The right-most label conveys the top-level domain; for example, the domain name www.example.com belongs to the top-level domain com.
The hierarchy of domains descends from the right to the left label in the name; each label to the left specifies a subdivision, or subdomain of the domain to the right. For example: the label example specifies a node example.com as a subdomain of the com domain, and www is a label to create www.example.com, a subdomain of example.com. This tree of labels may consist of 127 levels. Each label may contain from 1 to 63 octets. The empty label is reserved for the root node. The full domain name may not exceed a total length of 253 ASCII characters in its textual representation.[4] In practice, some domain registries may have shorter limits.
A hostname is a domain name that has at least one associated IP address. For example, the domain names www.example.com and example.com are also hostnames, whereas the com domain is not. However, other top-level domains, particularly country code top-level domains, may indeed have an IP address, and if so, they are also hostnames.
Hostnames impose restrictions on the characters allowed in the corresponding domain name. A valid hostname is also a valid domain name, but a valid domain name may not necessarily be valid as a hostname.
Top-level domains
The top-level domains such as .com and .net and .org are the highest level of domain names of the Inteet. A top-level domain is also called a TLD. Top-level domains form the DNS root zone of the hierarchical Domain Name System. Every domain name ends in a top-level or first-level domain label.
When the Domain Name System was devised, in the 1980s, the domain name space was divided into two main groups of domains.[5] The country code top-level domains (ccTLD) were primarily based on the two-character territory codes of ISO-3166 country abbreviations. In addition, a group of seven generic top-level domains (gTLD) was implemented which represented a set of categories of names and multi-organizations.[6] These were the domains gov, edu, com, mil, org, net, and int.
During the growth of the Inteet, it became desirable to create additional generic top-level domains. As of October 2009, 21 generic top-level domains and 250 two-letter country-code top-level domains existed.[7] In addition, the ARPA domain serves technical purposes in the infrastructure of the Domain Name System.
During the 32nd Inteational Public ICANN Meeting in Paris in 2008,[8] ICANN started a new process of TLD naming policy to take a "significant step forward on the introduction of new generic top-level domains." This program envisions the availability of many new or already proposed domains, as well a new application and implementation process.[9] Observers believed that the new rules could result in hundreds of new top-level domains to be registered.[10]
IANA maintains an annotated list of top-level domains in the root zone database as well as a list of special-use (reserved) top-level domain names.
Second-level and lower level domains
Below the top-level domains in the domain name hierarchy are the second-level domain (SLD) names. These are the names directly to the left of .com, .net, and the other top-level domains. As an example, in the domain example.co.uk, co is the second-level domain.
Next are third-level domains, which are written immediately to the left of a second-level domain. There can be fourth- and fifth-level domains, and so on, with virtually no limitation. An example of an operational domain name with four levels of domain labels is www.sos.state.oh.us. The www preceding the domains is the host name of the World-Wide Web server. Each label is separated by a full stop (dot). 'sos' is said to be a sub-domain of 'state.oh.us', and 'state' a sub-domain of 'oh.us', etc. In general, subdomains are domains subordinate to their parent domain. An example of very deep levels of subdomain ordering are the IPv6 reverse resolution DNS zones, e.g. 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa, which is the reverse DNS resolution domain name for the IP address of a loopback interface, or the localhost name.
Second-level (or lower-level, depending on the established parent hierarchy) domain names are often created based on the name of a company (e.g. bbc.co.uk), product or service (e.g. hotmail.com). Below these levels, the next domain name component has been used to designate a particular host server. Therefore, ftp.wikipedia.org might be an FTP server, www.wikipedia.org would be a World Wide Web server, and mail.wikipedia.org could be an email server, each intended to perform only the implied function. Mode technology allows multiple physical servers with either different (cf. load balancing) or even identical addresses (cf. anycast) to serve a single hostname or domain name, or multiple domain names to be served by a single computer. The latter is very popular in Web hosting service centers, where service providers host the websites of many organizations on just a few servers.
The hierarchical DNS labels or components of domain names are separated in a fully qualified name by the full stop (dot, .).
Inteationalized domain names
Main article: Inteationalized domain name
The character set allowed in the Domain Name System is based on ASCII and does not allow the representation of names and words of many languages in their native scripts or alphabets. ICANN approved the Inteationalized domain name (IDNA) system, which maps Unicode strings used in application user interfaces into the valid DNS character set by an encoding called Punycode. For example, k?benhavn.eu is mapped to xn--kbenhavn-54a.eu. Many registries have adopted IDNA.
