Imagine that everybody in the world used their Social Security number or their telephone number instead of their name... If names didn't exist, you'd be forced to invent them, or you'd never be able to identify your closest friends, let alone casual acquaintances you'd met only a couple of times!
Domain names were invented to fill a similar need on the Internet. Most computers connected to the Internet are identified by a unique number called an IP address (for instance, 234.208.12.129). IP addresses are neither intuitive (they don't correspond to a geographical location) nor easy to remember (you can prove that by glancing away from this page and then trying to quote the example IP address above!)
If you type the IP address into the URL bar of your browser you will be taken to the web site it relates to. As well as being hard to remember, however, IP addresses are also FIXED (i.e. if you change web hosting companies you'll need to get a new IP address for your site).
Domain names offer a more intuitive way to name and find a website. Each domain name replaces a string of meaningless numbers (an IP address) with a simple word or expression. That's the theory - in practice, domain names can be pretty obscure too.
The Structure of a Domain NameLet's look in more detail at a domain name, using this site's domain name as an example. This site's domain name is igoldrush.com - you can check this easily by looking at in the URL or location bar of your browser.
.com is the top domain under which my domain name is registered. There are heaps of different top domains out there, from commercial (.com) through to non-profit (.org) and even country-specific top domains such as France (.fr) and Italy (.it). Every domain name is registered under a top domain of some kind. The top domain is often known as the domain extension - these are the same thing, so don't get mixed up!
วันศุกร์ที่ 10 สิงหาคม พ.ศ. 2550
What is Domain Registration?
Domain registration is the process by which a company or individual can secure a website domain, such as www.yoursite.com. Once you have completed domain registration the domain becomes yours for the period of the contract, usually one year. Before registration expires it must be renewed, or the domain reverts back to being available to the general public.
The Internet Corporation for Assigned Names and Numbers (ICANN) manages the international Domain Name Server (DNS) database. ICANN insures that all registered names are unique and map properly to a unique Internet Protocol (IP) address. The IP address is the numerical address of the website that tells other computers on the Internet where to find the server host and domain.
Domain registration is available to the public via a registrar. Fees and services vary from company to company, but the process is generally inexpensive. Before a domain registration can be approved, the new name must be checked against existing names in the DNS database. The online registrar provides a field into which you can enter your desired name and hierarchy —- that is, the letters that come after the "dot." Familiar hierarchies are .com, .net, .org, .name, .info and .biz. If the name is not already taken, it is available for domain registration.
During the domain registration process, you will be required to give contact information that will be publicly available through the WHOIS database. Anyone can go to a WHOIS search engine and enter a domain name to see who has registered it. Registrars require that this information be accurate and true. If you feel uncomfortable providing personal information, there are some registrars that will act as your proxy, supplying their information in place of your own as the contact for the domain. There may be a small fee for this service and potential drawbacks to balance against the ability to maintain your privacy, so read the Terms and Conditions carefully before deciding to opt for a domain by proxy.
Also important, be sure you will own the domain name, as some registrars maintain control over the domains they register. And be sure you retain the option to transfer the domain to another registrar, if you wish. There might be an initial period after which this becomes possible. Look for any fees that might be incurred as a result of transferring the domain. This could become important down the road if you wish to take advantage of another registrar's products or services.
Upon completing the domain registration process, it will take a period of hours to a few days to be able to see the domain online. The domain can be "parked" with an "in construction" page that acts as a kind of placeholder. Parking a domain is very inexpensive and most registrars offer this service for a small fee to give you time to come up with content. Once a registrant is ready to supply content, a web server must host the domain. The registrar might also provide hosting services, or you may wish to transfer your domain to another web hosting company.
If you are considering domain registration, ICANN recommends dealing with an accredited registrar. These registrars have entered into an official agreement with ICANN to meet minimal requirements for providing domain registration. For more information about domain registration, and for a list of accredited registrars
The Internet Corporation for Assigned Names and Numbers (ICANN) manages the international Domain Name Server (DNS) database. ICANN insures that all registered names are unique and map properly to a unique Internet Protocol (IP) address. The IP address is the numerical address of the website that tells other computers on the Internet where to find the server host and domain.
Domain registration is available to the public via a registrar. Fees and services vary from company to company, but the process is generally inexpensive. Before a domain registration can be approved, the new name must be checked against existing names in the DNS database. The online registrar provides a field into which you can enter your desired name and hierarchy —- that is, the letters that come after the "dot." Familiar hierarchies are .com, .net, .org, .name, .info and .biz. If the name is not already taken, it is available for domain registration.
During the domain registration process, you will be required to give contact information that will be publicly available through the WHOIS database. Anyone can go to a WHOIS search engine and enter a domain name to see who has registered it. Registrars require that this information be accurate and true. If you feel uncomfortable providing personal information, there are some registrars that will act as your proxy, supplying their information in place of your own as the contact for the domain. There may be a small fee for this service and potential drawbacks to balance against the ability to maintain your privacy, so read the Terms and Conditions carefully before deciding to opt for a domain by proxy.
Also important, be sure you will own the domain name, as some registrars maintain control over the domains they register. And be sure you retain the option to transfer the domain to another registrar, if you wish. There might be an initial period after which this becomes possible. Look for any fees that might be incurred as a result of transferring the domain. This could become important down the road if you wish to take advantage of another registrar's products or services.
Upon completing the domain registration process, it will take a period of hours to a few days to be able to see the domain online. The domain can be "parked" with an "in construction" page that acts as a kind of placeholder. Parking a domain is very inexpensive and most registrars offer this service for a small fee to give you time to come up with content. Once a registrant is ready to supply content, a web server must host the domain. The registrar might also provide hosting services, or you may wish to transfer your domain to another web hosting company.
If you are considering domain registration, ICANN recommends dealing with an accredited registrar. These registrars have entered into an official agreement with ICANN to meet minimal requirements for providing domain registration. For more information about domain registration, and for a list of accredited registrars
Domain name system
From Wikipedia, the free encyclopedia
“DNS” redirects here. For other uses, see DNS (disambiguation).
On the Internet, the Domain Name System (DNS) associates various sorts of information with so-called domain names; most importantly, it serves as the "phone book" for the Internet: it translates human-readable computer hostnames, e.g. en.wikipedia.org, into the IP addresses that networking equipment needs for delivering information. It also stores other information such as the list of mail exchange servers that accept email for a given domain. In providing a worldwide keyword-based redirection service, the Domain Name System is an essential component of contemporary Internet use.
Uses
The most basic use of DNS is to translate hostnames to IP addresses. It is in very simple terms like a phone book. For example, if you want to know the internet address of en.wikipedia.org, the Domain Name System can be used to tell you it is 66.230.200.100. DNS also has other important uses.
Pre-eminently, DNS makes it possible to assign Internet destinations to the human organization or concern they represent, independently of the physical routing hierarchy represented by the numerical IP address. Because of this, hyperlinks and Internet contact information can remain the same, whatever the current IP routing arrangements may be, and can take a human-readable form (such as "wikipedia.org") which is rather easier to remember than an IP address (such as 66.230.200.100). People take advantage of this when they recite meaningful URLs and e-mail addresses without caring how the machine will actually locate them.
The Domain Name System distributes the responsibility for assigning domain names and mapping them to IP networks by allowing an authoritative server for each domain to keep track of its own changes, avoiding the need for a central registrar to be continually consulted and updated.
History
The practice of using a name as a more human-legible abstraction of a machine's numerical address on the network predates even TCP/IP, and goes all the way to the ARPAnet era. Back then however, a different system was used, as DNS was only invented in 1983, shortly after TCP/IP was deployed. With the older system, each computer on the network retrieved a file called HOSTS.TXT from a computer at SRI (now SRI International). The HOSTS.TXT file mapped numerical addresses to names. A hosts file still exists on most modern operating systems, either by default or through configuration, and allows users to specify an IP address (eg. 192.0.34.166) to use for a hostname (eg. http://en.wikipedia.org/wiki/Example.net) without checking DNS. As of 2006, the hosts file serves primarily for troubleshooting DNS errors or for mapping local addresses to more organic names. Systems based on a hosts file have inherent limitations, because of the obvious requirement that every time a given computer's address changed, every computer that seeks to communicate with it would need an update to its hosts file.
The growth of networking called for a more scalable system: one that recorded a change in a host's address in one place only. Other hosts would learn about the change dynamically through a notification system, thus completing a globally accessible network of all hosts' names and their associated IP Addresses.
At the request of Jon Postel, Paul Mockapetris invented the Domain Name System in 1983 and wrote the first implementation. The original specifications appear in RFC 882 and 883. In 1987, the publication of RFC 1034 and RFC 1035 updated the DNS specification and made RFC 882 and RFC 883 obsolete. Several more-recent RFCs have proposed various extensions to the core DNS protocols.
In 1984, four Berkeley students — Douglas Terry, Mark Painter, David Riggle and Songnian Zhou — wrote the first UNIX implementation, which was maintained by Ralph Campbell thereafter. In 1985, Kevin Dunlap of DEC significantly re-wrote the DNS implementation and renamed it BIND (Berkeley Internet Name Domain, previously: Berkeley Internet Name Daemon). Mike Karels, Phil Almquist and Paul Vixie have maintained BIND since then. BIND was ported to the Windows NT platform in the early 1990s.
Due to BIND's long history of security issues and exploits, several alternative nameserver/resolver programs have been written and distributed in recent years.
How DNS works in theory
The domain name space consists of a tree of domain names. Each node or leaf in the tree has one or more resource records, which hold information associated with the domain name. The tree sub-divides into zones. A zone consists of a collection of connected nodes authoritatively served by an authoritative DNS nameserver. (Note that a single nameserver can host several zones.)
When a system administrator wants to let another administrator control a part of the domain name space within his or her zone of authority, he or she can delegate control to the other administrator. This splits a part of the old zone off into a new zone, which comes under the authority of the second administrator's nameservers. The old zone becomes no longer authoritative for what goes under the authority of the new zone.
A resolver looks up the information associated with nodes. A resolver knows how to communicate with name servers by sending DNS requests, and heeding DNS responses. Resolving usually entails iterating through several name servers to find the needed information.
Some resolvers function simplistically and can only communicate with a single name server. These simple resolvers rely on a recursing name server to perform the work of finding information for them.
Parts of a domain name
A domain name usually consists of two or more parts (technically labels), separated by dots. For example wikipedia.org.
The rightmost label conveys the top-level domain (for example, the address en.wikipedia.org has the top-level domain org).
