In the Domain Name System (DNS) hierarchy, a second-level domain (SLD or 2LD) is a domain that is directly below a top-level domain (TLD). 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.uk ccSLD, while companies would register under .co.uk.
Country-code second-level domains
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In Argentina, there are various second-level domains available for certain sectors, including
- com.ar - Companies and individuals resident in Argentina
- edu.ar - Educational institutions
- gob.ar, gov.ar - Local and national government
- int.ar - International entities and representatives of foreign international organisations in Argentina
- mil.ar - Military
- net.ar - Providers of internet services licensed by ENACOM (Ente Nacional de Comunicaciones, previously known as ComisiÃ³n Nacional de Comunicaciones)
- org.ar - For Non-profit organizations
- tur.ar - Tourism and travel companies licensed by the Ministerio de Turismo de la NaciÃ³n
- musica.ar - Any member of listed in the National Registry of Musicians and National Musical Groups
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.
There are at least 66 second level domains:
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.
.nz â" first level NZ domain, general use.
Open second-level domains (available for the public):
- .ac.nz â" for tertiary educational institutions and related organisations.
- .co.nz â" for commercial use.
- .school.nz â" Primary, secondary and pre-schools and related organisations
Closed second-level domains (restricted to certain sectors):
- .cri.nz â" for academic institutions.
- .govt.nz â" for government bodies.
- .mil.nz â" for the military organisation of the NZ Government.
- .parliament.nz â" for parliamentary agencies, offices, political parties, and their elected members.
There are eight Second Level Domains:
- org.il: Non-commercial Organizations; administration delegated to five private registrars.
- k12.il: Schools and Kindergartens
- gov.il: Government and Governmental System; administration delegated to ministry of finance.
- muni.il: Municipal Government
- idf.il: Israel Defense Forces; administration delegated to the army's Center of Computing and Information Systems.
Registration of other second-level domain names directly under .il is not supported.
Hebrew third level domains such as ×"××× ××¨× ×.org.il are available since 2010.
Second-level domain registrations are handled jointly by the official registry service CCTLDRU and private companies. There are currently 133 active second-level domains available for registration. This large number is because every geographical region has its own second-level domain, such as .volgograd.ru for the Volgograd Region, .irkutsk.ru for the Irkutsk region or msk.ru for Moscow. There also secondâ"level domains for specific sectors, such as ac.ru for academic institutions, com.ru for commercial enterprises or int.ru for international organizations.
Under the .za ccTLD there are several second-level domains in use. These include:
- .ac.za for academic institutions.
- .gov.za for government departments.
- .law.za for law firms and attorneys.
- .mil.za for the Department of Defence
- .nom.za for personal use. The registration is handled by NOM.ZA. and is available for free.
- .school.za for primary and secondary schools.
- .net.za for network providers.
Spanish second-level domains include .nom.es intended for personal names, .org.es for non-profit organizations and .gob.es for government agencies, com.es for commercial companies.
Thai second-level domains include:
- .ac.th or *.à¸¨à¸¶à¸à¸©à¸².à¹à¸à¸¢ for academic institutions
- .co.th or *.à¸à¸¸à¸£à¸à¸´à¸.à¹à¸à¸¢ for private business enterprises, state enterprises or Trademark
- .go.th or *.à¸£à¸±à¸à¸à¸²à¸¥.à¹à¸à¸¢ for a government and projects which are under government supervision
- .mi.th or *.à¸à¸«à¸²à¸£.à¹à¸à¸¢ military units
- .net.th or *.à¹à¸à¹à¸.à¹à¸à¸¢ licensed operators in telecommunication business
- .or.th or *.à¸à¸à¸à¹à¸à¸£.à¹à¸à¸¢ non government organizations or social projects
- .in.th or *.à¹à¸à¸¢ for a general public (natural persons and juristic persons)
Policy of .th and .à¹à¸à¸¢ service, Revised B.E.2561 (2018)
In Turkey, domain registrations, including the registration of second-level domains is administrated by nic.tr. 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.
Ukraine second-level domains include:
- .gov.ua â" available for government agencies.
- .com.ua â" for commercial use.
- .in.ua â" for commercial use.
