Subdomain
Encyclopedia
In the Domain Name System
(DNS) hierarchy, a subdomain is a domain
that is part of a larger domain.
(DNS) has a tree structure
or hierarchy, with each node on the tree being a domain name
. A subdomain is a domain that is part of a larger domain, the only domain that is not also a subdomain is the root domain. For example, mail.example.com and calendar.example.com are subdomains of the example.com domain, which in turn is a subdomain of the com top-level domain
(TLD).
A "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 DNS 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.
is a subdomain of an ISP's domain that is aliased to an individual user account, or a subdomain that expresses the individuality of the person on whose behalf it is registered.
, or a service provided by a number of machines in a cluster. Some websites use different subdomains to point to different server clusters. For example, www.example.com
points to Server Cluster 1 or Datacentre 1, and www2.example.com points to Server Cluster 2 or Datacentre 2, etc.
Domain name system
The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...
(DNS) hierarchy, a subdomain is a domain
Domain name
A domain name is an identification string that defines a realm of administrative autonomy, authority, or control in the Internet. Domain names are formed by the rules and procedures of the Domain Name System ....
that is part of a larger domain.
Overview
The Domain Name SystemDomain name system
The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...
(DNS) has a tree structure
Tree structure
A tree structure is a way of representing the hierarchical nature of a structure in a graphical form. It is named a "tree structure" because the classic representation resembles a tree, even though the chart is generally upside down compared to an actual tree, with the "root" at the top and the...
or hierarchy, with each node on the tree being a domain name
Domain name
A domain name is an identification string that defines a realm of administrative autonomy, authority, or control in the Internet. Domain names are formed by the rules and procedures of the Domain Name System ....
. A subdomain is a domain that is part of a larger domain, the only domain that is not also a subdomain is the root domain. For example, mail.example.com and calendar.example.com are subdomains of the example.com domain, which in turn is a subdomain of the com top-level domain
Top-level domain
A top-level domain is one of the domains at the highest level in the hierarchical Domain Name System of the Internet. The top-level domain names are installed in the root zone of the name space. For all domains in lower levels, it is the last part of the domain name, that is, the last label of a...
(TLD).
A "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 DNS 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
Domain name registry
A domain name registry is a database of all domain names registered in a top-level domain. A registry operator, also called a network information center , is the part of the Domain Name System of the Internet that keeps the database of domain names, and generates the zone files which convert...
have shorter limits than that.
Uses
Subdomains are commonly used by organizations that wish to assign a unique name to a particular department, function, or service related to the organization. For example, a university might assign "cs" to the computer science department, such that a number of hosts could be used inside that subdomain, such as mail.cs.example.edu or www.cs.example.edu.Vanity domain
A vanity domainVanity domain
In the Domain Name System , a vanity domain is a domain name whose purpose is to express the individuality of the person on whose behalf it is registered. This contrasts with domain names which resolve to an organisation or a service that organisation offers...
is a subdomain of an ISP's domain that is aliased to an individual user account, or a subdomain that expresses the individuality of the person on whose behalf it is registered.
Server cluster
Depending on application, a record inside a domain, or subdomain might refer to a hostnameHostname
A hostname is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication such as the World Wide Web, e-mail or Usenet...
, or a service provided by a number of machines in a cluster. Some websites use different subdomains to point to different server clusters. For example, www.example.com
Example.com
Example.com, example.net, example.org, and example.edu are second-level domain names reserved for documentation purposes and examples of the use of domain names....
points to Server Cluster 1 or Datacentre 1, and www2.example.com points to Server Cluster 2 or Datacentre 2, etc.