Each label to the left specifies a subdivision or subdomain of the domain above it. Note that "subdomain" expresses relative dependence, not absolute dependence: for example, wikipedia.org comprises a subdomain of the org domain, and en.wikipedia.org comprises a subdomain of the domain wikipedia.org. In theory, this subdivision can go down to 127 levels deep, and each label can contain up to 63 characters, as long as the whole domain name does not exceed a total length of 255 characters. But in practice some domain registries have shorter limits than that.
A hostname refers to a domain name that has one or more associated IP addresses. For example, the en.wikipedia.org and wikipedia.org domains are both hostnames, but the org domain is not.
The Domain Name System consists of a hierarchical set of DNS servers. Each domain or subdomain has one or more authoritative DNS servers that publish information about that domain and the name servers of any domains "beneath" it. The hierarchy of authoritative DNS servers matches the hierarchy of domains. At the top of the hierarchy stand the root nameservers: the servers to query when looking up (resolving) a top-level domain name (TLD).
Iterative and recursive queries:
An Iterative query is one where the DNS server may provide a partial answer to the query (or give an error). DNS servers must support non-recursive queries.
A recursive query is one where the DNS server will fully answer the query (or give an error). DNS servers are not required to support recursive queries and both the resolver (or another DNS acting recursively on behalf of another resolver) negotiate use of recursive service using bits in the query headers.
Address resolution mechanism
(This description deliberately uses the fictional .example TLD in accordance with the DNS guidelines themselves.)
In theory a full host name may have several name segments, (e.g ahost.ofasubnet.ofabiggernet.inadomain.example). In practice, in the experience of the majority of public users of Internet services, full host names will frequently consist of just three segments (ahost.inadomain.example, and most often www.inadomain.example).
For querying purposes, software interprets the name segment by segment, from right to left, using an iterative search procedure. At each step along the way, the program queries a corresponding DNS server to provide a pointer to the next server which it should consult.
As originally envisaged, the process was as simple as:
the local system is pre-configured with the known addresses of the root servers in a file of root hints, which need to be updated periodically by the local administrator from a reliable source to be kept up to date with the changes which occur over time.
query one of the root servers to find the server authoritative for the next level down (so in the case of our simple hostname, a root server would be asked for the address of a server with detailed knowledge of the example top level domain).
querying this second server for the address of a DNS server with detailed knowledge of the second-level domain (inadomain.example in our example).
repeating the previous step to progress down the name, until the final step which would, rather than generating the address of the next DNS server, return the final address sought.
The diagram illustrates this process for the real host www.wikipedia.org.
The mechanism in this simple form has a difficulty: it places a huge operating burden on the root servers, with each and every search for an address starting by querying one of them. Being as critical as they are to the overall function of the system such heavy use would create an insurmountable bottleneck for trillions of queries placed every day. The section DNS in practice describes how this is addressed.
Circular dependencies and glue records
Name servers in delegations appear listed by name, rather than by IP address. This means that a resolving name server must issue another DNS request to find out the IP address of the server to which it has been referred. Since this can introduce a circular dependency if the nameserver referred to is under the domain that it is authoritative of, it is occasionally necessary for the nameserver providing the delegation to also provide the IP address of the next nameserver. This record is called a glue record.
For example, assume that the sub-domain en.wikipedia.org contains further sub-domains (such as something.en.wikipedia.org) and that the authoritative nameserver for these lives at ns1.en.wikipedia.org. A computer trying to resolve something.en.wikipedia.org will thus first have to resolve ns1.en.wikipedia.org. Since ns1 is also under the en.wikipedia.org subdomain, resolving ns1.en.wikipedia.org requires resolving ns1.en.wikipedia.org which is exactly the circular dependency mentioned above. The dependency is broken by the glue record in the nameserver of wikipedia.org that provides the IP address of ns1.en.wikipedia.org directly to the requestor, enabling it to bootstrap the process by figuring out where ns1.en.wikipedia.org is located.
In practice
When an application (such as a web browser) tries to find the IP address of a domain name, it doesn't necessarily follow all of the steps outlined in the Theory section above. We will first look at the concept of caching, and then outline the operation of DNS in "the real world."
Caching and time to live
Because of the huge volume of requests generated by a system like DNS, the designers wished to provide a mechanism to reduce the load on individual DNS servers. To this end, the DNS resolution process allows for caching (ie. the local recording and subsequent consultation of the results of a DNS query) for a given period of time after a successful answer. How long a resolver caches a DNS response (ie. how long a DNS response remains valid) is determined by a value called the time to live (TTL). The TTL is set by the administrator of the DNS server handing out the response. The period of validity may vary from just seconds to days or even weeks.
Caching time
As a noteworthy consequence of this distributed and caching architecture, changes to DNS do not always take effect immediately and globally. This is best explained with an example: If an administrator has set a TTL of 6 hours for the host www.wikipedia.org, and then changes the IP address to which www.wikipedia.org resolves at 12:01pm, the administrator must consider that a person who cached a response with the old IP address at 12:00pm will not consult the DNS server again until 6:00pm. The period between 12:01pm and 6:00pm in this example is called caching time, which is best defined as a period of time that begins when you make a change to a DNS record and ends after the maximum amount of time specified by the TTL expires. This essentially leads to an important logistical consideration when making changes to DNS: not everyone is necessarily seeing the same thing you're seeing. RFC 1537 helps to convey basic rules for how to set the TTL.
Note that the term "propagation", although very widely used in this context, does not describe the effects of caching well. Specifically, it implies that [1] when you make a DNS change, it somehow spreads to all other DNS servers (instead, other DNS servers check in with yours as needed), and [2] that you do not have control over the amount of time the record is cached (you control the TTL values for all DNS records in your domain, except your NS records and any authoritative DNS servers that use your domain name).
Some resolvers may override TTL values, as the protocol supports caching for up to 68 years or no caching at all. Negative caching (the non-existence of records) is determined by name servers authoritative for a zone which MUST include the SOA record when reporting no data of the requested type exists. The MINIMUM field of the SOA record and the TTL of the SOA itself is used to establish the TTL for the negative answer. RFC 2308
Many people incorrectly refer to a mysterious 48 hour or 72 hour propagation time when you make a DNS change. When one changes the NS records for one's domain or the IP addresses for hostnames of authoritative DNS servers using one's domain (if any), there can be a lengthy period of time before all DNS servers use the new information. This is because those records are handled by the zone parent DNS servers (for example, the .com DNS servers if your domain is example.com), which typically cache those records for 48 hours. However, those DNS changes will be immediately available for any DNS servers that do not have them cached. And, any DNS changes on your domain other than the NS records and authoritative DNS server names can be nearly instantaneous, if you choose for them to be (by lowering the TTL once or twice ahead of time, and waiting until the old TTL expires before making the change).
In the real world
“DNS” redirects here. For other uses, see DNS (disambiguation).
On the Internet, the Domain Name System (DNS) associates various sorts of information with so-called domain names; most importantly, it serves as the "phone book" for the Internet: it translates human-readable computer hostnames, e.g. en.wikipedia.org, into the IP addresses that networking equipment needs for delivering information. It also stores other information such as the list of mail exchange servers that accept email for a given domain. In providing a worldwide keyword-based redirection service, the Domain Name System is an essential component of contemporary Internet use.
Uses
The most basic use of DNS is to translate hostnames to IP addresses. It is in very simple terms like a phone book. For example, if you want to know the internet address of en.wikipedia.org, the Domain Name System can be used to tell you it is 66.230.200.100. DNS also has other important uses.
Pre-eminently, DNS makes it possible to assign Internet destinations to the human organization or concern they represent, independently of the physical routing hierarchy represented by the numerical IP address. Because of this, hyperlinks and Internet contact information can remain the same, whatever the current IP routing arrangements may be, and can take a human-readable form (such as "wikipedia.org") which is rather easier to remember than an IP address (such as 66.230.200.100). People take advantage of this when they recite meaningful URLs and e-mail addresses without caring how the machine will actually locate them.
The Domain Name System distributes the responsibility for assigning domain names and mapping them to IP networks by allowing an authoritative server for each domain to keep track of its own changes, avoiding the need for a central registrar to be continually consulted and updated.
History
The practice of using a name as a more human-legible abstraction of a machine's numerical address on the network predates even TCP/IP, and goes all the way to the ARPAnet era. Back then however, a different system was used, as DNS was only invented in 1983, shortly after TCP/IP was deployed. With the older system, each computer on the network retrieved a file called HOSTS.TXT from a computer at SRI (now SRI International). The HOSTS.TXT file mapped numerical addresses to names. A hosts file still exists on most modern operating systems, either by default or through configuration, and allows users to specify an IP address (eg. 192.0.34.166) to use for a hostname (eg. http://en.wikipedia.org/wiki/Example.net) without checking DNS. As of 2006, the hosts file serves primarily for troubleshooting DNS errors or for mapping local addresses to more organic names. Systems based on a hosts file have inherent limitations, because of the obvious requirement that every time a given computer's address changed, every computer that seeks to communicate with it would need an update to its hosts file.
The growth of networking called for a more scalable system: one that recorded a change in a host's address in one place only. Other hosts would learn about the change dynamically through a notification system, thus completing a globally accessible network of all hosts' names and their associated IP Addresses.
At the request of Jon Postel, Paul Mockapetris invented the Domain Name System in 1983 and wrote the first implementation. The original specifications appear in RFC 882 and 883. In 1987, the publication of RFC 1034 and RFC 1035 updated the DNS specification and made RFC 882 and RFC 883 obsolete. Several more-recent RFCs have proposed various extensions to the core DNS protocols.
In 1984, four Berkeley students — Douglas Terry, Mark Painter, David Riggle and Songnian Zhou — wrote the first UNIX implementation, which was maintained by Ralph Campbell thereafter. In 1985, Kevin Dunlap of DEC significantly re-wrote the DNS implementation and renamed it BIND (Berkeley Internet Name Domain, previously: Berkeley Internet Name Daemon). Mike Karels, Phil Almquist and Paul Vixie have maintained BIND since then. BIND was ported to the Windows NT platform in the early 1990s.
Due to BIND's long history of security issues and exploits, several alternative nameserver/resolver programs have been written and distributed in recent years.
How DNS works in theory
The domain name space consists of a tree of domain names. Each node or leaf in the tree has one or more resource records, which hold information associated with the domain name. The tree sub-divides into zones. A zone consists of a collection of connected nodes authoritatively served by an authoritative DNS nameserver. (Note that a single nameserver can host several zones.)