- .org.ua â" intended for non-profit organizations.
- .net.ua â" available only for Internet providers in the UA.
- .edu.ua â" for academic institutions.
... and geographic names: cherkassy.ua, cherkasy.ua, chernigov.ua, chernihiv.ua, chernivtsi.ua, chernovtsy.ua, ck.ua, cn.ua, cr.ua, crimea.ua, cv.ua, dn.ua, dnepropetrovsk.ua, dnipropetrovsk.ua, dominic.ua, donetsk.ua, dp.ua, if.ua, ivano-frankivsk.ua, kh.ua, kharkiv.ua, kharkov.ua, kherson.ua, khmelnitskiy.ua, khmelnytskyi.ua, kiev.ua, kirovograd.ua, km.ua, kr.ua, krym.ua, ks.ua, kv.ua, kyiv.ua, lg.ua, lt.ua, lugansk.ua, lutsk.ua, lv.ua, lviv.ua, mk.ua, mykolaiv.ua, nikolaev.ua, od.ua, odesa.ua, odessa.ua, pl.ua, poltava.ua, rivne.ua, rovno.ua, rv.ua, sb.ua, sebastopol.ua, sevastopol.ua, sm.ua, sumy.ua, te.ua, ternopil.ua, uz.ua, uzhgorod.ua, vinnica.ua, vinnytsia.ua, vn.ua, volyn.ua, yalta.ua, zaporizhzhe.ua, zaporizhzhia.ua, zhitomir.ua, zhytomyr.ua, zp.ua, zt.ua
Currently there are 12 active second-level domains under the .uk top-level domain. The majority of the domains is administrated by the UK's domain registry services provider Nominet UK, while the others are managed by the British government. Generally, the registration of uk second-level domains is open to the public, however depending on the second-level domain there might by restrictions â" for example .me.uk is open to the public, but .ac.uk is only available to educational institutions.
- .co.uk â" intended for UK-based businesses. It is the UK's most widely used second-level domain.
- .org.uk â" intended for non-profit organizations.
- .me.uk â" available only for personal use.
- .ltd.uk â" available only for private limited companies in the UK.
- .plc.uk â" available only for public limited companies in the UK.
- .net.uk â" available only for Internet providers in the UK.
- .sch.uk â" available only for schools in the UK.
- .ac.uk â" intended for British academic institutions.
- .gov.uk â" available for government agencies.
- .mod.uk and .mil.uk â" available for the UK Armed Forces and Ministry of Defence.
- .nhs.uk â" registration restricted to the National Health Service only.
- .police.uk â" reserved for the UK police forces.
A two-letter second-level domain is formally reserved for each U.S. state, federal territory, and the District of Columbia:
Historic second-level domains
There are several second-level domains which are no longer available.
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.
Prior to 12 Oct 2010 there were second level domain based on province: .ab.ca â" Alberta, .bc.ca â" British Columbia, .mb.ca â" Manitoba, .nb.ca â" New Brunswick, .nf.ca â" Newfoundland, .nl.ca â" Newfoundland and Labrador, .ns.ca â" Nova Scotia, .nt.ca â" Northwest Territories, .nu.ca â" Nunavut, .on.ca â" Ontario, .pe.ca â" Prince Edward Island, .qc.ca â" Quebec, .sk.ca â" Saskatchewan, .yk.ca â" Yukon
Since 2010, some have been replaced (for example, alberta.ca) while others have remained under the provincial two letter SLD (e.g., transport Ontario www.mto.gov.on.ca) while others have been moved to more traditional subdomains (www.transportation.alberta.ca).
Historic second-level domains for France included: .tm.fr (for brands), .com.fr (for commercial use) and .asso.fr.
Historic second-level domains for The Netherlands included: .co.nl (for commercial use)
In 2006 the .yu ccTLD was replaced by rs (for Serbia) and .me (for Montenegro). Second-level domains under .yu included: .ac.yu â" 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.
Historic second-level domains for Tuvalu included: co.tv
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 .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.
- Single-letter second-level domains
- Domain Name System
- Top-level domain
- Country code top-level domain
- Private sub-domain registry
- Public Suffix List