Domain Name Systems
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. www.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.
References
- ^ How Internet Explorer uses the cache for DNS host entries. Microsoft (2004).
- ^ Mockapetris, P (November, 1987). RFC1035: Domain Names - Implementation and Specification.
- ^ The term host name is here being used to mean an FQDN for a host, such as eg. en.wikipedia.org., and not just (to use the same example) en .
While most domain names do indeed designate hosts, some domain name DNS entries may not. In this sense, a (FQDN) hostname is a type of domain name, but not all domain names are actual host names. Cf. this host name vs domain name explanation from the DNS OP IETF Working Group.
Links
- dmoz.org overview of web-based DNS tools
- DNS Complexity, Paul Vixie, ACM Queue
- Open Source Guide - DNS for Rocket Scientists, an on-line technical book for further reading
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
How DNS works in theory
Domain names, arranged in a tree, cut into zones, each served by a nameserver.
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.
A DNS recursor consults three nameservers to resolve the address www.wikipedia.org.
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.
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.
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
How DNS works 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 (i.e. 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 (i.e. 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 resolving from program to OS-resolver to ISP-resolver to greater system.
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 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.
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.
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
DNS 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.
| 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.
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
Internationalized domain names and security
Internationalized domain names
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. 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.
Domain name regulation
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 the United States' political influence over ICANN. This was a significant issue in the attempt to create a .xxx top-level domain and sparked greater interest in alternative DNS roots that would be beyond the control of any single country.
Truth in Domain Names 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.
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
Domain names
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".
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:
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
The country code top-level domain (ccTLD) extensions are:
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
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.
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". [5].
References
- ^ [Steven] (2006-10-16). Sticking to The Business (HTML). Newsweek. The Washington Post Company.
Links
- RFC 1034, Domain Names—Concepts and Facilities, an Internet Protocol Standard.
- ICANN - Internet Corporation for Assigned Names and Numbers.
- UDRP, Uniform Domain-Name Dispute-Resolution Policy.
- Internic.net, public information regarding Internet domain name registration services.
- IANA generic TLD
- IANA Two letter Country Code TLD
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
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 [1]. 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. [2]
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. [3] 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. [4]
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
Country code top-level domains
A country code top-level domain (ccTLD) is an Internet top-level domain generally used or reserved for a country or a dependent territory.
ccTLD identifiers are two letters long, and all two-letter top-level domains are ccTLDs. Creation and delegation of ccTLDs is performed by the Internet Assigned Numbers Authority (IANA), and with certain exceptions noted below corresponds to the ISO 3166-1 alpha-2 country codes maintained by the United Nations.
Delegation and management
The IANA (currently contracted to ICANN) is responsible for determining an appropriate trustee for each ccTLD. Administration and control is then delegated to that entity, which is responsible for the policies and operation of the domain; the current delegation can be determined from IANA's list of ccTLDs. Individual ccTLDs may thus have varying requirements and fees for registering subdomains. There may be a local presence requirement (for instance, citizenship or other connection to the ccTLD), as for example the Canadian (ca) and German (de) domains, or registration may be open.
Links
- IANA's list of ccTLDs – official site
- World Intellectual Property Organization (WIPO) Domain name dispute resolution
- World-Wide Alliance of Top Level Domain-names
- Norid: Domain name registries around the world
- ccTLD study 2005
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
ISO 3166-1 and ccTLDs
ISO 3166-1 codes not used as ccTLDs
The codes EH and KP, although theoretically available as ccTLDs for Western Sahara and North Korea, have never been assigned and do not exist in DNS. Similarly, the code CS (Serbia and Montenegro) is not assigned an operator (cs was previously assigned to Czechoslovakia). TL (post-independence East Timor), is now being introduced to replace TP.
All other current ISO 3166-1 codes have been assigned and do exist in DNS. However, some of these are effectively unused. In particular, the ccTLDs for the Norwegian dependency Bouvet Island (bv) and the designation Svalbard and Jan Mayen (sj) do exist in DNS, but no subdomains have been assigned, and it is Norid policy not to assign any at present. Only one subdomain is still registered in gb (ISO 3166-1 for United Kingdom) and no new registrations are being accepted for it. Sites in the UK generally use uk (see below).
ccTLDs not in ISO 3166-1
Six ccTLDs are currently in use despite not being ISO 3166-1 two-letter codes. Some of these codes were in older ISO 3166-1 two-letter codes (now listed in ISO 3166-3).
- uk (United Kingdom): The ISO 3166-1 code for the United Kingdom is GB, however the JANET network had already selected uk as a top-level identifier for its pre-existing Name Registration Scheme, and this was incorporated into the top-level domains. gb was assigned with the intention of a transition, but this never occurred and the use of uk is now entrenched.
- su (the obsolete ISO 3166-1 code for Soviet Union): The su managers stated in 2001 they will commence accepting new su registrations, but it is unclear whether this action is compatible with ICANN policy.
- ac (Ascension Island): This code is a vestige of IANA's decision in 1996 to allow the use of codes reserved in the ISO 3166-1 alpha-2 reserve list for use by the Universal Postal Union. The decision was later reversed, with Ascension Island now the sole outlier. (Three other ccTLDs, gg (Guernsey), im (Isle of Man) and je (Jersey) also fell under this category from 1996 until they received corresponding ISO 3166 codes in March 2006.)
- eu (European Union): On September 25, 2000, ICANN decided to allow the use of any two-letter code in the ISO 3166-1 reserve list that is reserved for all purposes. Only EU currently meets this criterion. Following a decision by the EU's Council of Telecommunications Ministers in March 2002, progress was slow, but a registry (named EURid) was chosen by the European Commission, and criteria for allocation set: ICANN approved eu as a ccTLD, and it opened for registration on 7 December 2005 for the holders of prior rights. Since 7 April 2006, registration is open to all.
- tp (the previous ISO 3166-1 code for East Timor): To be phased out in favour of tl during 2005.