Domain name registration
History
The first commercial Inteet domain name, in the TLD .com, was registered on 15 March 1985 in the name symbolics.com by Symbolics Inc., a computer systems firm in Cambridge, Massachusetts.
By 1992, fewer than 15,000 .com domains had been registered.
In December 2009 there were 192 million domain names.[11] A large fraction of them are in the .com TLD, which as of March 15, 2010 had 84 million domain names, including 11.9 million online business and e-commerce sites, 4.3 million entertainment sites, 3.1 million finance related sites, and 1.8 million sports sites.[12] As of July 2012 the .com TLD has more registrations than all of the others combined[13]
Administration
The right to use a domain name is delegated by domain name registrars, which are accredited by the Inteet Corporation for Assigned Names and Numbers (ICANN), the organization charged with overseeing the name and number systems of the Inteet. In addition to ICANN, each top-level domain (TLD) is maintained and serviced technically by an administrative organization operating a registry. A registry is responsible for maintaining the database of names registered within the TLD it administers. The registry receives registration information from each domain name registrar authorized to assign names in the corresponding TLD and publishes the information using a special service, the whois protocol.
Registries and registrars usually charge an annual fee for the service of delegating a domain name to a user and providing a default set of name servers. Often, this transaction is termed a sale or lease of the domain name, and the registrant may sometimes be called an "owner", but no such legal relationship is actually associated with the transaction, only the exclusive right to use the domain name. More correctly, authorized users are known as "registrants" or as "domain holders".
ICANN publishes the complete list of TLD registries and domain name registrars. Registrant information associated with domain names is maintained in an online database accessible with the WHOIS service. For most of the 250 country code top-level domains (ccTLDs), the domain registries maintain the WHOIS (Registrant, name servers, expiration dates, etc.) information.
Some domain name registries, often called network information centers (NIC), also function as registrars to end-users. The major generic top-level domain registries, such as for the COM, NET, ORG, INFO domains and others, use a registry-registrar model consisting of hundreds of domain name registrars (see lists at ICANN or VeriSign). In this method of management, the registry only manages the domain name database and the relationship with the registrars. The registrants (users of a domain name) are customers of the registrar, in some cases through additional layers of resellers.
Technical requirements and process
In the process of registering a domain name and maintaining authority over the new name space created, registrars use several key pieces of information connected with a domain:
Administrative contact. A registrant usually designates an administrative contact to manage the domain name. The administrative contact usually has the highest level of control over a domain. Management functions delegated to the administrative contacts may include management of all business information, such as name of record, postal address, and contact information of the official registrant of the domain and the obligation to conform to the requirements of the domain registry in order to retain the right to use a domain name. Furthermore the administrative contact installs additional contact information for technical and billing functions.
Technical contact. The technical contact manages the name servers of a domain name. The functions of a technical contact include assuring conformance of the configurations of the domain name with the requirements of the domain registry, maintaining the domain zone records, and providing continuous functionality of the name servers (that leads to the accessibility of the domain name).
Billing contact. The party responsible for receiving billing invoices from the domain name registrar and paying applicable fees.
Name servers. Most registrars provide two or more name servers as part of the registration service. However, a registrant may specify its own authoritative name servers to host a domain's resource records. The registrar's policies gove the number of servers and the type of server information required. Some providers require a hostname and the corresponding IP address or just the hostname, which must be resolvable either in the new domain, or exist elsewhere. Based on traditional requirements (RFC 1034), typically a minimum of two servers is required.
Domain names may be formed from the set of alphanumeric ASCII characters (a-z, A-Z, 0-9), but characters are case-insensitive. In addition the hyphen is permitted if it is surrounded by a characters or digits, i.e. it is not the start or end of a label. Labels are always separated by the full stop (period) character in the textual name representation.
Business models
Domain names are often seen in analogy to real estate in that (1) domain names are foundations on which a website (like a house or commercial building) can be built and (2) the highest "quality" domain names, like sought-after real estate, tend to carry significant value, usually due to their online brand-building potential, use in advertising, search engine optimization, and many other criteria.
A few companies have offered low-cost, below-cost or even cost-free domain registrations with a variety of models adopted to recoup the costs to the provider. These usually require that domains be hosted on their website within a framework or portal that includes advertising wrapped around the domain holder's content, revenue from which allows the provider to recoup the costs. Domain registrations were free of charge when the DNS was new. A domain holder can give away or sell infinite number of subdomains under their domain name. For example, the owner of example.org could provide subdomains such as foo.example.org and foo.bar.example.org to interested parties.
