bc.ca — British Columbia, .mb.ca — Manitoba, .nb.ca — New Brunswick, .nf.ca — Newfoundland, .nl.ca — Newfoundland and Labrador, .ns.ca — Nova Scotia, .nt.ca — Northwest Territories, .nu.ca — Nunavut, .on.ca — Ontario, .pe.ca — Prince Edward Island, .qc.ca — Quebec, .sk.ca — Saskatchewan, .yk.ca — Yukon
Since 2010, some have been replaced (for example, alberta.ca) while others have remained under the provincial two letter SLD (e.g., Calgary Board of Education www.cbe.ab.ca) and others were moved to more traditional subdomains (www.transportation.alberta.ca).
France
Historic second-level domains for France included:
''.tm.fr'' (for brands), .''com.fr'' (for commercial use) and ''{{Not a typo, .asso.fr.''
The Netherlands
Historic second-level domains for the Netherlands included:
.''co.nl'' (for commercial use)
Yugoslavia
In 2006 the {{Not a typo, .yu ccTLD was replaced by ''{{Not a typo, .rs'' (for Serbia) and ''{{Not a typo, .me'' (for Montenegro).
Second-level domains under {{Not a typo, .yu included:
''{{Not a typo, .ac.yu'' – for academic institutions, ''{{Not a typo, .co.yu'' for commercial enterprises; ''{{Not a typo, .org.yu'' for organizations and ''{{Not a typo, .cg.yu'' for residents of Montenegro.
Only legal entities were allowed to register names under ''{{Not a typo, .yu'' and its second-level domains.
Tuvalu
Historic second-level domains for Tuvalu included
co.tv
Legal issues
As a result of ICANN's generic top-level domain (gTLD) expansion, the risk of
domain squatting has increased significantly. For example, based on current regulations, the registration of the gTLDs ''{{Not a typo, .olympics'' or ''{{Not a typo, .redcross'' is not allowed; however, the registration of sites such as ''{{Not a typo, olympics.example'' or ''{{Not a typo, redcross.example'' is not controlled.
Experts say {{who, date=May 2021 that further restrictions are needed for second-level domains under the new gTLD ''{{Not a typo, .health'', as well. For example, second-level domains under ''{{Not a typo, .tobacco.health'' or ''{{Not a typo, .diet.health'' can be easily misused by companies and therefore are a potential threat to Internet users.
[{{cite journal, last1=Mackey, first1=TK, last2=Liang, first2=BA, last3=Kohler, first3=JC, last4=Attaran, first4=A, title=Health Domains for Sale: The Need for Global Health Internet Governance, journal=J Med Internet Res, date=5 March 2014, volume=16, issue=3, doi=10.2196/jmir.3276, pmid=24598602, url=http://www.jmir.org/2014/3/e62/, access-date=2014-10-29, pmc=3961808, page=e62]
See also
*
Single-letter second-level domains Single-letter second-level domains are domains in which the second-level domain of the domain name consists of only one letter, such as x.com. In 1993, the Internet Assigned Numbers Authority (IANA) explicitly reserved all single-letter and single-d ...
*
Domain Name System
The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned to ...
*
Top-level domain
A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain. The top-level domain names are installed in the root zone of the name space. For all domains in ...
*
Country code top-level domain
A country code top-level domain (ccTLD) is an Internet top-level domain generally used or reserved for a country, sovereign state, or dependent territory identified with a country code. All ASCII ccTLD identifiers are two letters long, and all t ...
*
Subdomain
In the Domain Name System (DNS) hierarchy, a subdomain is a domain that is a part of another (main) domain. For example, if a domain offered an online store as part of their website example.com, it might use the subdomain shop.example.com .
Ov ...
*
Private sub-domain registry
A private sub-domain registry allocates domain names in a subset of the Domain Name System under a domain registered with an ICANN-accredited or ccTLD registry. Most of the private sub-domain registries operate based on an ISO 3166-1 name that is ...
*
Public Suffix List The Public Suffix List (PSL) is a catalog of certain Internet domain names. Entries on the list are also referred to as effective top-level domains (eTLD).
The Mozilla Foundation initiated the suffix list for the security and privacy policies of its ...
*
.ac (second-level domain)
The sequence .ac (short for ''academia'') is in use in many countries as a second-level domain for academic institutions such as universities, colleges, and research institutes. In the United Kingdom and Japan, for example, academic institutions ...
*
.edu (second-level domain)
The sequence .edu (short for educational) is in use in many countries as a second-level domain for academic institutions such as universities, colleges, and research institutes.
Many countries use .ac for the same purpose. Still others do not m ...
References
{{Reflist
{{course assignment , course = Education Program:University College London/MSIN1003 Information World (Autumn 2014) , term = 2014 Q3
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Domain Name System