- yu (the previous ISO 3166-1 code for Serbia and Montenegro, when it was still known as Yugoslavia)
Historical ccTLDs
There are two ccTLDs which have been deleted after the corresponding 2-letter code was withdrawn from ISO 3166-1, namely cs (for Czechoslovakia) and zr (for Zaire). There had also been a ccTLD for the GDR, dd, which was never used at all. There may be a significant delay between withdrawal from ISO 3166-1 and deletion from the DNS; for example, ZR ceased to be an ISO 3166-1 code in 1997, but the zr ccTLD was not deleted until 2001. Other ccTLDs corresponding to obsolete ISO 3166-1 have not yet been deleted; in some cases they may never be deleted due to the amount of disruption this would cause for a heavily used ccTLD. In particular, the Soviet Union's ccTLD su remains in use more than a decade after SU was removed from ISO 3166-1.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
Unconventional and Vanity ccTLD usage
Unconventional ccTLD usage
Lenient registration restrictions on certain ccTLDs have resulted in domain names like I.am, tip.it, start.at and go.to. Other variations of ccTLD usage have been called domain hacks, where the Second-level domain and ccTLD are used together to form one word or one title. This has resulted in domains like blo.gs of South Georgia and the South Sandwich Islands (gs), del.icio.us of United States of America (us), and cr.yp.to of Tonga (to). (Non country code TLDs have also been used, like inter.net which uses the .net gTLD, probably the first domain hack ever.)
Vanity ccTLDs
Vanity ccTLDs are TLDs which are used largely for business purposes, usually outside their home countries, because of their name. For example,
- ad is a ccTLD for Andorra, but has recently been increasingly used by advertising agencies.
- ag is a ccTLD for Antigua and Barbuda and is sometimes used for agricultural sites.
- am is a ccTLD for Armenia, but is often used for AM radio stations.
- cc is a ccTLD for Cocos (Keeling) Islands but is used for a wide variety of sites.
- cd is a ccTLD for Democratic Republic of Congo but is used for CD merchants and file sharing sites.
- fm is a ccTLD for the Federated States of Micronesia but it is often used for FM radio stations.
- gg is a ccTLD for Guernsey but it is often used by the gaming and gambling industry, particularly in relation to horse racing gee-gee.
- in is a ccTLD for India but is widely used in the internet industry.
- je is a ccTLD for Jersey but is often used as a diminutive in Dutch (e.g. "huis.je"), as "you" ("zoek.je" = "search ye!"), or as "I" in French (e.g. "moi.je")
- la is a ccTLD for Laos but is marketed as the TLD for Los Angeles.
- nu is a ccTLD for Niue but marketed as resembling "new" in English and "now" in Nordic/Dutch. Also meaning "nude" in French.
- sc is a ccTLD for Seychelles but is often used as .Source
- tv is a ccTLD for Tuvalu but it is used for the tv/entertainment industry purposes.
- ws is a ccTLD for Samoa (earlier Western Samoa) is marketed as .Website
- vu is a ccTLD for Vanuatu but means "seen" in French.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
List of ccTLDs
*=Foreign registration permitted
A
.ac – Ascension Island *
.ad – Andorra
.ae – United Arab Emirates
.af – Afghanistan
.ag – Antigua and Barbuda *
.ai – Anguilla
.al – Albania
.am – Armenia *
.an – Netherlands Antilles
.ao – Angola
.aq – Antarctica
.ar – Argentina
.as – American Samoa *
.at – Austria *
.au – Australia
.aw – Aruba
.ax – Aland Islands
.az – Azerbaijan
B
.ba – Bosnia and Herzegovina
.bb – Barbados
.bd – Bangladesh
.be – Belgium *
.bf – Burkina Faso
.bg – Bulgaria
.bh – Bahrain
.bi – Burundi *
.bj – Benin
.bm – Bermuda
.bn – Brunei
.bo – Bolivia *
.br – Brazil *
.bs – Bahamas *
.bt – Bhutan
.bv – Bouvet Island (not in use; no registrations)
.bw – Botswana
.by – Belarus
.bz – Belize *
C
.ca – Canada
.cc – Cocos (Keeling) Islands *
.cd – Democratic Republic of the Congo (formerly .zr – Zaire) *
.cf – Central African Republic
.cg – Republic of the Congo *
.ch – Switzerland *
.ci – Côte d'Ivoire (Ivory Coast)
.ck – Cook Islands *
.cl – Chile
.cm – Cameroon
.cn – People's Republic of China *
.co – Colombia
.cr – Costa Rica
.cs – Serbia and Montenegro (formerly .yu – Yugoslavia; Note: on June 3, 2006, Montenegro declared independence, thus dissolving the state union) (.cs code not assigned; no DNS) (.cs code previously used for Czechoslovakia)
.cu – Cuba
.cv – Cape Verde
.cx – Christmas Island *
.cy – Cyprus
.cz – Czech Republic
D
.de – Germany
.dj – Djibouti *
.dk – Denmark *
.dm – Dominica
.do – Dominican Republic
.dz – Algeria
E
.ec – Ecuador
.ee – Estonia
.eg – Egypt
.eh – Western Sahara (not assigned; no DNS)
.er – Eritrea
.es – Spain *
.et – Ethiopia
.eu – European Union (code "exceptionally reserved" by ISO 3166-1)
F
.fi – Finland
.fj – Fiji *
.fk – Falkland Islands
.fm – Federated States of Micronesia *
.fo – Faroe Islands
.fr – France
G
.ga – Gabon
.gb – United Kingdom (Reserved domain by IANA; deprecated – see .uk)
.gd – Grenada
.ge – Georgia
.gf – French Guiana
.gg – Guernsey
.gh – Ghana
.gi – Gibraltar
.gl – Greenland *
.gm – Gambia
.gn – Guinea
.gp – Guadeloupe
.gq – Equatorial Guinea
.gr – Greece *
.gs – South Georgia and the South Sandwich Islands *
.gt – Guatemala
.gu – Guam
.gw – Guinea-Bissau
.gy – Guyana
H
.hk – Hong Kong *
.hm – Heard Island and McDonald Islands *
.hn – Honduras *
.hr – Croatia
.ht – Haiti
.hu – Hungary *
I
.id – Indonesia
.ie – Ireland
.il – Israel *
.im – Isle of Man *
.in – India *
.io – British Indian Ocean Territory *
.iq – Iraq
.ir – Iran *
.is – Iceland
.it – Italy
J
.je – Jersey
.jm – Jamaica