When a system administrator wants to let another administrator control a part of the domain name space within his or her zone of authority, he or she can delegate control to the other administrator. This splits a part of the old zone off into a new zone, which comes under the authority of the second administrator's nameservers. The old zone becomes no longer authoritative for what goes under the authority of the new zone.
A resolver looks up the information associated with nodes. A resolver knows how to communicate with name servers by sending DNS requests, and heeding DNS responses. Resolving usually entails iterating through several name servers to find the needed information.
Some resolvers function simplistically and can only communicate with a single name server. These simple resolvers rely on a recursing name server to perform the work of finding information for them.
Parts of a domain name
A domain name usually consists of two or more parts (technically labels), separated by dots. For example wikipedia.org.
The rightmost label conveys the top-level domain (for example, the address en.wikipedia.org has the top-level domain org).
Each label to the left specifies a subdivision or subdomain of the domain above it. Note that "subdomain" expresses relative dependence, not absolute dependence: for example, wikipedia.org comprises a subdomain of the org domain, and en.wikipedia.org comprises a subdomain of the domain wikipedia.org. In theory, this subdivision can go down to 127 levels deep, and each label can contain up to 63 characters, as long as the whole domain name does not exceed a total length of 255 characters. But in practice some domain registries have shorter limits than that.
A hostname refers to a domain name that has one or more associated IP addresses. For example, the en.wikipedia.org and wikipedia.org domains are both hostnames, but the org domain is not.
The Domain Name System consists of a hierarchical set of DNS servers. Each domain or subdomain has one or more authoritative DNS servers that publish information about that domain and the name servers of any domains "beneath" it. The hierarchy of authoritative DNS servers matches the hierarchy of domains. At the top of the hierarchy stand the root nameservers: the servers to query when looking up (resolving) a top-level domain name (TLD).
Iterative and recursive queries:
An Iterative query is one where the DNS server may provide a partial answer to the query (or give an error). DNS servers must support non-recursive queries.
A recursive query is one where the DNS server will fully answer the query (or give an error). DNS servers are not required to support recursive queries and both the resolver (or another DNS acting recursively on behalf of another resolver) negotiate use of recursive service using bits in the query headers.
Address resolution mechanism
(This description deliberately uses the fictional .example TLD in accordance with the DNS guidelines themselves.)
In theory a full host name may have several name segments, (e.g ahost.ofasubnet.ofabiggernet.inadomain.example). In practice, in the experience of the majority of public users of Internet services, full host names will frequently consist of just three segments (ahost.inadomain.example, and most often www.inadomain.example).
For querying purposes, software interprets the name segment by segment, from right to left, using an iterative search procedure. At each step along the way, the program queries a corresponding DNS server to provide a pointer to the next server which it should consult.
As originally envisaged, the process was as simple as:
the local system is pre-configured with the known addresses of the root servers in a file of root hints, which need to be updated periodically by the local administrator from a reliable source to be kept up to date with the changes which occur over time.
query one of the root servers to find the server authoritative for the next level down (so in the case of our simple hostname, a root server would be asked for the address of a server with detailed knowledge of the example top level domain).
querying this second server for the address of a DNS server with detailed knowledge of the second-level domain (inadomain.example in our example).
repeating the previous step to progress down the name, until the final step which would, rather than generating the address of the next DNS server, return the final address sought.
The diagram illustrates this process for the real host www.wikipedia.org.
The mechanism in this simple form has a difficulty: it places a huge operating burden on the root servers, with each and every search for an address starting by querying one of them. Being as critical as they are to the overall function of the system such heavy use would create an insurmountable bottleneck for trillions of queries placed every day. The section DNS in practice describes how this is addressed.
Circular dependencies and glue records
Name servers in delegations appear listed by name, rather than by IP address. This means that a resolving name server must issue another DNS request to find out the IP address of the server to which it has been referred. Since this can introduce a circular dependency if the nameserver referred to is under the domain that it is authoritative of, it is occasionally necessary for the nameserver providing the delegation to also provide the IP address of the next nameserver. This record is called a glue record.
For example, assume that the sub-domain en.wikipedia.org contains further sub-domains (such as something.en.wikipedia.org) and that the authoritative nameserver for these lives at ns1.en.wikipedia.org. A computer trying to resolve something.en.wikipedia.org will thus first have to resolve ns1.en.wikipedia.org. Since ns1 is also under the en.wikipedia.org subdomain, resolving ns1.en.wikipedia.org requires resolving ns1.en.wikipedia.org which is exactly the circular dependency mentioned above. The dependency is broken by the glue record in the nameserver of wikipedia.org that provides the IP address of ns1.en.wikipedia.org directly to the requestor, enabling it to bootstrap the process by figuring out where ns1.en.wikipedia.org is located.
In practice
When an application (such as a web browser) tries to find the IP address of a domain name, it doesn't necessarily follow all of the steps outlined in the Theory section above. We will first look at the concept of caching, and then outline the operation of DNS in "the real world."
Caching and time to live
Because of the huge volume of requests generated by a system like DNS, the designers wished to provide a mechanism to reduce the load on individual DNS servers. To this end, the DNS resolution process allows for caching (ie. the local recording and subsequent consultation of the results of a DNS query) for a given period of time after a successful answer. How long a resolver caches a DNS response (ie. how long a DNS response remains valid) is determined by a value called the time to live (TTL). The TTL is set by the administrator of the DNS server handing out the response. The period of validity may vary from just seconds to days or even weeks.
Caching time
As a noteworthy consequence of this distributed and caching architecture, changes to DNS do not always take effect immediately and globally. This is best explained with an example: If an administrator has set a TTL of 6 hours for the host www.wikipedia.org, and then changes the IP address to which www.wikipedia.org resolves at 12:01pm, the administrator must consider that a person who cached a response with the old IP address at 12:00pm will not consult the DNS server again until 6:00pm. The period between 12:01pm and 6:00pm in this example is called caching time, which is best defined as a period of time that begins when you make a change to a DNS record and ends after the maximum amount of time specified by the TTL expires. This essentially leads to an important logistical consideration when making changes to DNS: not everyone is necessarily seeing the same thing you're seeing. RFC 1537 helps to convey basic rules for how to set the TTL.
Note that the term "propagation", although very widely used in this context, does not describe the effects of caching well. Specifically, it implies that [1] when you make a DNS change, it somehow spreads to all other DNS servers (instead, other DNS servers check in with yours as needed), and [2] that you do not have control over the amount of time the record is cached (you control the TTL values for all DNS records in your domain, except your NS records and any authoritative DNS servers that use your domain name).
Some resolvers may override TTL values, as the protocol supports caching for up to 68 years or no caching at all. Negative caching (the non-existence of records) is determined by name servers authoritative for a zone which MUST include the SOA record when reporting no data of the requested type exists. The MINIMUM field of the SOA record and the TTL of the SOA itself is used to establish the TTL for the negative answer. RFC 2308
Many people incorrectly refer to a mysterious 48 hour or 72 hour propagation time when you make a DNS change. When one changes the NS records for one's domain or the IP addresses for hostnames of authoritative DNS servers using one's domain (if any), there can be a lengthy period of time before all DNS servers use the new information. This is because those records are handled by the zone parent DNS servers (for example, the .com DNS servers if your domain is example.com), which typically cache those records for 48 hours. However, those DNS changes will be immediately available for any DNS servers that do not have them cached. And, any DNS changes on your domain other than the NS records and authoritative DNS server names can be nearly instantaneous, if you choose for them to be (by lowering the TTL once or twice ahead of time, and waiting until the old TTL expires before making the change).
In the real world
Users generally do not communicate directly with a DNS resolver. Instead DNS resolution takes place transparently in client applications such as web browsers, mail clients, and other Internet applications. When a request is made which necessitates a DNS lookup, such programs send a resolution request to the local DNS resolver in the operating system which in turn handles the communications required.
The DNS resolver will almost invariably have a cache (see above) containing recent lookups. If the cache can provide the answer to the request, the resolver will return the value in the cache to the program that made the request. If the cache does not contain the answer, the resolver will send the request to a designated DNS server or servers. In the case of most home users, the Internet service provider to which the machine connects will usually supply this DNS server: such a user will either have configured that server's address manually or allowed DHCP to set it; however, where systems administrators have configured systems to use their own DNS servers, their DNS resolvers point to separately maintained nameservers of the organization. In any event, the name server thus queried will follow the process outlined above, until it either successfully finds a result or does not. It then returns its results to the DNS resolver; assuming it has found a result, the resolver duly caches that result for future use, and hands the result back to the software which initiated the request.
Broken resolvers
An additional level of complexity emerges when resolvers violate the rules of the DNS protocol. Some people have suggested[citation needed] that a number of large ISPs have configured their DNS servers to violate rules (presumably to allow them to run on less-expensive hardware than a fully compliant resolver), such as by disobeying TTLs, or by indicating that a domain name does not exist just because one of its name servers does not respond.
As a final level of complexity, some applications such as Web browsers also have their own DNS cache, in order to reduce the use of the DNS resolver library itself. This practice can add extra difficulty to DNS debugging, as it obscures which data is fresh, or lies in which cache. These caches typically have very short caching times of the order of one minute. A notable exception is Internet Explorer; recent versions cache DNS records for half an hour.[1]
Other applications
The system outlined above provides a somewhat simplified scenario. The Domain Name System includes several other functions:
Hostnames and IP addresses do not necessarily match on a one-to-one basis. Many hostnames may correspond to a single IP address: combined with virtual hosting, this allows a single machine to serve many web sites. Alternatively a single hostname may correspond to many IP addresses: this can facilitate fault tolerance and load distribution, and also allows a site to move physical location seamlessly.
There are many uses of DNS besides translating names to IP addresses. For instance, Mail transfer agents use DNS to find out where to deliver e-mail for a particular address. The domain to mail exchanger mapping provided by MX records accommodates another layer of fault tolerance and load distribution on top of the name to IP address mapping.
Sender Policy Framework and DomainKeys instead of creating their own record types were designed to take advantage of another DNS record type, the TXT record.
To provide resilience in the event of computer failure, multiple DNS servers are usually provided for coverage of each domain, and at the top level, thirteen very powerful root servers exist, with additional "copies" of several of them distributed worldwide via Anycast.
DNS primarily uses UDP on port 53 [2] to serve requests. Almost all DNS queries consist of a single UDP request from the client followed by a single UDP reply from the server. TCP comes into play only when the response data size exceeds 512 bytes, or for such tasks as zone transfer. Some operating systems such as HP-UX are known to have resolver implementations that use TCP for all queries, even when UDP would suffice.
