In the Domain Name System hierarchy, a second-level domain is a domain that is directly below a top-level domain. For example, in example.com, example is the second-level domain of the .com TLD. Second-level domains commonly refer to the organization that registered the domain name with a domain name registrar. Some domain name registries 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 namespace a college or other academic institution would register under the .ac.ukccSLD, while companies would register under .co.uk. Some TLDs now break the traditional rule that a TLD is the right most node in a URL. A TLD can have multiple nodes, like pvt.k12.ma.us. 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.
Country-code second-level domains
Australia
Austria
In Austria there are two second-level domains available for the public:
.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 by . There 17 active second-level domains under the.tr 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.
There are several second-level domains which are no longer available.
Australia
Second-level domains under.au which are no longer available include: .conf.au originally intended for conferences; .gw.au for the Australian Academic and Research networks; info.au for general information, .otc.au and .telememo.au 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 while others have remained under the provincial two letter SLD while others have been moved to more traditional subdomains.
France
Historic second-level domains for France included: .tm.fr,.com.fr and .asso.fr.
Historic second-level domains for The Netherlands included: .co.nl
Yugoslavia
In 2006 the.yu ccTLD was replaced by rs and.me. Second-level domains under.yu included: .ac.yu – for academic institutions, .co.yu for commercial enterprises; .org.yu for organizations and .cg.yu for residents of Montenegro. Only legal entities were allowed to register names under.yu and its second-level domains.
Tuvalu
Historic second-level domains for Tuvalu included:
Legal issues
As a result of ICANN's generic top-level domain expansion, the risk of domain squatting has increased significantly. For example, based on current regulations, the registration of the gTLDs.olympics or.redcross is not allowed, however the registration of sites such as olympics.example or redcross.example is not controlled. Experts say that further restrictions are needed for second-level domains under the new gTLD.health, as well. For example, second-level domains under .tobacco.health or .diet.health can be easily misused by companies and therefore are a potential threat to Internet users.