.jo – Jordan
.jp – Japan
K
.ke – Kenya
.kg – Kyrgyzstan
.kh – Cambodia
.ki – Kiribati
.km – Comoros
.kn – Saint Kitts and Nevis
.kp – North Korea (not assigned; no DNS)
.kr – South Korea
.kw – Kuwait
.ky – Cayman Islands
.kz – Kazakhstan *
L
.la – Laos *
.lb – Lebanon
.lc – Saint Lucia
.li – Liechtenstein *
.lk – Sri Lanka
.lr – Liberia
.ls – Lesotho
.lt – Lithuania
.lu – Luxembourg
.lv – Latvia *
.ly – Libya *
M
.ma – Morocco
.mc – Monaco
.md – Moldova *
.me – Montenegro
.mg – Madagascar
.mh – Marshall Islands
.mk – Republic of Macedonia
.ml – Mali
.mm – Myanmar
.mn – Mongolia *
.mo – Macau
.mp – Northern Mariana Islands *
.mq – Martinique
.mr – Mauritania
.ms – Montserrat *
.mt – Malta
.mu – Mauritius *
.mv – Maldives
.mw – Malawi *
.mx – Mexico *
.my – Malaysia
.mz – Mozambique
N
.na – Namibia *
.nc – New Caledonia
.ne – Niger
.nf – Norfolk Island *
.ng – Nigeria
.ni – Nicaragua
.nl – Netherlands * (first ccTLD registered)
.no – Norway
.np – Nepal
.nr – Nauru *
.nu – Niue *
.nz – New Zealand *
O
.om – Oman
P
.pa – Panama
.pe – Peru
.pf – French Polynesia
.pg – Papua New Guinea
.ph – Philippines *
.pk – Pakistan *
.pl – Poland *
.pm – Saint Pierre and Miquelon
.pn – Pitcairn Islands *
.pr – Puerto Rico *
.ps – Palestine *
.pt – Portugal *
.pw – Palau
.py – Paraguay
Q
.qa – Qatar
R
.re – Réunion
.ro – Romania *
.rs – Serbia
.ru – Russia *
.rw – Rwanda
S
.sa – Saudi Arabia
.sb – Solomon Islands *
.sc – Seychelles *
.sd – Sudan
.se – Sweden *
.sg – Singapore
.sh – Saint Helena *
.si – Slovenia
.sj – Svalbard and Jan Mayen islands (not in use; no registrations)
.sk – Slovakia
.sl – Sierra Leone
.sm – San Marino *
.sn – Senegal
.so – Somalia * (down, still is delegated to Monolith [ml.org] Philadelphia, an entity defunct since end-1998)
.sr – Suriname *
.st – São Tomé and Príncipe *
.su – Soviet Union (deprecated; being phased out; code "transitionally reserved" by ISO 3166-1)
.sv – El Salvador
.sy – Syria *
.sz – Swaziland *
T
.tc – Turks and Caicos Islands
.td – Chad
.tf – French Southern Territories
.tg – Togo *
.th – Thailand
.tj – Tajikistan *
.tk – Tokelau *
.tl – East Timor (formerly .tp) *
.tm – Turkmenistan *
.tn – Tunisia
.to – Tonga *
.tp – East Timor (deprecated – use .tl; code "transitionally reserved" by ISO 3166-1)
.tr – Turkey
.tt – Trinidad and Tobago *
.tv – Tuvalu *
.tw – Republic of China (Taiwan) *
.tz – Tanzania
U
.ua – Ukraine
.ug – Uganda *
.uk – United Kingdom (code "exceptionally reserved" by ISO 3166-1) (see also .gb)
.us – United States *
.uy – Uruguay
.uz – Uzbekistan
V
.va – Vatican City
.vc – Saint Vincent and the Grenadines *
.ve – Venezuela
.vg – British Virgin Islands *
.vi – United States Virgin Islands
.vn – Vietnam
.vu – Vanuatu *
W
.wf – Wallis and Futuna
.ws – Samoa (formerly Western Samoa) *
Y
.ye – Yemen
.yt – Mayotte
.yu – Yugoslavia (subsequently renamed Serbia and Montenegro)
(code officially replaced by .cs (see above) but still used; code "transitionally reserved" by ISO 3166-1)
Z
.za – South Africa *
.zm – Zambia
.zw – Zimbabwe
Generic top-level domains
A generic top-level domain (gTLD) is a top-level domain used (at least in theory) by a particular class of organization. These are three or more letters long, and are named for the type of organization that they represent (for example, .com for commercial organizations). The following gTLDs currently exist[1] (as does .arpa, which is sometimes considered a gTLD):
.aero - for the air transport industry
.biz - for business use
.cat - for Catalan language/culture
.com - for commercial organizations, but unrestricted
.coop - for cooperatives
.edu - for post-secondary educational establishments
.gov - for governments and their agencies in the United States
.info - for informational sites, but unrestricted
.int - for international organizations established by treaty
.jobs - for employment-related sites
.mil - for the US military
.mobi - for sites catering to mobile devices
.museum - for museums
.name - for families and individuals
.net - originally for network infrastructures, now unrestricted
.org - originally for organizations not clearly falling within the other gTLDs, now unrestricted
.pro - for certain professions
.tel - for services involving connections between the telephone network and the Internet (added March 2, 2007)
.travel - for travel agents, airlines, hoteliers, tourism bureaus, etc.
The following gTLDs are in the process of being approved, and may be added to the root nameservers in the near future:
.asia - for the Asian community
.post - for postal services
.geo - for geographically related sites
.cym - for Welsh language/culture
Unofficial TLDs and proposals
Various organizations and businesses have proposed additional TLDs, and some have created unofficial implementations of them, which are not generally functional. These include .berlin,[3] .sco,[4] .gal,[5] .bzh,[6] and many others.
Pseudo top-level domains
A number of pseudo top-level domains have been defined at various times. Although these pseudo-TLDs look like top-level domains, and serve the same syntactic function in creating names for network endpoints, they have no meaning in the global Domain Name System and are (or were) used only for specialist purposes.
Although they have no official status, they are generally regarded as having been unofficially "grandfathered", and are unlikely ever to be allocated as top-level domains.
Alternative DNS roots
A number of companies have set up their own DNS systems which purport to expand or replace the official DNS root system, and thus to provide their own top-level domains. The article alternative DNS root covers these in more detail.
