Historical domains

In the late 1980s InterNIC created the nato domain for use by NATO. NATO considered none of the then existing TLDs as adequately reflecting their status as an international organization. Soon after this addition, however, InterNIC also created the int TLD for the use by international organizations in general, and persuaded NATO to use the second level domain nato.int instead. The nato TLD, no longer used, was finally removed in July 1996.

Other historical TLDs are cs for Czechoslovakia (now cz for Czech Republic and sk for Slovak Republic), dd for East Germany (using de after reunification of Germany), and zr for Zaire (now cd for Democratic Republic of the Congo). In contrast to these, the TLD su has remained active despite the demise of the Soviet Union that it represents.

Reserved domains

RFC 2606 reserves the following four top-level domain names to avoid confusion and conflict.^[5] They may be used for various specific purposes however, with the intention that these should not occur in production networks within the global domain name system:

• example: reserved for use in examples
• invalid: reserved for use in obviously invalid domain names
• localhost: reserved to avoid conflict with the traditional use of localhost as a hostname
• test: reserved for use in tests

The test domain has seen usage by ICANN in the testing of internationalized domain names, a program started in 2007.^[6][7]

• xn--kgbechtv Arabic (إختبار)
• xn--hgbk6aj7f53bba Persian (آزمایشی)
• xn--0zwm56d Chinese, simplified (测试)
• xn--g6w251d Chinese, traditional (測試)
• xn--80akhbyknj4f Cyrillic (испытание)
• xn--11b5bs3a9aj6g Hindi (परीक्षा)
• xn--jxalpdlp Greek (δοκιμή)
• xn--9t4b11yi5a Korean (테스트)
• xn--deba0ad Yiddish (טעסט)
• xn--zckzah Japanese (テスト)
• xn--hlcj6aya9esc7a Tamil (பரிட்சை)

Infrastructure domain

The domain arpa was the first Internet top-level domain. It was intended to be used only temporarily, aiding in the transition of traditional ARPANET host names to the domain name system. However, after it had been used for reverse DNS lookup, it was found impractical to retire it, and is used today exclusively for Internet infrastructure purposes such as in-addr.arpa for IPv4 and ip6.arpa for IPv6 reverse DNS resolution, uri.arpa and urn.arpa for the Dynamic Delegation Discovery System, and e164.arpa for telephone number mapping based on NAPTR DNS records. For historical reasons, arpa is sometimes considered to be a generic top-level domain.

Top-level domain

A top-level domain or domain name (TLD) is the highest level of domain names in the root zone of the Domain Name System of the Internet. For all domains in lower levels, it is the last part of the domain name, that is, the label that follows the last dot of a fully qualified domain name. For example, in the domain name www.example.com, the top-level domain is com, or COM, as domain names are not case-sensitive. Management of most top-level domains is delegated to responsible organizations by the Internet Corporation for Assigned Names and Numbers (ICANN), which operates the Internet Assigned Numbers Authority (IANA) and is in charge of maintaining the DNS root zone.

Originally, the top-level domain space was organized into three main groups,^[1] Countries, Categories, and Multiorganizations. An additional temporary group consisted only of the initial DNS domain,^[2] arpa, intended for transitional purposes toward the stabilization of the domain name system.

Countries are designated in the domain name system by their English two-letter ISO country code^[3]. This group of domains is therefore commonly known as country-code top-level domains (ccTLD).

The Categories group has become known as the generic top-level domains. Initially this group consisted of GOV, EDU, COM, MIL, ORG, and NET.

In the growth of the Internet, it became desirable to create additional generic top-level domains. Some of the initial domains' purposes were also generalized, modified, or assigned for maintanance to special organizations affiliated with the intended purpose.

As a result, IANA today distinguishes the following groups of top-level domains:^[4]

• country-code top-level domains (ccTLD): Two letter domains established for countries or territories. With some historical exceptions, the code for any territory is the same as its two-letter ISO 3166 code.
• generic top-level domains (gTLD): Top-level domains with three or more characters
  • unsponsored top-level domains: domains that operate directly under policies established by ICANN processes for the global Internet community.
  • sponsored top-level domains (sTLD): These domains are proposed and sponsored by private agencies or organizations that establish and enforce rules restricting the eligibility to use the TLD. Use is based on community theme concepts.
  • infrastructure top-level domain: This group consists of one domain, the Address and Routing Parameter Area (ARPA). It is managed by IANA on behalf of the Internet Engineering Task Force for various purposes specified in Request for Comments.

Generic TLDs

In the 1980s, seven gTLDs (.com, .edu, .gov, .int, .mil, .net, and .org) were created. Domain names may be registered in three of these (.com, .net, and .org) without restriction; the other four have limited purposes.

In years following the creation of the original gTLDs, various discussions occurred concerning additional gTLDs, leading to the selection in November 2000 of seven new TLDs for introduction. These were introduced in 2001 and 2002. Four of the new TLDs (.biz, .info, .name, and .pro) are unsponsored. The other three new TLDs (.aero, .coop, and .museum) are sponsored. In 2003, ICANN initiated a process that resulted in the introduction of six new TLDs (.asia, .cat, .jobs, .mobi, .tel and .travel) that are sponsored. Information about that process may be found here.

