Subdomain
Domaining Guide
Subdomain
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In the
Domain Name System (DNS) hierarchy, a subdomain is a
domain that is part of a larger domain. For example, "example.com"
is a subdomain of the "com"
top-level domain (TLD) while "www.example.com" is a service in the
domain "example.com". In fact, the "com" TLD is a subdomain of the
root domain, ".". This hierarchical organisation is similar to that in a
filesystem; something is a subdomain if it could be equated to a
folder, and a record within that subdomain to a file. Note, though, that
DNS names are written in descending hierarchy right-to-left, where
filesystems are written left-to-right.
Relative to a subdomain, the larger domain that it is a part of is its
parent domain, or alternately superdomain (the former term appears to
be preferred by the
IETF).
A subdomain is sometimes termed a
vanity domain, especially when it is a subdomain of an ISP's own domain
aliased to an individual user account. However, the term "vanity domain" has
other usages, discussed at that article.
Some websites use a different
Host name
to point to different servers in a 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.
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.
Depending on application, a record inside a domain, or subdomain might refer
to a Host
name, or a service provided by a number of machines in a cluster.
See also
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Domain name
Hostname
Fully qualified domain name
Internationalized domain name
Subdomain
Domain name registry
WHOIS
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