References
- ^ Generic Top-Level Domains, the Internet Assigned Numbers Authority
Links
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
.com
 |
|
| Introduced | 1985 |
|---|---|
| TLD type | Generic top-level domain |
| Status | Active |
| Registry | VeriSign |
| Sponsor | None |
| Intended use | Commercial entities (worldwide) |
| Actual use | Used for all sorts of sites, commercial or not |
| Registration restrictions | None |
| Structure | Registrations at second level permitted |
| Documents | RFC 920; RFC 1591; ICANN registry agreement |
| Dispute policies | UDRP |
| Web site | VeriSign COM NET Registry |
.com (commercial) is a generic top-level domain (gTLD) used on the Internet's Domain Name System. It was one of the original top-level domains (TLDs), established in January 1985, and has grown to be the largest TLD in use. It was originally administered by the United States Department of Defense. The DoD contracted its maintenance to Stanford Research Institute. On January 1, 1993 the National Science Foundation assumed responsibility for its maintenance, as .com was primarily being used for non-defense interests. The NSF contracted its maintenance to Network Solutions. In 1995 the NSF authorized NSI to begin charging registrants (of .org and .net as well as .com) an annual fee, for the first-time since its inception. Initially it was $50 per year, with $35 going to NSI, and $15 going to a government fund. New registrations had to pay for the first two years, making the new-domain registration fee $100. In 1997 the United States Department of Commerce assumed authority over it (along with the rest of the generic top level domains). It is currently operated by VeriSign, which had acquired Network Solutions. (VeriSign later spun off Network Solutions' non-registry functions into the current company which continues as a registrar.) In the English language it is consistently pronounced as a word, dot-com, and has entered common parlance this way.
Although .com domains are officially intended to designate commercial entities (others such as government agencies or educational institutions have different top-level domains assigned to them), there has been no restriction on who can register .com domains since the mid-1990s. The opening of the .com registry to the public coincided with the commercialization and popularization of the Internet, and .com quickly became the most common top-level domain for websites. Many companies which flourished in the period between 1997-2001 (the time known as the "dot-com bubble") went so far as to incorporate .com into the company name; these became known as dot-coms or dot-com companies. The introduction of .biz in 2001, which is restricted to businesses, has had little impact on the popularity of .com.
Although companies anywhere in the world can register .com domains, many countries have a second-level domain with a similar purpose under their own ccTLD. Such second-level domains are usually of the form .com.xx or .co.xx, where xx is the ccTLD. Argentina (.com.ar), Japan (.co.jp), New Zealand (.co.nz), India (.co.in), the People's Republic of China (.com.cn), Pakistan (.com.pk), and the United Kingdom (.co.uk) are all examples.
Many noncommercial sites, such as those of nonprofit organizations or governments, use .com addresses. Some consider this to be contrary to the domain's original purpose and might say that a .org, .gov, or other more specific TLD might be more appropriate for such sites. However, many organizations prefer the recognizability of a .com domain to a less familiar one. As well, the original purposes of many of the top level domains have become irrelevant without restrictions on registrations.
Registrations are processed via registrars accredited by ICANN; internationalized domain names are also accepted.
Transfer Procedures
Domains can be transferred between registrars. Prior to October 2006 the procedure used by Verisign was complex and unreliable - requiring a notary public to verify the identity of the registrant requesting a domain transfer. In October 2006, a new procedure, requiring the losing registrar to provide an authorization code on instruction from the registrant (also known as EPP code) was introduced by Verisign to reduce the incidence of domain hijacking.
List of oldest .com domains
The following are the 100 oldest still-existing registered .com domains [1]:
Rank Create date Domain name
1 March 15, 1985 symbolics.com |
Rank Create date Domain name
50 December 11, 1986 CCUR.com |
Links
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
Pseudo top-level domains
A number of pseudo top-level domains to be used in naming computers have been defined at various times. These "pseudo-TLDs" include .bitnet, .csnet, .local, .onion and .uucp. Although these pseudo-TLDs look like top-level domains, and serve the same syntactic function in creating names for network endpoints, they have no meaning in the global Domain Name System and are (or were) used only for specialist purposes; typically for addressing machines that were not reachable via the Internet Protocol for use in services such as E-mail and Usenet via UUCP.
Although they have no official status, they are generally regarded as having been unofficially "grandfathered", and are unlikely ever to be allocated as top-level domains.
.arpa is unique in having been a pseudo-top-level domain, formerly used by ARPA, that has now become a real top-level domain that is defined in the Internet DNS root for use as an infrastructure top-level domain.
Sponsored top-level domains
A sponsored top-level domain is a generic top-level domain proposed by an independent agency, with that agency establishing and enforcing rules restricting the eligibility of registrants to use the TLD. For example, the .aero TLD is sponsored by the Société Internationale de Télécommunications Aéronautiques, who limits registrations to members of the air-transport industry.
| TLD | Eligibility | Sponsors |
|---|---|---|
| Current sponsored TLDs | ||
| .aero | Members of the air-transport industry | Société Internationale de Télécommunications Aéronautiques |
| .coop | Cooperative associations | Dot Cooperation LLC |
| .museum | Museums | Museum Domain Management Association |
| .pro | Credentialed professionals and related entities | Registry Services Corporation |
| .travel | Travel agents, airlines, hoteliers, tourism bureaus, etc. | The Travel Partnership |
| .cat | Catalan language and culture | |
| .jobs | Employment-related sites | |
| .mobi | Mobile devices and services for them | |
| .tel | Internet-based voice/data/text communication | Telname Limited |
| Pending sponsored TLDs | ||
| .post | Postal agencies and similar businesses | Universal Postal Union |
| Rejected sponsored TLDs | ||
| .xxx | Sexually explicit material | ICM Registry, Inc |
There are also non-sponsored generic TLDs which are restricted by other criteria, including .edu (United States accredited colleges), .mil (the United States military), .gov (the United States government), .int (organisations formed by international treaty), and .biz (businesses engaging in commerce on the internet).
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
Top-level domains
A top-level domain (TLD) is the last part of an Internet domain name; that is, the letters which follow the final dot of any domain name. For example, in the domain name www.example.com, the top-level domain is com (or COM, as domain names are not case-sensitive).
