The Internet Assigned Numbers Authority (IANA) assigns domain identifiers such as the country code top level domain (ccTLD) which are set aside for individual national territories, or country.
IANA’s duties are not limited to the creation and delegation of identifiers, they also select relevant trustees for the ccTLD to whom the responsibility of operational administration is passed, and the assignments can be based on criteria that includes presence requirement like citizenry or other links to the ccTLD.
The ISO 3166 list is used to determine the entities that are best suitable for inclusion or not, thus it forms a basis for the country code top level domain names, the majority of ccTLD’s of ISO 3166-1 codes are under official use save for the Bouvet Island (bv) together with Svalbard and Jan Mayen (sj), they are yet to have their own assigned sub-domains regardless of their presence in the Domain Name System.
The likes of Saint Bethelemy (bl) and Saint Martin (mf) are yet to be assigned officially, the Western Sahara (eh) on the other hand does not even exist in the DNS or neither has it been assigned, despite its eligibility. The .um country code top level domain is also eligible for assignment but was removed in 2008, and it represents the United States’ minor outlying islands.
The United Kingdom today uses the .uk ISO 3166-1 code but it was initially assigned the .gb and it was never put into active use, while the East Timor code .tp was phased out in 2005 in favor of .tl, and Yugoslavia’s .yu has December 2009 as its final withdrawal deadline for new ISO 3166-1 codes – rs and .me.
All withdrawn ISO 3166-1 codes remain in the domain name system for a significant length of time before their deletion and this has been the case with former Zairean (zr) and the Czechoslovakia (cs).
The reassignment of retired codes caused a stir with certain sectors citing the ISO 3166-1 country code system’s stability and thus a 50 year blanket period for reassignments was implemented. Australia was once listed as .oz but later switched to .au and domain hacks are another form of ccTLD assignments, they involve the combination of ccTLD and second level domains that result in domains like del.icio.us (US), cr.yp.to (Tonga) and blo.gs (South Georgia and the South Sandwich Islands).
Non-country code TLD’s have also been used and these include inter.net (a generic TLD), Verisign and FSM Telecommunications entered into an agreement with small island states in the Pacific of Tuvalu and the Federated States of Micronesia to assist them in selling domain names .tv and .fm TLD’s to television and radio stations.