Science Fair Project Encyclopedia
Country code top-level domain
A country code top-level domain (ccTLD) is a top-level domain used and reserved for a country or a dependent territory. These are two letters long, and most of them correspond to the ISO 3166-1 standard for country codes.
There are over 243 ccTLDs; see the list of Internet TLDs and IANA's list of ccTLDs. Most ccTLDs correspond to the two-letter ISO 3166-1 country codes, but there are several differences, explained below.
Each country appoints managers for its ccTLD and sets the rules for allocating domains. Some countries allow anyone in the world to acquire a domain in their ccTLD, for example Armenia (am), Austria (at) Cocos (Keeling) Islands (cc), Germany (de), Niue (nu), Samoa (ws), Tonga (to), Turkmenistan (tm) and Tuvalu (tv). This has resulted in the domain names I.am, start.at and go.to.
ISO 3166-1 codes not used as ccTLDs
The codes EH and KP, although theoretically available as ccTLDs for Western Sahara and North Korea, have never been assigned and do not exist in DNS. Similarly, the new codes CS (Serbia and Montenegro) and AX (Åland Islands) are not yet assigned as ccTLDs (cs was previously assigned to Czechoslovakia). TL (post-independence East Timor), is now being introduced to replace TP.
All other current ISO 3166-1 codes have been assigned and do exist in DNS. However, some of these are effectively unused. In particular, the ccTLDs for the Norwegian territories Bouvet Island (bv) and Svalbard (sj) do exist in DNS, but no subdomains have been assigned, and it is Norid policy not to assign any at present.
Only one domain (dra.hmg.gb, for the Defence Evaluation and Research Agency) is still registered in gb (United Kingdom, although the letters actually stand for Great Britain, a subset of the UK) and no new registrations are being accepted for it. Sites in the UK use uk (see below).
ccTLDs not in ISO 3166-1
Eight ccTLDs currently remain in use despite not being ISO 3166-1 two-letter codes:
- ac (Ascension Island), gg (Guernsey), im (Isle of Man) and je (Jersey): these codes came from IANA's decision in 1996 to allow the use of codes reserved in the ISO 3166-1 alpha-2 reserve list for use by the Universal Postal Union. The decision was later reversed, and only these four ccTLDs were assigned under this rule.
- su (the obsolete ISO 3166-1 code for Soviet Union; the su managers stated in 2001 they will commence accepting new su registrations, but it is unclear whether this action is compatible with ICANN policy)
- tp (the previous ISO 3166-1 code for East Timor, to be phased out in favour of tl during 2005.)
- uk (the ISO 3166-1 code for the United Kingdom is GB, however JANET had already selected UK as a top-level identifier for a pre-existing naming scheme, and this was incorporated into the top-level. gb was assigned with the intention of a transition, but this never occurred and the use of .uk is now entrenched.)
- yu (Serbia and Montenegro; the previous ISO 3166-1 code for Yugoslavia)
On September 25, 2000, ICANN decided to allow the use of any two-letter code in the ISO 3166-1 reserve list that is reserved for all purposes. Only EU (for the European Union) currently meets this criterion. Following a decision by the EU's Council of Telecommunications Ministers in March 2002, progress has been slow, but a registry (named EURid) has been chosen by the European Commission, and criteria for allocation set: the current estimate is that the eu ccTLD will be open for registrations in Autumn 2005.
There are two ccTLDs which have been deleted after the corresponding 2-letter code was withdrawn from ISO_3166-1, namely cs (for Czechoslovakia) and zr (for Zaire). There may be a significant delay between withdrawal from ISO 3166-1 and deletion from the DNS; for example, ZR ceased to be an ISO 3166-1 code in 1997, but the zr ccTLD was not deleted until 2001. Other ccTLDs corresponding to obsolete ISO 3166-1 have not yet been deleted; in some cases they may never be deleted due to the amount of disruption this would cause for a heavily used ccTLD. In particular, the Soviet Union's ccTLD su remains in use more than a decade after SU was removed from ISO 3166-1.
- IANA's list of ccTLDs - official site.
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