The Internet Assigned Numbers Authority (IANA), operated by by the Internet Corporation for Assigned Names and Numbers (ICANN), currently classifies top-level domains into the following types:
- country code top-level domains (ccTLD): Used by a country or a dependent territory. It is two letters long, for example .us for the United States.
- generic top-level domains (gTLD): Used (at least in theory) by a particular class of organizations (for example, .com for commercial organizations). It is three or more letters long. Most gTLDs are available for use worldwide, but for historical reasons .mil (military) and .gov (governmental) are restricted to use by the respective U.S. authorities. gTLDs are subclassified into sponsored top-level domains (sTLD), e.g. .aero, .coop and .museum, and unsponsored top-level domains (uTLD), e.g. .biz, .info, .name and .pro.
- infrastructure top-level domains (iTLD): The top-level domain .arpa is the only confirmed one. .root has been known to exist without reason.
Historical TLDs
A .nato was added in the late 1980s by the NIC for the use of NATO, who felt that none of the then existing TLDs adequately reflected their status as an international organization. Soon after this addition, however, the NIC created the .int TLD for the use of international organizations, and convinced NATO to use nato.int instead. However, the nato TLD, although no longer used, was not deleted until July 1996.
Other historical TLDs are .cs for Czechoslovakia, .zr for Zaire and .dd for East Germany. In contrast to these, the TLD .su has remained in active use despite the demise of the Soviet Union that it represents.
Pseudo-domains
In the past the Internet was just one of many wide-area computer networks. Computers not connected to the Internet, but connected to another network such as BITNET, CSNET or UUCP, could generally exchange e-mail with the Internet via e-mail gateways. When used on the Internet, addresses on these networks were often placed under pseudo-domains such as bitnet, csnet and uucp; however these pseudo-domains implemented in mail server configurations such as sendmail.cf and were not real top-level domains and did not exist in DNS.
Most of these networks have long since ceased to exist, and although UUCP still gets significant use in parts of the world where Internet infrastructure has not yet become well-established, it subsequently transitioned to using Internet domain names, so pseudo-domains now largely survive as historical relics.
The anonymity network Tor has a pseudo-domain onion, which can only be reached with a Tor client because it uses the Tor-protocol (onion routing) to reach the hidden service in order to protect the anonymity of the domain.
.local deserves special mention as it is required by the Zeroconf protocol. It is also used by many organizations internally, which will become a problem for those users as Zeroconf becomes more popular. Both .site and .internal have been suggested for private usage, but no consensus has yet emerged.
Reserved TLDs
RFC 2606 reserves the following four top-level domain names for various purposes, with the intention that these should never become actual TLDs in the global DNS:
- example — reserved for use in examples
- invalid — reserved for use in obviously invalid domain names
- localhost — reserved to avoid conflict with the traditional use of localhost
- test — reserved for use in tests
TLDs in alternative roots
Alternative DNS roots have their own sets of TLDs. See that article for details. At times, browser plugins have been developed to allow access to some set of "alternative" domain names even when the normal DNS roots are otherwise used.
References
- Addressing the World: National Identity and Internet Country Code Domains, edited by Erica Schlesinger Wass (Rowman & Littlefield, 2003, ISBN 0-7425-2810-3) [1], examines connections between cultures and their ccTLDs.
- Ruling the Root by Milton Mueller (MIT Press, 2001, ISBN 0-262-13412-8) [2], discusses TLDs and domain name policy more generally.
Links
- Articles on CircleID about Top-Level Domains
- The ICANNwiki focuses on domain name allocation.
- TLD Statistics
- IANA TLD List
- Southern Hemisphere TLDs
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
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Video: dotPARIS Top-Level-Domains at ICANN Paris 2008
List of Internet top-level domains
The following is a list of currently existing Internet Top-level domains (TLDs).
| iTLD | Entity | Notes |
|---|---|---|
| .arpa | Address and Routing Parameter Area | This is an internet infrastructure TLD. |
| .root | N/A | Diagnostic marker to indicate a root zone load was not truncated. |
| gTLD | Entity | Notes |
| .aero | air-transport industry | Must verify eligibility for registration; only those in various categories of air-travel-related entities may register. |
| .asia | Asia-Pacific region | This is a TLD for companies, organizations, and individuals based in the region of Asia, Australia, and the Pacific. |
| .biz | business | This is an open TLD; any person or entity is permitted to register; however, registrations may be challenged later if they are not by commercial entities in accordance with the domain's charter. |
| .cat | Catalan | This is a TLD for websites in the Catalan language or related to Catalan culture. |
| .com | commercial | This is an open TLD; any person or entity is permitted to register. |
| .coop | cooperatives | The .coop TLD is limited to cooperatives as defined by the Rochdale Principles. |
| .edu | educational | The .edu TLD is limited to institutions of learning (mostly U.S.), such as 2 and 4-year colleges and universities. |
| .gov | governmental | The .gov TLD is limited to U.S. governmental entities and agencies (commonly federal-level). |
| .info | information | This is an open TLD; any person or entity is permitted to register. |
| .int | international organizations | The .int TLD is strictly limited to organizations, offices, and programs which are endorsed by a treaty between two or more nations. |
| .jobs | companies | The .jobs TLD is designed to be added after the names of established companies with jobs to advertise. At this time, owners of a "company.jobs" domain are not permitted to post jobs of third party employers. |
| .mil | United States Military | The .mil TLD is limited to use by the U.S. military. |
| .mobi | mobile devices | Must be used for mobile-compatible sites in accordance with standards. |
| .museum | museums | Must be verified as a legitimate museum. |
| .name | individuals, by name | This is an open TLD; any person or entity is permitted to register; however, registrations may be challenged later if they are not by individuals (or the owners of fictional characters) in accordance with the domain's charter |
| .net | network | This is an open TLD; any person or entity is permitted to register. |
| .org | organization | This is an open TLD; any person or entity is permitted to register. |
| .pro | professions | Currently, .pro is reserved for licensed doctors, attorneys, and certified public accountants only. A professional seeking to register a .pro domain must provide their registrar with the appropriate credentials. |
| .tel | Internet communication services | |
| .travel | travel and travel-agency related sites | Must be verified as a legitimate travel-related entity. |
ccTLD Country/dependency/region Notes
.ac Ascension Island
.ad Andorra
.ae United Arab Emirates
.af Afghanistan
.ag Antigua and Barbuda
.ai Anguilla
.al Albania
.am Armenia
.an Netherlands Antilles
.ao Angola
.aq Antarctica Defined as per the Antarctic Treaty as everything south of latitude 60°S
.ar Argentina
.as American Samoa
.at Austria
.au Australia Includes Ashmore and Cartier Islands and Coral Sea Islands
.aw Aruba
.ax Åland
.az Azerbaijan
.ba Bosnia and Herzegovina
.bb Barbados
.bd Bangladesh
.be Belgium
.bf Burkina Faso
.bg Bulgaria
.bh Bahrain
.bi Burundi
.bj Benin
.bm Bermuda
.bn Brunei Darussalam
.bo Bolivia
.br Brazil
.bs Bahamas
.bt Bhutan
.bv Bouvet Island Not in use (Norwegian dependency; see .no)
.bw Botswana
.by Belarus
.bz Belize
.ca Canada
.cc Cocos (Keeling) Islands
.cd Democratic Republic of the Congo Formerly Zaire
.cf Central African Republic
.cg Republic of the Congo
.ch Switzerland (Confoederatio Helvetica)
.ci Côte d'Ivoire
.ck Cook Islands
.cl Chile
.cm Cameroon
.cn China, mainland Mainland China only: Hong Kong and Macau use separate TLDs.