Because of the popularity of the Inteet, many desirable domain names are already assigned and users must search for other acceptable names, using Web-based search features, or WHOIS and dig operating system tools. Many registrars have implemented Domain name suggestion tools which search domain name databases and suggest available alteative domain names related to keywords provided by the user.
Resale of domain names
Main article: List of most expensive domain names
The business of resale of registered domain names is known as the domain aftermarket. Various factors influence the perceived value or market value of a domain name.
Most of the million dollar domain deals are carried out privately and go unreported. As of 2011, the most expensive domain name sales on record were:
Insure.com $16 million in 2009 [14]
Fund.com 2008 £9.99 million[14]
Sex.com for $14 million in October 2010[14][15]
Po.com 2007 $9.5 million[14]
Fb.com for $8.5 million in November 2010[14][not in citation given]
Domain name confusion
Intercapping is often used to emphasize the meaning of a domain name. However, DNS names are not case-sensitive, and some names may be misinterpreted in certain uses of capitalization. For example: Who Represents, a database of artists and agents, chose whorepresents.com, which can be misread as whore presents. Similarly, a therapists' network is named therapistfinder.com. In such situations, the proper meaning may be clarified by use of hyphens in the domain name. For instance, Experts Exchange, a programmers' discussion site, for a long time used expertsexchange.com, but ultimately changed the name to experts-exchange.com.
Intellectual property entrepreneur Leo Stoller threatened to sue the owners of StealThisEmail.com on the basis that, when read as stealthisemail.com, it infringed on claimed (but invalid) trademark rights to the word "stealth".
Use in web site hosting
The domain name is a component of a Uniform Resource Locator (URL) used to access web sites, for example:
URL: http://www.example.net/index.html
Top-level domain name: net
Second-level domain name: example.net
Host name: www.example.net
A domain name may point to multiple IP addresses in order to provide server redundancy for the cybeetic services to be delivered; such multi-address capability is used to manage the traffic of large, popular web sites. More commonly, however, one server computer, at a given IP address, may also host web sites in different domains. Such address overloading enables virtual web hosting, commonly used by large web hosting services to conserve IP address space. IP-address overloading is possible through a feature in the HTTP version 1.1 protocol, but not in the HTTP version 1.0 protocol, which requires that a request identify the domain name being referred for connection.
Abuse and regulation
Critics often claim abuse of administrative power over domain names. Particularly noteworthy was the VeriSign Site Finder system which redirected all unregistered .com and .net domains to a VeriSign webpage. For example, at a public meeting with VeriSign to air technical conces about SiteFinder,[16] numerous people, active in the IETF and other technical bodies, explained how they were surprised by VeriSign's changing the fundamental behavior of a major component of Inteet infrastructure, not having obtained the customary consensus. SiteFinder, at first, assumed every Inteet query was for a website, and it monetized queries for incorrect domain names, taking the user to VeriSign's search site. Unfortunately, other applications, such as many implementations of email, treat a lack of response to a domain name query as an indication that the domain does not exist, and that the message can be treated as undeliverable. The original VeriSign implementation broke this assumption for mail, because it would always resolve an erroneous domain name to that of SiteFinder. While VeriSign later changed SiteFinder's behaviour with regard to email, there was still widespread protest about VeriSign's action being more in its financial interest than in the interest of the Inteet infrastructure component for which VeriSign was the steward.
Despite widespread criticism, VeriSign only reluctantly removed it after the Inteet Corporation for Assigned Names and Numbers (ICANN) threatened to revoke its contract to administer the root name servers. ICANN published the extensive set of letters exchanged, committee reports, and ICANN decisions.[17]
There is also significant disquiet regarding the United States' political influence over ICANN. This was a significant issue in the attempt to create a .xxx top-level domain and sparked greater interest in alteative DNS roots that would be beyond the control of any single country.[18]
Additionally, there are numerous accusations of domain name front running, whereby registrars, when given whois queries, automatically register the domain name for themselves. Network Solutions has been accused of this.[19]
طراحی وب سایت...
ما را در سایت طراحی وب سایت دنبال می کنید
برچسب : طراحی وب سایت,طراحی سایت,طراحی وب, نویسنده : keivan websara5 بازدید : 208 تاريخ : چهارشنبه 5 تير 1392 ساعت: 16:09