Extensions to DNS
EDNS is an extension of the DNS protocol which enhances the transport of DNS data in UDP packages, and adds support for expanding the space of request and response codes. It is described in RFC 2671.
Standards
RFC 882 Concepts and Facilities (Deprecated by RFC 1034)
RFC 883 Domain Names: Implementation specification (Deprecated by RFC 1035)
RFC 920 Specified original TLDs: .arpa, .com, .edu, .org, .gov, .mil and two-character country codes
RFC 1032 Domain administrators guide
RFC 1033 Domain administrators operations guide
RFC 1034 Domain Names - Concepts and Facilities.
RFC 1035 Domain Names - Implementation and Specification
RFC 1101 DNS Encodings of Network Names and Other Types
RFC 1123 Requirements for Internet Hosts -- Application and Support
RFC 1183 New DNS RR Definitions
RFC 1706 DNS NSAP Resource Records
RFC 1876 Location Information in the DNS (LOC)
RFC 1886 DNS Extensions to support IP version 6
RFC 1912 Common DNS Operational and Configuration Errors
RFC 1995 Incremental Zone Transfer in DNS
RFC 1996 A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)
RFC 2136 Dynamic Updates in the domain name system (DNS UPDATE)
RFC 2181 Clarifications to the DNS Specification
RFC 2182 Selection and Operation of Secondary DNS Servers
RFC 2308 Negative Caching of DNS Queries (DNS NCACHE)
RFC 2317 Classless IN-ADDR.ARPA delegation
RFC 2671 Extension Mechanisms for DNS (EDNS0)
RFC 2672 Non-Terminal DNS Name Redirection (DNAME record)
RFC 2782 A DNS RR for specifying the location of services (DNS SRV)
RFC 2845 Secret Key Transaction Authentication for DNS (TSIG)
RFC 2874 DNS Extensions to Support IPv6 Address Aggregation and Renumbering
RFC 3403 Dynamic Delegation Discovery System (DDDS) (NAPTR records)
RFC 3696 Application Techniques for Checking and Transformation of Names
RFC 4398 Storing Certificates in the Domain Name System
RFC 4408 Sender Policy Framework (SPF) (SPF records)
Types of DNS records
Important categories of data stored in DNS include the following:
An A record or address record maps a hostname to a 32-bit IPv4 address.
An AAAA record or IPv6 address record maps a hostname to a 128-bit IPv6 address.
A CNAME record or canonical name record is an alias of one name to another. The A record to which the alias points can be either local or remote - on a foreign name server. This is useful when running multiple services (like an FTP and a webserver) from a single IP address. Each service can then have its own entry in DNS (like ftp.example.com. and www.example.com.)
An MX record or mail exchange record maps a domain name to a list of mail exchange servers for that domain.
A PTR record or pointer record maps an IPv4 address to the canonical name for that host. Setting up a PTR record for a hostname in the in-addr.arpa. domain that corresponds to an IP address implements reverse DNS lookup for that address. For example (at the time of writing), www.icann.net has the IP address 192.0.34.164, but a PTR record maps 164.34.0.192.in-addr.arpa to its canonical name, referrals.icann.org.
An NS record or name server record maps a domain name to a list of DNS servers authoritative for that domain. Delegations depend on NS records.
An SOA record or start of authority record specifies the DNS server providing authoritative information about an Internet domain, the email of the domain administrator, the domain serial number, and several timers relating to refreshing the zone.
An SRV record is a generalized service location record.
A TXT record allows an administrator to insert arbitrary text into a DNS record. For example, this record is used to implement the Sender Policy Framework and DomainKeys specifications.
NAPTR records ("Naming Authority Pointer") are a newer type of DNS record that support regular expression based rewriting.
Other types of records simply provide information (for example, a LOC record gives the physical location of a host), or experimental data (for example, a WKS record gives a list of servers offering some well known service such as HTTP or POP3 for a domain).
When sent over the internet, all records use the common format specified in RFC 1035 shown below.
RR (Resource Record) Fields
Field
Description
Length (Octets)
NAME
Name of the node to which this record pertains.
(variable)
TYPE
Type of RR. For example, MX is type 15.
2
CLASS
Class code.
2
TTL
Signed time in seconds that RR stays valid.
4
RDLENGTH
Length of RDATA field.
2
RDATA
Additional RR-specific data.
(variable)
For a complete list of DNS Record types consult IANA DNS Parameters.
Internationalized domain names
Main article: Internationalized domain name
While domain names technically have no restrictions on the characters they use and can include non-ASCII characters, the same is not true for host names.[3] Host names are the names most people see and use for things like e-mail and web browsing. Host names are restricted to a small subset of the ASCII character set that includes the Roman alphabet in upper and lower case, the digits 0 through 9, the dot, and the hyphen. (See RFC 3696 section 2 for details.) This prevented the representation of names and words of many languages natively. ICANN has approved the Punycode-based IDNA system, which maps Unicode strings into the valid DNS character set, as a workaround to this issue. Some registries have adopted IDNA.
Security issues
DNS was not originally designed with security in mind, and thus has a number of security issues. DNS responses are traditionally not cryptographically signed, leading to many attack possibilities; DNSSEC modifies DNS to add support for cryptographically signed responses. There are various extensions to support securing zone transfer information as well.
Even with encryption it still doesn't prevent the possibility that a DNS server could become infected with a virus (or for that matter a disgruntled employee) that would cause IP addresses of that server to be redirected to a malicious address with a long TTL. This could have far reaching impact to potentially millions of internet users if busy DNS servers cache the bad IP data. This would require manual purging of all affected DNS caches as required by the long TTL (up to 68 years).
Some domain names can spoof other, similar-looking domain names. For example, "paypal.com" and "paypa1.com" are different names, yet users may be unable to tell the difference when the user's typeface (font) does not clearly differentiate the letter l and the number 1. This problem is much more serious in systems that support internationalized domain names, since many characters that are different, from the point of view of ISO 10646, appear identical on typical computer screens.
Legal users of domains
Registrant
Most of the NICs in the world receive an annual fee from a legal user in order for the legal user to utilize the domain name (i.e. a sort of a leasing agreement exists, subject to the registry's terms and conditions). Depending on the various naming convention of the registries, legal users become commonly known as "registrants" or as "domain holders".
ICANN holds a complete list of domain registries in the world. One can find the legal user of a domain name by looking in the WHOIS database held by most domain registries.
For most of the more than 240 country code top-level domains (ccTLDs), the domain registries hold the authoritative WHOIS (Registrant, name servers, expiry dates etc.) For instance, DENIC, Germany NIC holds the authoritative WHOIS to a .DE domain name.
However, some domain registries, such as for .COM, .ORG, .INFO, etc., use a registry-registrar model. There are hundreds of Domain Name Registrars that actually perform the domain name registration with the end-user (see lists at ICANN or VeriSign). By using this method of distribution, the registry only has to manage the relationship with the registrar, and the registrar maintains the relationship with the end-users, or 'registrants'. For .COM, .NET domain names, the domain registries, VeriSign holds a basic WHOIS (registrar and name servers etc.) One can find the detailed WHOIS (registrant, name servers, expiry dates etc.) at the registrars.
Since about 2001, most gTLD registries (.ORG, .BIZ, .INFO) have adopted a so-called "thick" registry approach, i.e. keeping the authoritative WHOIS with the various registries instead of the registrars.
Administrative contact
A registrant usually designates an administrative contact to manage the domain name. In practice, the administrative contact usually has the most immediate power over a domain. Management functions delegated to the administrative contacts may include (for example):
the obligation to conform to the requirements of the domain registry in order to retain the right to use a domain name
authorization to update the physical address, e-mail address and telephone number etc. in WHOIS
Technical contact
A technical contact manages the name servers of a domain name. The many functions of a technical contact include:
making sure the configurations of the domain name conforms to the requirements of the domain registry
updating the domain zone
providing the 24×7 functionality of the name servers (that leads to the accessibility of the domain name)
Billing contact
The party whom a NIC invoices.
Name servers
Namely the authoritative name servers that host the domain name zone of a domain name.
Politics
Many investigators have voiced criticism of the methods currently used to control ownership of domains. Critics commonly claim abuse by monopolies or near-monopolies, such as VeriSign, Inc. Particularly noteworthy was the VeriSign Site Finder system which redirected all unregistered .com and .net domains to a VeriSign webpage. Despite widespread criticism, VeriSign only reluctantly removed it after the Internet Corporation for Assigned Names and Numbers (ICANN) threatened to revoke its contract to administer the root name servers.
There is also significant disquiet regarding 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 alternative DNS roots that would be beyond the control of any single country.
Truth in Domain Names Act
Main article: Anticybersquatting Consumer Protection Act
In the United States, the "Truth in Domain Names Act" (actually the "Anticybersquatting Consumer Protection Act"), in combination with the PROTECT Act, forbids the use of a misleading domain name with the intention of attracting people into viewing a visual depiction of sexually explicit conduct on the Internet.
See also
Dynamic DNS
Open Root Server Network
Comparison of DNS server software
The DNS resolver will almost invariably have a cache (see above) containing recent lookups. If the cache can provide the answer to the request, the resolver will return the value in the cache to the program that made the request. If the cache does not contain the answer, the resolver will send the request to a designated DNS server or servers. In the case of most home users, the Internet service provider to which the machine connects will usually supply this DNS server: such a user will either have configured that server's address manually or allowed DHCP to set it; however, where systems administrators have configured systems to use their own DNS servers, their DNS resolvers point to separately maintained nameservers of the organization. In any event, the name server thus queried will follow the process outlined above, until it either successfully finds a result or does not. It then returns its results to the DNS resolver; assuming it has found a result, the resolver duly caches that result for future use, and hands the result back to the software which initiated the request.
Broken resolvers
An additional level of complexity emerges when resolvers violate the rules of the DNS protocol. Some people have suggested[citation needed] that a number of large ISPs have configured their DNS servers to violate rules (presumably to allow them to run on less-expensive hardware than a fully compliant resolver), such as by disobeying TTLs, or by indicating that a domain name does not exist just because one of its name servers does not respond.
As a final level of complexity, some applications such as Web browsers also have their own DNS cache, in order to reduce the use of the DNS resolver library itself. This practice can add extra difficulty to DNS debugging, as it obscures which data is fresh, or lies in which cache. These caches typically have very short caching times of the order of one minute. A notable exception is Internet Explorer; recent versions cache DNS records for half an hour.[1]
Other applications
The system outlined above provides a somewhat simplified scenario. The Domain Name System includes several other functions:
Hostnames and IP addresses do not necessarily match on a one-to-one basis. Many hostnames may correspond to a single IP address: combined with virtual hosting, this allows a single machine to serve many web sites. Alternatively a single hostname may correspond to many IP addresses: this can facilitate fault tolerance and load distribution, and also allows a site to move physical location seamlessly.