.co Colombia
.cr Costa Rica
.cu Cuba
.cv Cape Verde
.cx Christmas Island
.cy Cyprus
.cz Czech Republic
.de Germany (Deutschland)
.dj Djibouti
.dk Denmark
.dm Dominica
.do Dominican Republic
.dz Algeria (Dzayer) Not available for private use
.ec Ecuador
.ee Estonia
.eg Egypt
.er Eritrea
.es Spain (España)
.et Ethiopia
.eu European Union Restricted to companies and individuals in the European Union
.fi Finland
.fj Fiji
.fk Falkland Islands
.fm Federated States of Micronesia Used for some radio related websites outside Micronesia
.fo Faroe Islands
.fr France Can only be used by organisations or persons with a presence in France.
.ga Gabon
.gb Great Britain Seldom used; the primary ccTLD used is .uk for United Kingdom
.gd Grenada
.ge Georgia
.gf French Guiana
.gg Guernsey
.gh Ghana
.gi Gibraltar
.gl Greenland
.gm The Gambia
.gn Guinea
.gp Guadeloupe
.gq Equatorial Guinea
.gr Greece
.gs South Georgia and the South Sandwich Islands
.gt Guatemala
.gu Guam
.gw Guinea-Bissau
.gy Guyana
.hk Hong Kong Special administrative region of the People's Republic of China.
.hm Heard Island and McDonald Islands
.hn Honduras
.hr Croatia (Hrvatska)
.ht Haiti
.hu Hungary
.id Indonesia
.ie Ireland (Éire)
.il Israel
.im Isle of Man
.in India Under INRegistry since April 2005 except: gov.in, mil.in, ac.in, edu.in, res.in
.io British Indian Ocean Territory
.iq Iraq
.ir Iran
.is Iceland (Ísland)
.it Italy Restricted to companies and individuals in the European Union
.je Jersey
.jm Jamaica
.jo Jordan
.jp Japan
.ke Kenya
.kg Kyrgyzstan
.kh Cambodia (Khmer)
.ki Kiribati
.km Comoros
.kn Saint Kitts and Nevis
.kr South Korea
.kw Kuwait
.ky Cayman Islands
.kz Kazakhstan
.la Laos Currently being marketed as the official domain for Los Angeles.
.lb Lebanon
.lc Saint Lucia
.li Liechtenstein
.lk Sri Lanka
.lr Liberia
.ls Lesotho
.lt Lithuania
.lu Luxembourg
.lv Latvia
.ly Libya
.ma Morocco Used for a couple of Hungarian language websites, because in Hungarian 'ma' means 'today'.
.mc Monaco
.md Moldova
.mg Madagascar
.mh Marshall Islands
.mk Republic of Macedonia
.ml Mali
.mm Myanmar
.mn Mongolia
.mo Macau Special administrative region of the People's Republic of China.
.mp Northern Mariana Islands
.mq Martinique
.mr Mauritania
.ms Montserrat
.mt Malta
.mu Mauritius
.mv Maldives
.mw Malawi
.mx Mexico
.my Malaysia
.mz Mozambique
.na Namibia
.nc New Caledonia
.ne Niger
.nf Norfolk Island
.ng Nigeria
.ni Nicaragua
.nl Netherlands
.no Norway Must be registered with a company in Norway to register.
.np Nepal
.nr Nauru
.nu Niue Commonly used for Scandinavian and Dutch websites, because in those languages 'nu' means 'now'.
.nz New Zealand
.om Oman
.pa Panama
.pe Peru
.pf French Polynesia With Clipperton Island
.pg Papua New Guinea
.ph Philippines
.pk Pakistan
.pl Poland
.pm Saint-Pierre and Miquelon
.pn Pitcairn Islands
.pr Puerto Rico
.ps Palestinian territories PA-controlled West Bank and Gaza Strip
.pt Portugal Only available for Portuguese registered brands and companies
.pw Palau
.py Paraguay
.qa Qatar
.re Réunion
.ro Romania
.ru Russia
.rw Rwanda
.sa Saudi Arabia
.sb Solomon Islands
.sc Seychelles
.sd Sudan
.se Sweden
.sg Singapore
.sh Saint Helena
.si Slovenia
.sj Svalbard and Jan Mayen Islands Not in use (Norwegian dependencies; see .no)
.sk Slovakia
.sl Sierra Leone
.sm San Marino
.sn Senegal
.so Somalia
.sr Suriname
.st São Tomé and Príncipe
.su former Soviet Union Still in use
.sv El Salvador
.sy Syria
.sz Swaziland
.tc Turks and Caicos Islands
.td Chad
.tf French Southern and Antarctic Lands
.tg Togo
.th Thailand
.tj Tajikistan
.tk Tokelau Also used as a free domain service to the public
.tl East Timor Old code .tp is still in use
.tm Turkmenistan
.tn Tunisia
.to Tonga
.tp East Timor ISO code has changed to TL; .tl is now assigned but .tp is still in use
.tr Turkey
.tt Trinidad and Tobago
.tv Tuvalu Much used by television broadcasters. Also sold as advertising domains
.tw Taiwan, Republic of China Used in the Republic of China, namely Taiwan, Penghu, Kinmen, and Matsu.