Generally speaking, an unsponsored TLD operates under policies established by the global Internet community directly through the ICANN process, while a sponsored TLD is a specialized TLD that has a sponsor representing the narrower community that is most affected by the TLD. The sponsor thus carries out delegated policy-formulation responsibilities over many matters concerning the TLD.

A Sponsor is an organization to which is delegated some defined ongoing policy-formulation authority regarding the manner in which a particular sponsored TLD is operated. The sponsored TLD has a Charter, which defines the purpose for which the sponsored TLD has been created and will be operated. The Sponsor is responsible for developing policies on the delegated topics so that the TLD is operated for the benefit of a defined group of stakeholders, known as the Sponsored TLD Community, that are most directly interested in the operation of the TLD. The Sponsor also is responsible for selecting the registry operator and to varying degrees for establishing the roles played by registrars and their relationship with the registry operator. The Sponsor must exercise its delegated authority according to fairness standards and in a manner that is representative of the Sponsored TLD Community.

The extent to which policy-formulation responsibilities are appropriately delegated to a Sponsor depends upon the characteristics of the organization that may make such delegation appropriate. These characteristics may include the mechanisms the organization uses to formulate policies, its mission, its guarantees of independence from the registry operator and registrars, who will be permitted to participate in the Sponsor's policy-development efforts and in what way, and the Sponsor's degree and type of accountability to the Sponsored TLD Community.

Top-Level Domains (gTLDs)

Introduction

The Internet's domain-name system (DNS) allows users to refer to web sites and other resources using easier-to-remember domain names (such as "www.icann.org") rather than the all-numeric IP addresses (such as "192.0.34.65") assigned to each computer on the Internet. Each domain name is made up of a series of character strings (called "labels") separated by dots. The right-most label in a domain name is referred to as its "top-level domain" (TLD).

The DNS forms a tree-like hierarchy. Each TLD includes many second-level domains (such as "icann" in "www.icann.org"); each second-level domain can include a number of third-level domains ("www" in "www.icann.org"), and so on.

The responsibility for operating each TLD (including maintaining a registry of the second-level domains within the TLD) is delegated to a particular organization. These organizations are referred to as "registry operators", "sponsors", or simply "delegees."

There are several types of TLDs within the DNS:

• TLDs with two letters (such as .de, .mx, and .jp) have been established for over 250 countries and external territories and are referred to as "country-code" TLDs or "ccTLDs". They are delegated to designated managers, who operate the ccTLDs according to local policies that are adapted to best meet the economic, cultural, linguistic, and legal circumstances of the country or territory involved. For more details, see the ccTLD web page on the IANA web site.
• Most TLDs with three or more characters are referred to as "generic" TLDs, or "gTLDs". They can be subdivided into two types, "sponsored" TLDs (sTLDs) and "unsponsored TLDs (uTLDs), as described in more detail below.
• In addition to gTLDs and ccTLDs, there is one special TLD, .arpa, which is used for technical infrastructure purposes. ICANN administers the .arpa TLD in cooperation with the Internet technical community under the guidance of the Internet Architecture Board.

Virtual private server

A virtual private server (VPS, also referred to as Virtual Dedicated Server or VDS) is a method of partitioning a physical server computer into multiple servers such that each has the appearance and capabilities of running on its own dedicated machine. Each virtual server can run its own full-fledged operating system, and each server can be independently rebooted.

The practice of partitioning a single server so that it appears as multiple servers has long been common practice in mainframe computers, but has seen a resurgence lately with the development of virtualization software and technologies for other architectures.

The physical server boots normally. It then runs a program that boots each virtual server within a virtualization environment (similar to an emulator). The virtual servers have no direct access to hardware and are usually booted from a disk image.

There are two kinds of virtualizations: software based and hardware based. In a software based virtualization environment, the virtual machines share the same kernel and actually require the main node's resources. This kind of virtualization normally has many benefits in a web hosting environment because of quota incrementing and decrementing in real time with no need of restarting the node. The main examples are Xen, Virtuozzo, Vserver, and OpenVZ (which is the open source and development version of Parallels Virtuozzo Containers).

In a hardware based virtualization, the virtualization mechanism partitions the real hardware resources. In typical implementations, no burst and/or realtime quota modification is possible; the limits are hard and can only be modified by restarting a virtual machine instance^{[citation needed]}. This kind of environment is potentially more secure in the sense that it is less subject to "Quality of Service crosstalk" between VM instances^{[citation needed]}; on the other hand, its security is typically dependent on the correctness of a larger and more complicated Trusted Computing Base^{[citation needed]}. It is more commonly used in enterprise/commercial deployments^{[citation needed]}. Examples include Microsoft Virtual Server, VMware ESX Server, and Xen.