There are many uses of DNS besides translating names to IP addresses. For instance, Mail transfer agents use DNS to find out where to deliver e-mail for a particular address. The domain to mail exchanger mapping provided by MX records accommodates another layer of fault tolerance and load distribution on top of the name to IP address mapping.
Sender Policy Framework and DomainKeys instead of creating their own record types were designed to take advantage of another DNS record type, the TXT record.
To provide resilience in the event of computer failure, multiple DNS servers are usually provided for coverage of each domain, and at the top level, thirteen very powerful root servers exist, with additional "copies" of several of them distributed worldwide via Anycast.
DNS primarily uses UDP on port 53 [2] to serve requests. Almost all DNS queries consist of a single UDP request from the client followed by a single UDP reply from the server. TCP comes into play only when the response data size exceeds 512 bytes, or for such tasks as zone transfer. Some operating systems such as HP-UX are known to have resolver implementations that use TCP for all queries, even when UDP would suffice.
Extensions to DNS
EDNS is an extension of the DNS protocol which enhances the transport of DNS data in UDP packages, and adds support for expanding the space of request and response codes. It is described in RFC 2671.
Standards
RFC 882 Concepts and Facilities (Deprecated by RFC 1034)
RFC 883 Domain Names: Implementation specification (Deprecated by RFC 1035)
RFC 920 Specified original TLDs: .arpa, .com, .edu, .org, .gov, .mil and two-character country codes
RFC 1032 Domain administrators guide
RFC 1033 Domain administrators operations guide
RFC 1034 Domain Names - Concepts and Facilities.
RFC 1035 Domain Names - Implementation and Specification
RFC 1101 DNS Encodings of Network Names and Other Types
RFC 1123 Requirements for Internet Hosts -- Application and Support
RFC 1183 New DNS RR Definitions
RFC 1706 DNS NSAP Resource Records
RFC 1876 Location Information in the DNS (LOC)
RFC 1886 DNS Extensions to support IP version 6
RFC 1912 Common DNS Operational and Configuration Errors
RFC 1995 Incremental Zone Transfer in DNS
RFC 1996 A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)
RFC 2136 Dynamic Updates in the domain name system (DNS UPDATE)
RFC 2181 Clarifications to the DNS Specification
RFC 2182 Selection and Operation of Secondary DNS Servers
RFC 2308 Negative Caching of DNS Queries (DNS NCACHE)
RFC 2317 Classless IN-ADDR.ARPA delegation
RFC 2671 Extension Mechanisms for DNS (EDNS0)
RFC 2672 Non-Terminal DNS Name Redirection (DNAME record)
RFC 2782 A DNS RR for specifying the location of services (DNS SRV)
RFC 2845 Secret Key Transaction Authentication for DNS (TSIG)
RFC 2874 DNS Extensions to Support IPv6 Address Aggregation and Renumbering
RFC 3403 Dynamic Delegation Discovery System (DDDS) (NAPTR records)
RFC 3696 Application Techniques for Checking and Transformation of Names
RFC 4398 Storing Certificates in the Domain Name System
RFC 4408 Sender Policy Framework (SPF) (SPF records)
Types of DNS records
Important categories of data stored in DNS include the following:
An A record or address record maps a hostname to a 32-bit IPv4 address.
An AAAA record or IPv6 address record maps a hostname to a 128-bit IPv6 address.
A CNAME record or canonical name record is an alias of one name to another. The A record to which the alias points can be either local or remote - on a foreign name server. This is useful when running multiple services (like an FTP and a webserver) from a single IP address. Each service can then have its own entry in DNS (like ftp.example.com. and www.example.com.)
An MX record or mail exchange record maps a domain name to a list of mail exchange servers for that domain.
A PTR record or pointer record maps an IPv4 address to the canonical name for that host. Setting up a PTR record for a hostname in the in-addr.arpa. domain that corresponds to an IP address implements reverse DNS lookup for that address. For example (at the time of writing), www.icann.net has the IP address 192.0.34.164, but a PTR record maps 164.34.0.192.in-addr.arpa to its canonical name, referrals.icann.org.
An NS record or name server record maps a domain name to a list of DNS servers authoritative for that domain. Delegations depend on NS records.
An SOA record or start of authority record specifies the DNS server providing authoritative information about an Internet domain, the email of the domain administrator, the domain serial number, and several timers relating to refreshing the zone.
An SRV record is a generalized service location record.
A TXT record allows an administrator to insert arbitrary text into a DNS record. For example, this record is used to implement the Sender Policy Framework and DomainKeys specifications.
NAPTR records ("Naming Authority Pointer") are a newer type of DNS record that support regular expression based rewriting.
Other types of records simply provide information (for example, a LOC record gives the physical location of a host), or experimental data (for example, a WKS record gives a list of servers offering some well known service such as HTTP or POP3 for a domain).
When sent over the internet, all records use the common format specified in RFC 1035 shown below.
RR (Resource Record) Fields
Field
Description
Length (Octets)
NAME
Name of the node to which this record pertains.
(variable)
TYPE
Type of RR. For example, MX is type 15.
2
CLASS
Class code.
2
TTL
Signed time in seconds that RR stays valid.
4
RDLENGTH
Length of RDATA field.
2
RDATA
Additional RR-specific data.
(variable)
For a complete list of DNS Record types consult IANA DNS Parameters.
Internationalized domain names
Main article: Internationalized domain name
While domain names technically have no restrictions on the characters they use and can include non-ASCII characters, the same is not true for host names.[3] Host names are the names most people see and use for things like e-mail and web browsing. Host names are restricted to a small subset of the ASCII character set that includes the Roman alphabet in upper and lower case, the digits 0 through 9, the dot, and the hyphen. (See RFC 3696 section 2 for details.) This prevented the representation of names and words of many languages natively. ICANN has approved the Punycode-based IDNA system, which maps Unicode strings into the valid DNS character set, as a workaround to this issue. Some registries have adopted IDNA.
Security issues
DNS was not originally designed with security in mind, and thus has a number of security issues. DNS responses are traditionally not cryptographically signed, leading to many attack possibilities; DNSSEC modifies DNS to add support for cryptographically signed responses. There are various extensions to support securing zone transfer information as well.
Even with encryption it still doesn't prevent the possibility that a DNS server could become infected with a virus (or for that matter a disgruntled employee) that would cause IP addresses of that server to be redirected to a malicious address with a long TTL. This could have far reaching impact to potentially millions of internet users if busy DNS servers cache the bad IP data. This would require manual purging of all affected DNS caches as required by the long TTL (up to 68 years).
Some domain names can spoof other, similar-looking domain names. For example, "paypal.com" and "paypa1.com" are different names, yet users may be unable to tell the difference when the user's typeface (font) does not clearly differentiate the letter l and the number 1. This problem is much more serious in systems that support internationalized domain names, since many characters that are different, from the point of view of ISO 10646, appear identical on typical computer screens.
Legal users of domains
Registrant
Most of the NICs in the world receive an annual fee from a legal user in order for the legal user to utilize the domain name (i.e. a sort of a leasing agreement exists, subject to the registry's terms and conditions). Depending on the various naming convention of the registries, legal users become commonly known as "registrants" or as "domain holders".
ICANN holds a complete list of domain registries in the world. One can find the legal user of a domain name by looking in the WHOIS database held by most domain registries.
For most of the more than 240 country code top-level domains (ccTLDs), the domain registries hold the authoritative WHOIS (Registrant, name servers, expiry dates etc.) For instance, DENIC, Germany NIC holds the authoritative WHOIS to a .DE domain name.
However, some domain registries, such as for .COM, .ORG, .INFO, etc., use a registry-registrar model. There are hundreds of Domain Name Registrars that actually perform the domain name registration with the end-user (see lists at ICANN or VeriSign). By using this method of distribution, the registry only has to manage the relationship with the registrar, and the registrar maintains the relationship with the end-users, or 'registrants'. For .COM, .NET domain names, the domain registries, VeriSign holds a basic WHOIS (registrar and name servers etc.) One can find the detailed WHOIS (registrant, name servers, expiry dates etc.) at the registrars.
Since about 2001, most gTLD registries (.ORG, .BIZ, .INFO) have adopted a so-called "thick" registry approach, i.e. keeping the authoritative WHOIS with the various registries instead of the registrars.
Administrative contact
A registrant usually designates an administrative contact to manage the domain name. In practice, the administrative contact usually has the most immediate power over a domain. Management functions delegated to the administrative contacts may include (for example):
the obligation to conform to the requirements of the domain registry in order to retain the right to use a domain name
authorization to update the physical address, e-mail address and telephone number etc. in WHOIS
Technical contact
A technical contact manages the name servers of a domain name. The many functions of a technical contact include:
making sure the configurations of the domain name conforms to the requirements of the domain registry
updating the domain zone
providing the 24×7 functionality of the name servers (that leads to the accessibility of the domain name)
Billing contact
The party whom a NIC invoices.
Name servers
Namely the authoritative name servers that host the domain name zone of a domain name.
Politics
Many investigators have voiced criticism of the methods currently used to control ownership of domains. Critics commonly claim abuse by monopolies or near-monopolies, such as VeriSign, Inc. Particularly noteworthy was the VeriSign Site Finder system which redirected all unregistered .com and .net domains to a VeriSign webpage. Despite widespread criticism, VeriSign only reluctantly removed it after the Internet Corporation for Assigned Names and Numbers (ICANN) threatened to revoke its contract to administer the root name servers.
There is also significant disquiet regarding 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 alternative DNS roots that would be beyond the control of any single country.
Truth in Domain Names Act
Main article: Anticybersquatting Consumer Protection Act
In the United States, the "Truth in Domain Names Act" (actually the "Anticybersquatting Consumer Protection Act"), in combination with the PROTECT Act, forbids the use of a misleading domain name with the intention of attracting people into viewing a visual depiction of sexually explicit conduct on the Internet.
See also
Dynamic DNS
Open Root Server Network
Comparison of DNS server software
Domain name
From Wikipedia, the free encyclopedia
The term domain name has multiple related meanings:
A name that identifies a computer or computers on the internet. These names appear as a component of a Web site's URL, e.g. wikipedia.org. This type of domain name is also called a hostname.