.tz Tanzania
.ua Ukraine
.ug Uganda
.uk United Kingdom
.um United States Minor Outlying Islands
.us United States of America Commonly used by U.S. State and local governments instead of .gov TLD
.uy Uruguay
.uz Uzbekistan
.va Vatican City State
.vc Saint Vincent and the Grenadines
.ve Venezuela
.vg British Virgin Islands
.vi U.S. Virgin Islands
.vn Vietnam
.vu Vanuatu
.wf Wallis and Futuna
.ws Samoa Formerly Western Samoa
.ye Yemen
.yt Mayotte
.yu Yugoslavia Now used for Serbia and Montenegro
.za South Africa (Zuid-Afrika)
.zm Zambia
.zw Zimbabwe
Links
Legal users of domains and politics
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 the United States' political influence over ICANN. This was a significant issue in the attempt to create a .xxx top-level domain and sparked greater interest in alternative DNS roots that would be beyond the control of any single country.
Truth in Domain Names 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.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
Hostname
A hostname (occasionally also, a sitename) is the unique name by which a network-attached device (which could consist of a computer, file server, network storage device, fax machine, copier, cable modem, etc.) is known on a network. The hostname is used to identify a particular host in various forms of electronic communication such as the World Wide Web, e-mail or Usenet.
On the Internet, the terms "hostname" and "domain name" are often used interchangeably, but there are subtle technical differences between them.
Overview
Hostnames are used by various naming systems, NIS, DNS, SMB, etc., and so the meaning of the word hostname will vary depending on naming system in question, which in turn varies by type of network. A hostname meaningful to a Microsoft NetBIOS workgroup may be an invalid Internet hostname. When presented with a hostname and no context, it is usually safe to assume that the network is the Internet and DNS is the hostname's naming system.
Host names are typically used in an administrative capacity and may appear in computer browser lists, active directory lists, IP address to hostname resolutions, email headers, etc. They are human-readable nick-names, which ultimately correspond to unique network hardware MAC addresses. In some cases the host name may contain embedded domain names and/or locations, non-dotted IP addresses, etc.
On a simple local area network, a hostname is usually a single word: for instance, an organization's CVS server might be named "cvs" or "server-1".
Internet hostnames
On the Internet, a hostname is a domain name assigned to the host. This is usually a combination of the host's local name with its parent domain's name. For example, "en.wikipedia.org" consists of a hostname ("en") and the domain name "wikipedia.org". This kind of hostname is translated into an IP address via the local hosts file, or the Domain Name System (DNS) resolver. It is possible for a single host to have several hostnames; but generally the operating system of the host prefers to have one hostname that the host uses for itself.
Any domain name can also be hostname, as long as the restrictions mentioned below are followed. So, for example, both "en.wikimedia.org" and "wikimedia.org" are hostnames because they both have IP addresses assigned to them. The domain name "pmtpa.wikimedia.org" is not a hostname since it does not have an IP address, but "rr.pmtpa.wikimedia.org" is a hostname. All hostnames are domain names, but not all domain names are hostnames.
Restrictions on valid host names
Hostnames, like all domain names, are made up of a series of "labels", with each label being separated by a dot. Each label must be between 1 and 63 characters long, and there is a maximum of 255 characters when all labels are combined.
Unlike domain names, hostname labels can only be made up of the ASCII letters 'a' through 'z' (case-insensitive), the digits '0' through '9', and the hyphen. Labels can not start nor end with a hyphen. Special characters other than the hyphen (and the dot between labels) are not allowed, although they are sometimes used anyway. Underscore characters are commonly used by Windows systems but according to RFC 952 they are not allowed and several systems, such as DomainKeys and the SRV record deliberately use the underscore to make sure their special domain names are not confused with a hostname. Since some systems will check to make sure that hostnames contain only valid characters and others do not, the use of the invalid characters such as the underscore has caused many subtle problems in systems that connect to the wider world.
So, the hostname "en.wikipedia.org" is made up of the DNS labels "en", "wikipedia" and "org". Labels such as "2600" and "3com" can be used in hostnames, but "-hi-" and "*hi*" are invalid.
A hostname is considered to be a fully qualified domain name (FQDN) if all the labels up to and including the top-level domain name (TLD) are specified. Depending on the system, an unqualified hostname such as "compsci" or "wikipedia" may be combined with default domain names in order to determine the fully qualified domain name. So, a student at Harvard may be able to send mail to "joe@compsci" and have it sent to compsci.harvard.edu.
Choosing host names
General guidelines on choosing a good hostnames are outlined in RFC 1178. The folklore interest of hostnames stems from the creativity and humour they often display. Interpreting a sitename is not unlike interpreting a vanity licence plate; one has to mentally unpack it, allowing for mono-case and length restrictions and the lack of whitespace. Hacker tradition deprecates dull, institutional-sounding names in favour of punchy, humorous, and clever coinages (except that it is considered appropriate for the official public gateway machine of an organisation to bear the organisation's name or acronym). Mythological references, cartoon characters, animal names, and allusions to sci-fi or fantasy literature are probably the most popular sources for sitenames (in roughly descending order). The obligatory comment is Harris's lament: "All the good ones are taken!"
It is often possible to guess a hostname for a particular institution. This is useful if you want to know if they operate network services like anonymous FTP, World-Wide Web or finger. First try the institution's name or obvious abbreviations thereof, with the appropriate domain appended, e.g. "mit.edu". If this fails, prepend "ftp." or "www." as appropriate, e.g. "www.data-io.com". You can use the ping command as a quick way to test whether a hostname is valid.
Notes and references
- ^ Host name vs domain name explanation from the DNS OP IETF Working Group
Links
- RFC 952 - "DoD Internet host table specification."
- RFC 1034 - "DOMAIN NAMES - CONCEPTS AND FACILITIES" (In particular, section 3.5)
- RFC 1035 - "DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION" (In particular, section 2.3.1)
- RFC 1123 - "Requirements for Internet Hosts - Application and Support."