The product that domain name registrars provide to their customers. These names are often called registered domain names.
Names used for other purposes in the Domain Name System (DNS), for example the special name which follows the @ sign in an email address, or the Top-level domains like .com, or the names used by the Session Initiation Protocol (VoIP), or DomainKeys.
They are sometimes colloquially (and incorrectly) referred to by marketers as "web addresses".
This article will primarily discuss registered domain names. See the Domain Name System article for technical discussions about general domain names and the hostname article for further information about the most common type of domain name.
Overview
The most common types of domain names are hostnames that provide more memorable names to stand in for numeric IP addresses. They allow for any service to move to a different location in the topology of the Internet (or an intranet), which would then have a different IP address.
By allowing the use of unique alphabetical addresses instead of numeric ones, domain names allow Internet users to more easily find and communicate with web sites and other server-based services. The flexibility of the domain name system allows multiple IP addresses to be assigned to a single domain name, or multiple domain names to be assigned to a single IP address. This means that one server may have multiple roles (such as hosting multiple independent Web sites), or that one role can be spread among many servers. One IP address can also be assigned to several servers, as used in anycast and hijacked IP space.
Hostnames are restricted to the ASCII letters "a" through "z" (case-insensitive), the digits "0" through "9", and the hyphen, with some other restrictions. Registrars restrict the domains to valid hostnames, since, otherwise, they would be useless. The Internationalized domain name (IDN) system has been developed to bypass the restrictions on character allowances in hostnames, making it easier for users of non-english alphabets to use the Internet. The underscore character is frequently used to ensure that a domain name is not recognized as a hostname, for example with the use of SRV records, although some older systems, such as NetBIOS did allow it. Due to confusion and other reasons, domain names with underscores in them are sometimes used where hostnames are required.
Examples
The following example illustrates the difference between a URL (Uniform Resource Locator) and a domain name:
URL: http://www.example.net/index.html
Domain name: www.example.net
Registered domain name: example.net
As a general rule, the IP address and the server name are interchangeable. For most Internet services, the server will not have any way to know which was used. However, the explosion of interest in the Web means that there are far more Web sites than servers. To accommodate this, the hypertext transfer protocol (HTTP) specifies that the client tells the server which name is being used. This way, one server with one IP address can provide different sites for different domain names. This feature goes under the name virtual hosting and is commonly used by Web hosts.
For example, as referenced in RFC 2606 (Reserved Top Level DNS Names), the server at IP address 192.0.34.166 handles all of the following sites:
example.com
www.example.com
example.net
www.example.net
example.org
www.example.org
When a request is made, the data corresponding to the hostname requested is served to the user.
Top-level domains
Every domain name ends in a top-level domain (TLD) name, which is always either one of a small list of generic names (three or more characters), or a two-character territory code based on ISO-3166 (there are few exceptions and new codes are integrated case by case). Top-level domains are sometimes also called first-level domains.
The generic top-level domain (gTLD) extensions are:
[show] v • d • e Generic top-level domains
Unsponsored
.biz .com .edu .gov .info .int .mil .name .net .org
Sponsored
.aero .asia .cat .coop .jobs .mobi .museum .pro .tel .travel
Infrastructure
.arpa .root
Proposed
.berlin .bzh .cym .gal .geo .kid .kids .lat .mail .nyc .post .sco .web .xxx
Deleted/retired
.nato
Reserved
.example .invalid .localhost .test
Pseudo-domains
.bitnet .csnet .ip .local .onion .uucp
Unofficial
see Alternative DNS roots
See also: Country code top-level domains
The country code top-level domain (ccTLD) extensions are:
[show] v • d • e Country code top-level domains
Active: .ac .ad .ae .af .ag .ai .al .am .an .ao .aq .ar .as .at .au .aw .ax .az .ba .bb .bd .be .bf .bg .bh .bi .bj .bm .bn .bo .br .bs .bt .bw .by .bz .ca .cc .cd .cf .cg .ch .ci .ck .cl .cm .cn .co .cr .cu .cv .cx .cy .cz .de .dj .dk .dm .do .dz .ec .ee .eg .er .es .et .eu .fi .fj .fk .fm .fo .fr .ga .gd .ge .gf .gg .gh .gi .gl .gm .gn .gp .gq .gr .gs .gt .gu .gw .gy .hk .hm .hn .hr .ht .hu .id .ie .il .im .in .io .iq .ir .is .it .je .jm .jo .jp .ke .kg .kh .ki .km .kn .kr .kw .ky .kz .la .lb .lc .li .lk .lr .ls .lt .lu .lv .ly .ma .mc .md .mg .mh .mk .ml .mm .mn .mo .mp .mq .mr .ms .mt .mu .mv .mw .mx .my .mz .na .nc .ne .nf .ng .ni .nl .no .np .nr .nu .nz .om .pa .pe .pf .pg .ph .pk .pl .pn .pr .ps .pt .pw .py .qa .re .ro .ru .rw .sa .sb .sc .sd .se .sg .sh .si .sk .sl .sm .sn .sr .st .sv .sy .sz .tc .td .tf .tg .th .tj .tk .tl .tm .tn .to .tr .tt .tv .tw .tz .ua .ug .uk .us .uy .uz .va .vc .ve .vg .vi .vn .vu .wf .ws .ye .yu .za .zm .zw
Reserved/unassigned: .eh .kp .me .rs .um Allocated/unused: .bv .gb .pm .sj .so .yt Phaseout: .su .tp Deleted/retired: .bu .cs .dd .zr
See also: Generic top-level domains
Other-level domains
In addition to the top-level domains, there are 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 en.wikipedia.org, "wikipedia" is the second-level domain.
On the next level are third-level domains. These domains are immediately to the left of a second-level domain. In the en.wikipedia.org example, "en" is a third-level domain. There can be fourth and fifth level domains and so on, with virtually no limitation. An example of a working domain with five levels is www.sos.state.oh.us. Each level is separated by a dot or period symbol between them.
Domains of third or higher level are also known as subdomains, though this term technically applies to a domain of any level, since even a top-level domain is a "subdomain" of the "root" domain (a "zeroth-level" domain that is designated by a dot alone).
Traditionally, the second level domain was the name of the company or the name used on the internet. The third level was commonly 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. Modern technology now allows multiple servers to serve a single subdomain, or multiple protocols or domains to be served by a single computer. Therefore, subdomains may or may not have any real purpose.
Official assignment
ICANN (Internet Corporation for Assigned Names and Numbers) has overall responsibility for managing the DNS. It controls the root domain, delegating control over each top-level domain to a domain name registry. For ccTLDs, the domain registry is typically controlled by the government of that country. ICANN has a consultation role in these domain registries but is in no position to regulate the terms and conditions of how a domain name is allocated or who allocates it in each of these country level domain registries. On the other hand, generic top-level domains (gTLDs) are governed directly under ICANN which means all terms and conditions are defined by ICANN with the cooperation of the gTLD registries.
Domain names which are theoretically leased can be considered in the same way as real estate, due to a significant impact on online brand building, advertising, search engine optimization, etc.
A few companies have offered low-cost, below-cost or even free domain registrations, with a variety of models adopted to recoup the costs to the provider. These usually require that domains are hosted on their site in a framework or portal, with advertising wrapped around the user's content, revenue from which allows the provider to recoup the costs. When the DNS was new, domain registrations were free. A domain owner can generally give away or sell infinite subdomains of their domain, e.g. the owner of example.edu could provide domains that are subdomains, such as foo.example.edu and foo.bar.example.edu.
Uses and abuses
As domain names became attractive to marketers, rather than just the technical audience for which they were originally intended, they began to be used in manners that in many cases did not fit in their intended structure. As originally planned, the structure of domain names followed a strict hierarchy in which the top level domain indicated the type of organization (commercial, governmental, etc.), and addresses would be nested down to third, fourth, or further levels to express complex structures, where, for instance, branches, departments, and subsidiaries of a parent organization would have addresses which were subdomains of the parent domain. Also, hostnames were intended to correspond to actual physical machines on the network, generally with only one name per machine.
However, once the World Wide Web became popular, site operators frequently wished to have memorable addresses, regardless of whether they fit properly in the structure; thus, since the .com domain was the most popular and memorable, even noncommercial sites would often get addresses under it, and sites of all sorts wished to have second-level domain registrations even if they were parts of a larger entity where a logical subdomain would have made sense (e.g., abcnews.com instead of news.abc.com). A Web site found at http://www.example.org/ will often be advertised without the "http://", and in most cases can be reached by just entering "example.org" into a Web browser. In the case of a .com, the Web site can sometimes be reached by just entering "example" (depending on browser versions and configuration settings, which vary in how they interpret incomplete addresses).
The popularity of domain names also led to uses which were regarded as abusive by established companies with trademark rights; this was known as cybersquatting, in which somebody took a name that resembled a trademark in order to profit from traffic to that address. To combat this, various laws and policies were enacted to allow abusive registrations to be forcibly transferred, but these were sometimes themselves abused by overzealous companies committing reverse domain hijacking against domain users who had legitimate grounds to hold their names, such as their being generic words as well as trademarks in a particular context, or their use in the context of fan or protest sites with free speech rights of their own.
Laws that specifically address domain name conflicts include the Anticybersquatting Consumer Protection Act in the United States and the Trademarks Act, 1999, in India. Alternatively, domain registrants are bound by contract under the UDRP to comply with mandatory arbitration proceedings should someone challenge their ownership of the domain name.
Generic domain names — problems arising out of unregulated name selection
Within a particular top-level domain, parties are generally free to select an unallocated domain name as their own on a first come, first served basis, resulting in Harris's lament, all the good ones are taken. For generic or commonly used names, this may sometimes lead to the use of a domain name which is inaccurate or misleading. This problem can be seen with regard to the ownership or control of domain names for a generic product or service.
By way of illustration, there has been tremendous growth in the number and size of literary festivals around the world in recent years. In this context, currently a generic domain name such as literary.org is available to the first literary festival organisation which is able to obtain registration, even if the festival in question is very young or obscure. Some critics would argue that there is greater amenity in reserving such domain names for the use of, for example, a regional or umbrella grouping of festivals. Related issues may also arise in relation to non-commercial domain names.
Unconventional domain names
Due to the rarity of one-word dot-com domain names, many unconventional domain names, domain hacks, have been gaining popularity. They make use of the top-level domain as an integral part of the Web site's title. Two popular domain hack Web sites are del.icio.us and blo.gs, which spell out "delicious" and "blogs", respectively.