- RFC 1178 - "Choosing a Name for Your Computer"
- RFC 3696 - "Application Techniques for Checking and Transformation of Names"
- web-based tools working with hostnames at the Open Directory Project
This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
Domain name registry
A domain name registry, also called Network Information Centre (NIC), is part of the Domain Name System (DNS) of the Internet which converts domain names to IP addresses. It is an organisation that manages the registration of Domain names within the top-level domains for which it is responsible, controls the policies of domain name allocation, and technically operates its top-level domain.
Domain names are managed under a hierarchy headed by the Internet Assigned Numbers Authority (IANA), which manages the top of the DNS tree by administrating the data in the root nameservers.
IANA also operates the .int registry for intergovernmental organisations, the .arpa zone for protocol administration purposes, and other critical zones such as root-servers.net.
IANA delegates all other domain name authority to other domain name registries such as VeriSign.
Country code top-level domains (ccTLD) are delegated by IANA to national registries such as DENIC in Germany, or Nominet in the United Kingdom.
Operation
Some name registries are government departments (e.g., the registry for the Vatican www.nic.va ). Some are co-operatives of internet service providers (such as DENIC) or not-for profit companies (such as Nominet UK). Others operate as commercial organizations, such as the US registry (www.nic.us).
The allocated and assigned domain names are made available by registries by use of the Whois system and via their Domain name servers.
Some registries sell the names directly (like SWITCH in Switzerland) and others rely solely on registrars to sell them.
Policies
Allocation policies
Generally, domain name registries operate a first-come-first-served system of allocation but may reject the allocation of specific domains on the basis of political, religious, historical, legal or cultural reasons.
For example, in the United States, between 1996 and 1998, InterNIC automatically rejected domain name applications based on a list of perceived obscenities.
Registries may also control matters of interest to their local communities: for example, the German, Japanese and Polish registries have introduced internationalized domain names to allow use of local non-ASCII characters.
Dispute policies
Domains which are registered with ICANN generally have to use the Uniform Domain-Name Dispute-Resolution Policy (UDRP), however, DENIC requires people to use the German civil courts, and Nominet UK deals with Intellectual Property and other disputes through its own dispute resolution service.
Cost of registration
The cost of domain registration is set by each individual registry.
Second-level domains
Domain name registries may also impose a system of second-level domains on users. DENIC, the registry for Germany (.de), does not impose second level domains. AFNIC, the registry for France (.fr), has some second level domains, but not all registrants have to use them, and Nominet UK, the registry for the United Kingdom (.uk), requires all names to have a second level domain.
Registrants of second-level domains sometimes act as a registry by offering sub-registrations to their registration. For example, registrations to .fami.ly are offered by the registrant of fami.ly and not by GPTC, the registry for Libya (.ly).
Links
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
Domain name registrars
A domain name registrar is a company accredited by the Internet Corporation for Assigned Names and Numbers (ICANN) and/or by a national ccTLD authority to register Internet domain names. ICANN has authority over gTLDs, or Generic Top Level Domains. Examples of gTLDs include .com, .net and .org. ICANN does not have authority over ccTLDs, or Country Code Top-Level Domains, though it is quite common for domain name registrars to offer ccTLD registration services as well. Most registrars provide DNS hosting service, but this is not required, and is often considered a separate service.
History
Until 1999, there was no Shared Registration System (SRS). Network Solutions (NSI) operated the .com, .net, and .org registries, and was the de jure registrar and registry. However, several companies had set up as de facto registrars, including NetNames, who invented the idea of a commercial standalone domain name registration service in 1996. Registrars formed another link in the food chain, introducing the concept of domain name sales, effectively introducing the wholesale model into the industry. NSI followed suit, forcing the issue of separation of Registry and Registrar. In October 1998, following pressure from the growing domain name registration business and other interested parties, NSI's agreement with the US Department of Commerce was amended, requiring the creation of an SRS that supported multiple registrars. The SRS officially opened on November 30, 1999 under the supervision of ICANN, though there had been several testbed registrars using the system since March 11, 1999. Since then, over 500 registrars have entered the market for domain name registration services.
Designated registrar
An end-user alone, cannot register and manage their domain name information with ICANN. A designated registrar must be chosen to have one's domain names registered and managed with ICANN on their behalf. Prior to 1999, the only .com registrar was NSI, but after the approval of the SRS, this opened up the opportunity for other companies to be designated as registrars.
Only one designated registrar may modify or delete information about a domain name. The competition that SRS created enables the end user to choose from many registrars offering different services at varying prices. It is not unusual for an end user to wish to switch registrars. Thus, there is the domain name transfer clause.
When a registrar registers a .com domain name for the end-user, it must pay a maximum annual fee of US$6.00 to VeriSign and a US$0.25 administration fee to ICANN. VeriSign is the registry manager for .com gTLD. Low cost bulk registrars like Go Daddy and Tucows must manage their margin after paying these fees and their equipment cost. Therefore, the barrier for entry into the bulk registrar industry is high for new companies without an existing customer base.
Domain name transfers
Domain name transfers is the act of designating a new registrar with the authority to add, modify, and delete information about the domain name. The usual process of a domain name transfer is:
- The end user contacts the new registrar with the wish to transfer the domain name to their service
- The new registrar will contact the old registrar with this information
- The old registrar will contact the end user to confirm the authenticity of this request
- The old registrar will release authority to the new registrar
- The new registrar will notify the end user of transfer completion
After this process, the new registrar becomes one's designated registrar and all correspondence shall be done with them.
Transfer scams
With the introduction of SRS, many smaller registrars had to compete with the de facto standard, NSI. Some companies offered value added services or used viral marketing. Some companies decided to trick customers to switch from NSI - akin to what some phone companies do to get new customers.
Many of these transfer scams involve a notice sent in the mail, fax, or e-mail. Some scammers may even call by phone (as the contact information is available through WHOIS) to harvest more information. These notices would include information publicly available from the WHOIS database to add to the look of authenticity. The text would include legalese to confuse the end user into thinking that it is an official binding document. If one receives such document, one should notify the resident "computer guy" or IT support person.
Scam registrars go after domain names that are expiring soon or have recently expired. Expired domain names do not have to go through the authentication process to be transferred, as the previous registrar would have relinquished management rights of the domain name. Domain name expiry dates are readily available via WHOIS.
Links
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.