Unconventional domain names are also used to create unconventional email addresses. Non-working examples that spell 'James' are j@m.es and j@mes.com, which use the domain names m.es (of Spain's .es) and mes.com, respectively.
Commercial resale of domain names
An economic effect of the widespread usage of domain names has been the resale market (after-market) for generic domain names that has sprung up in the last decade. Certain domains, especially those related to business, gambling, pornography, and other commercially lucrative fields of digital world trade have become very much in demand to corporations and entrepreneurs due to their importance in attracting clients.
The most expensive Internet domain name to date, according to Guinness World Records, is business.com which was resold in 1999 for $7.5 million, but this was $7.5 million in stock options, not in cash. The stock was later redeemed for $2 million, "So it was $2 million."[1]. There are disputes about the high values of domain names claimed and the actual cash prices of many sales such Business.com. Another high-priced domain name, sex.com, was stolen from its rightful owner by means of a forged transfer instruction via fax. During the height of the dot-com era, the domain was earning millions of dollars per month in advertising revenue from the large influx of visitors that arrived daily. The sex.com sale may have never been final as the domain is still with the previous owner. Also, that sale was not just a domain but an income stream, a web site, a domain name with customers and advertisers, etc. Two long-running U.S. lawsuits resulted, one against the thief and one against the domain registrar VeriSign . In one of the cases, Kremen v. Network Solutions, the court found in favor of the plaintiff, leading to an unprecedented ruling that classified domain names as property, granting them the same legal protections. In 1999, Microsoft traded the name Bob.com with internet entrepreneur Bob Kerstein for the name Windows2000.com which was the name of their new operating system.
One of the reasons for the value of domain names is that even without advertising or marketing, they attract clients seeking services and products who simply type in the generic name. Furthermore, generic domain names such as movies.com or Books.com are extremely easy for potential customers to remember, increasing the probability that they become repeat customers or regular clients.
Although the current domain market is nowhere as strong as it was during the dot-com heyday, it remains strong and is currently experiencing solid growth again. Annually tens of millions of dollars change hands due to the resale of domains. Large numbers of registered domain names lapse and are deleted each year. On average 25,000 domain names drop (are deleted) every day.
It is very important to remember that a domain (name, address) must be valued separately from the website (content, revenue) that it is used for. The high prices have usually been paid for the revenue that was generated from the website at the domain's address (url.). The intrinsic value of a domain is the registration fee. There is no such a thing as a current market value for a domain: It just takes what somebody pays. The Fair Market Value of a domain can be anything from the registration fee: The lowest known past selling price, the highest known past selling, price, the most recent selling price, or just any past selling price and any of these (or any sum resp. division etc.) is usually added to the current or expected revenue from the web content (advertising, sales, etc.). Domain (name + ext.) should not be mixed with website (content + revenue). The estimation by appraisers are always the addition of what they would like that a domain is worth together with the effective/expected/desired revenue from the web content. Some people put value on the length of the SLD (name) and other people prefer description capability, but the shorter a SLD is, the less descriptive it can be. Also, if short is crucial, then the TLD (extension) should be short too. It is less realistic to get a domain like LL.travel or LL.mobi than a domain travel.LL or mobi.LL. This illustrates the relativity of domain value estimation. It can be safely put that the revenue af a web (content) can be easily stated, but that the value of a domain (SLD.TLD aka name.ext) is a matter of opinions and preferences. In the end, however, any sale depend of the estimates by the domain seller and the domain buyer.
People who buy and sell domain names are known as domainers. People who sell value estimation services are known as appraisers.
According to Guiness Book of World Records and MSNBC, the most expensive domain name sales on record as of 2004 were: Business.com for $7.5 million in December 1999, AsSeenOnTv.com for $5.1 million in January 2000, Altavista.com for $3.3 million in August 1998, Wine.com for $2.9 million in September 1999, CreditCards.com for $2.75 million in July 2004, and Autos.com for $2.2 million in December 1999.
Domain name confusion
Intercapping is often used to clarify a domain name. However, DNS is case-insensitive, and some names may be misinterpreted when converted to lowercase. For example: Who Represents, a database of artists and agents, chose whorepresents.com; a therapists' network thought therapistfinder.com looked good; and another website operating as of October 2006, is penisland.net a website for Pen Island, a site that claims to be an online pen vendor, but exists primarily as a joke, as it has no products for sale. Other examples include cummingfirst.com, website of the Cumming First United Church in Cumming, GA and powergenitalia.com, a website for an Italian Power Generator company. In such situations, the proper wording can be clarified by use of hyphens. For instance, Experts Exchange, the programmers' site, for a long time used expertsexchange.com, but ultimately changed the name to experts-exchange.com.
Leo Stoller threatened to sue the owners of StealThisEmail.com on the basis that, when read as stealthisemail.com, it infringed on claimed trademark rights to the word "stealth".
References
^ [Steven] (2006-10-16). Sticking to The Business (HTML). Newsweek. The Washington Post Company. Retrieved on 2007-07-14.
See also
Domaining
Domain hack
Domain hijacking
Domain tasting, also known as domain kiting
Domain name warehousing
Fully qualified domain name
ICANN
Internationalized domain name
Name generator
Uniform Resource Locator
World Wide Web
Web page
Web site
Geodomain
The term domain name has multiple related meanings:
A name that identifies a computer or computers on the internet. These names appear as a component of a Web site's URL, e.g. wikipedia.org. This type of domain name is also called a hostname.
The product that domain name registrars provide to their customers. These names are often called registered domain names.
Names used for other purposes in the Domain Name System (DNS), for example the special name which follows the @ sign in an email address, or the Top-level domains like .com, or the names used by the Session Initiation Protocol (VoIP), or DomainKeys.
They are sometimes colloquially (and incorrectly) referred to by marketers as "web addresses".
This article will primarily discuss registered domain names. See the Domain Name System article for technical discussions about general domain names and the hostname article for further information about the most common type of domain name.
Overview
The most common types of domain names are hostnames that provide more memorable names to stand in for numeric IP addresses. They allow for any service to move to a different location in the topology of the Internet (or an intranet), which would then have a different IP address.
By allowing the use of unique alphabetical addresses instead of numeric ones, domain names allow Internet users to more easily find and communicate with web sites and other server-based services. The flexibility of the domain name system allows multiple IP addresses to be assigned to a single domain name, or multiple domain names to be assigned to a single IP address. This means that one server may have multiple roles (such as hosting multiple independent Web sites), or that one role can be spread among many servers. One IP address can also be assigned to several servers, as used in anycast and hijacked IP space.
Hostnames are restricted to the ASCII letters "a" through "z" (case-insensitive), the digits "0" through "9", and the hyphen, with some other restrictions. Registrars restrict the domains to valid hostnames, since, otherwise, they would be useless. The Internationalized domain name (IDN) system has been developed to bypass the restrictions on character allowances in hostnames, making it easier for users of non-english alphabets to use the Internet. The underscore character is frequently used to ensure that a domain name is not recognized as a hostname, for example with the use of SRV records, although some older systems, such as NetBIOS did allow it. Due to confusion and other reasons, domain names with underscores in them are sometimes used where hostnames are required.
Examples
The following example illustrates the difference between a URL (Uniform Resource Locator) and a domain name:
URL: http://www.example.net/index.html
Domain name: www.example.net
Registered domain name: example.net
As a general rule, the IP address and the server name are interchangeable. For most Internet services, the server will not have any way to know which was used. However, the explosion of interest in the Web means that there are far more Web sites than servers. To accommodate this, the hypertext transfer protocol (HTTP) specifies that the client tells the server which name is being used. This way, one server with one IP address can provide different sites for different domain names. This feature goes under the name virtual hosting and is commonly used by Web hosts.
For example, as referenced in RFC 2606 (Reserved Top Level DNS Names), the server at IP address 192.0.34.166 handles all of the following sites:
example.com
www.example.com
example.net
www.example.net
example.org
www.example.org
When a request is made, the data corresponding to the hostname requested is served to the user.
Top-level domains
Every domain name ends in a top-level domain (TLD) name, which is always either one of a small list of generic names (three or more characters), or a two-character territory code based on ISO-3166 (there are few exceptions and new codes are integrated case by case). Top-level domains are sometimes also called first-level domains.
The generic top-level domain (gTLD) extensions are:
[show] v • d • e Generic top-level domains
Unsponsored
.biz .com .edu .gov .info .int .mil .name .net .org
Sponsored
.aero .asia .cat .coop .jobs .mobi .museum .pro .tel .travel
Infrastructure
.arpa .root
Proposed
.berlin .bzh .cym .gal .geo .kid .kids .lat .mail .nyc .post .sco .web .xxx
Deleted/retired
.nato
Reserved
.example .invalid .localhost .test
Pseudo-domains
.bitnet .csnet .ip .local .onion .uucp
Unofficial
see Alternative DNS roots
See also: Country code top-level domains
The country code top-level domain (ccTLD) extensions are:
[show] v • d • e Country code top-level domains
Active: .ac .ad .ae .af .ag .ai .al .am .an .ao .aq .ar .as .at .au .aw .ax .az .ba .bb .bd .be .bf .bg .bh .bi .bj .bm .bn .bo .br .bs .bt .bw .by .bz .ca .cc .cd .cf .cg .ch .ci .ck .cl .cm .cn .co .cr .cu .cv .cx .cy .cz .de .dj .dk .dm .do .dz .ec .ee .eg .er .es .et .eu .fi .fj .fk .fm .fo .fr .ga .gd .ge .gf .gg .gh .gi .gl .gm .gn .gp .gq .gr .gs .gt .gu .gw .gy .hk .hm .hn .hr .ht .hu .id .ie .il .im .in .io .iq .ir .is .it .je .jm .jo .jp .ke .kg .kh .ki .km .kn .kr .kw .ky .kz .la .lb .lc .li .lk .lr .ls .lt .lu .lv .ly .ma .mc .md .mg .mh .mk .ml .mm .mn .mo .mp .mq .mr .ms .mt .mu .mv .mw .mx .my .mz .na .nc .ne .nf .ng .ni .nl .no .np .nr .nu .nz .om .pa .pe .pf .pg .ph .pk .pl .pn .pr .ps .pt .pw .py .qa .re .ro .ru .rw .sa .sb .sc .sd .se .sg .sh .si .sk .sl .sm .sn .sr .st .sv .sy .sz .tc .td .tf .tg .th .tj .tk .tl .tm .tn .to .tr .tt .tv .tw .tz .ua .ug .uk .us .uy .uz .va .vc .ve .vg .vi .vn .vu .wf .ws .ye .yu .za .zm .zw
Reserved/unassigned: .eh .kp .me .rs .um Allocated/unused: .bv .gb .pm .sj .so .yt Phaseout: .su .tp Deleted/retired: .bu .cs .dd .zr
See also: Generic top-level domains
Other-level domains
In addition to the top-level domains, there are 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 en.wikipedia.org, "wikipedia" is the second-level domain.
On the next level are third-level domains. These domains are immediately to the left of a second-level domain. In the en.wikipedia.org example, "en" is a third-level domain. There can be fourth and fifth level domains and so on, with virtually no limitation. An example of a working domain with five levels is www.sos.state.oh.us. Each level is separated by a dot or period symbol between them.
Domains of third or higher level are also known as subdomains, though this term technically applies to a domain of any level, since even a top-level domain is a "subdomain" of the "root" domain (a "zeroth-level" domain that is designated by a dot alone).
Traditionally, the second level domain was the name of the company or the name used on the internet. The third level was commonly 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. Modern technology now allows multiple servers to serve a single subdomain, or multiple protocols or domains to be served by a single computer. Therefore, subdomains may or may not have any real purpose.
Official assignment
ICANN (Internet Corporation for Assigned Names and Numbers) has overall responsibility for managing the DNS. It controls the root domain, delegating control over each top-level domain to a domain name registry. For ccTLDs, the domain registry is typically controlled by the government of that country. ICANN has a consultation role in these domain registries but is in no position to regulate the terms and conditions of how a domain name is allocated or who allocates it in each of these country level domain registries. On the other hand, generic top-level domains (gTLDs) are governed directly under ICANN which means all terms and conditions are defined by ICANN with the cooperation of the gTLD registries.
Domain names which are theoretically leased can be considered in the same way as real estate, due to a significant impact on online brand building, advertising, search engine optimization, etc.
A few companies have offered low-cost, below-cost or even free domain registrations, with a variety of models adopted to recoup the costs to the provider. These usually require that domains are hosted on their site in a framework or portal, with advertising wrapped around the user's content, revenue from which allows the provider to recoup the costs. When the DNS was new, domain registrations were free. A domain owner can generally give away or sell infinite subdomains of their domain, e.g. the owner of example.edu could provide domains that are subdomains, such as foo.example.edu and foo.bar.example.edu.
Uses and abuses
As domain names became attractive to marketers, rather than just the technical audience for which they were originally intended, they began to be used in manners that in many cases did not fit in their intended structure. As originally planned, the structure of domain names followed a strict hierarchy in which the top level domain indicated the type of organization (commercial, governmental, etc.), and addresses would be nested down to third, fourth, or further levels to express complex structures, where, for instance, branches, departments, and subsidiaries of a parent organization would have addresses which were subdomains of the parent domain. Also, hostnames were intended to correspond to actual physical machines on the network, generally with only one name per machine.
However, once the World Wide Web became popular, site operators frequently wished to have memorable addresses, regardless of whether they fit properly in the structure; thus, since the .com domain was the most popular and memorable, even noncommercial sites would often get addresses under it, and sites of all sorts wished to have second-level domain registrations even if they were parts of a larger entity where a logical subdomain would have made sense (e.g., abcnews.com instead of news.abc.com). A Web site found at http://www.example.org/ will often be advertised without the "http://", and in most cases can be reached by just entering "example.org" into a Web browser. In the case of a .com, the Web site can sometimes be reached by just entering "example" (depending on browser versions and configuration settings, which vary in how they interpret incomplete addresses).
The popularity of domain names also led to uses which were regarded as abusive by established companies with trademark rights; this was known as cybersquatting, in which somebody took a name that resembled a trademark in order to profit from traffic to that address. To combat this, various laws and policies were enacted to allow abusive registrations to be forcibly transferred, but these were sometimes themselves abused by overzealous companies committing reverse domain hijacking against domain users who had legitimate grounds to hold their names, such as their being generic words as well as trademarks in a particular context, or their use in the context of fan or protest sites with free speech rights of their own.
Laws that specifically address domain name conflicts include the Anticybersquatting Consumer Protection Act in the United States and the Trademarks Act, 1999, in India. Alternatively, domain registrants are bound by contract under the UDRP to comply with mandatory arbitration proceedings should someone challenge their ownership of the domain name.
Generic domain names — problems arising out of unregulated name selection
Within a particular top-level domain, parties are generally free to select an unallocated domain name as their own on a first come, first served basis, resulting in Harris's lament, all the good ones are taken. For generic or commonly used names, this may sometimes lead to the use of a domain name which is inaccurate or misleading. This problem can be seen with regard to the ownership or control of domain names for a generic product or service.
By way of illustration, there has been tremendous growth in the number and size of literary festivals around the world in recent years. In this context, currently a generic domain name such as literary.org is available to the first literary festival organisation which is able to obtain registration, even if the festival in question is very young or obscure. Some critics would argue that there is greater amenity in reserving such domain names for the use of, for example, a regional or umbrella grouping of festivals. Related issues may also arise in relation to non-commercial domain names.
Unconventional domain names
Due to the rarity of one-word dot-com domain names, many unconventional domain names, domain hacks, have been gaining popularity. They make use of the top-level domain as an integral part of the Web site's title. Two popular domain hack Web sites are del.icio.us and blo.gs, which spell out "delicious" and "blogs", respectively.
Unconventional domain names are also used to create unconventional email addresses. Non-working examples that spell 'James' are j@m.es and j@mes.com, which use the domain names m.es (of Spain's .es) and mes.com, respectively.
Commercial resale of domain names
An economic effect of the widespread usage of domain names has been the resale market (after-market) for generic domain names that has sprung up in the last decade. Certain domains, especially those related to business, gambling, pornography, and other commercially lucrative fields of digital world trade have become very much in demand to corporations and entrepreneurs due to their importance in attracting clients.
The most expensive Internet domain name to date, according to Guinness World Records, is business.com which was resold in 1999 for $7.5 million, but this was $7.5 million in stock options, not in cash. The stock was later redeemed for $2 million, "So it was $2 million."[1]. There are disputes about the high values of domain names claimed and the actual cash prices of many sales such Business.com. Another high-priced domain name, sex.com, was stolen from its rightful owner by means of a forged transfer instruction via fax. During the height of the dot-com era, the domain was earning millions of dollars per month in advertising revenue from the large influx of visitors that arrived daily. The sex.com sale may have never been final as the domain is still with the previous owner. Also, that sale was not just a domain but an income stream, a web site, a domain name with customers and advertisers, etc. Two long-running U.S. lawsuits resulted, one against the thief and one against the domain registrar VeriSign . In one of the cases, Kremen v. Network Solutions, the court found in favor of the plaintiff, leading to an unprecedented ruling that classified domain names as property, granting them the same legal protections. In 1999, Microsoft traded the name Bob.com with internet entrepreneur Bob Kerstein for the name Windows2000.com which was the name of their new operating system.
One of the reasons for the value of domain names is that even without advertising or marketing, they attract clients seeking services and products who simply type in the generic name. Furthermore, generic domain names such as movies.com or Books.com are extremely easy for potential customers to remember, increasing the probability that they become repeat customers or regular clients.
Although the current domain market is nowhere as strong as it was during the dot-com heyday, it remains strong and is currently experiencing solid growth again. Annually tens of millions of dollars change hands due to the resale of domains. Large numbers of registered domain names lapse and are deleted each year. On average 25,000 domain names drop (are deleted) every day.
It is very important to remember that a domain (name, address) must be valued separately from the website (content, revenue) that it is used for. The high prices have usually been paid for the revenue that was generated from the website at the domain's address (url.). The intrinsic value of a domain is the registration fee. There is no such a thing as a current market value for a domain: It just takes what somebody pays. The Fair Market Value of a domain can be anything from the registration fee: The lowest known past selling price, the highest known past selling, price, the most recent selling price, or just any past selling price and any of these (or any sum resp. division etc.) is usually added to the current or expected revenue from the web content (advertising, sales, etc.). Domain (name + ext.) should not be mixed with website (content + revenue). The estimation by appraisers are always the addition of what they would like that a domain is worth together with the effective/expected/desired revenue from the web content. Some people put value on the length of the SLD (name) and other people prefer description capability, but the shorter a SLD is, the less descriptive it can be. Also, if short is crucial, then the TLD (extension) should be short too. It is less realistic to get a domain like LL.travel or LL.mobi than a domain travel.LL or mobi.LL. This illustrates the relativity of domain value estimation. It can be safely put that the revenue af a web (content) can be easily stated, but that the value of a domain (SLD.TLD aka name.ext) is a matter of opinions and preferences. In the end, however, any sale depend of the estimates by the domain seller and the domain buyer.
People who buy and sell domain names are known as domainers. People who sell value estimation services are known as appraisers.
According to Guiness Book of World Records and MSNBC, the most expensive domain name sales on record as of 2004 were: Business.com for $7.5 million in December 1999, AsSeenOnTv.com for $5.1 million in January 2000, Altavista.com for $3.3 million in August 1998, Wine.com for $2.9 million in September 1999, CreditCards.com for $2.75 million in July 2004, and Autos.com for $2.2 million in December 1999.
Domain name confusion
Intercapping is often used to clarify a domain name. However, DNS is case-insensitive, and some names may be misinterpreted when converted to lowercase. For example: Who Represents, a database of artists and agents, chose whorepresents.com; a therapists' network thought therapistfinder.com looked good; and another website operating as of October 2006, is penisland.net a website for Pen Island, a site that claims to be an online pen vendor, but exists primarily as a joke, as it has no products for sale. Other examples include cummingfirst.com, website of the Cumming First United Church in Cumming, GA and powergenitalia.com, a website for an Italian Power Generator company. In such situations, the proper wording can be clarified by use of hyphens. For instance, Experts Exchange, the programmers' site, for a long time used expertsexchange.com, but ultimately changed the name to experts-exchange.com.
Leo Stoller threatened to sue the owners of StealThisEmail.com on the basis that, when read as stealthisemail.com, it infringed on claimed trademark rights to the word "stealth".
References
^ [Steven] (2006-10-16). Sticking to The Business (HTML). Newsweek. The Washington Post Company. Retrieved on 2007-07-14.
See also
Domaining
Domain hack
Domain hijacking
Domain tasting, also known as domain kiting
Domain name warehousing
Fully qualified domain name
ICANN
Internationalized domain name
Name generator
Uniform Resource Locator
World Wide Web
Web page
Web site
Geodomain
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