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Subdomain

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Title: Subdomain  
Author: World Heritage Encyclopedia
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Subject: Domain name, Operation Protect Our Children, Wildcard certificate, NTP pool, WWW2
Collection: Domain Name System
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Subdomain

In the Domain Name System (DNS) hierarchy, a subdomain is a domain that is a part of a main domain.[1]

Contents

  • Overview 1
  • Uses 2
    • Vanity domain 2.1
    • Server cluster 2.2
      • Subdomains vs. Directories 2.2.1
  • See also 3
  • References 4

Overview

The 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 most domain registries limit at 253 characters.

Subdomains in this context are defined by editing the DNS zone file pertaining to the parent domain. However, there is a lively debate over the use of the term “subdomain” when referring to names which map to the Address record (A; host) and various other types of zone records which may map to any public IP address destination and any type of server. Certain groups insist that it is inappropriate to use the term “subdomain” to refer to any mapping other than that provided by zone NS (name server) records and any server-destination other than that of a domain name server. Notwithstanding the terminology debate, many prominent public DNS providers use the term “subdomain” to refer to names which map to A (host) records which may map to any type of host or destination-server.

Uses

In the United Kingdom, the third-level domain names are standard and branch off from the second-level domains. For example:

Subdomains are also 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 domain 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 hostname, 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..

Some domains host their nameservers as ns1.example.com, ns2.example.com, etc., and these usually never show up in search engine results.

Subdomains vs. Directories

example.com/yn points to a directory within the example.com domain, not to a subdomain of example.com.

See also

References

  1. ^ a b  
  2. ^ "BBC News - UK court systems set to adopt judiciary.uk domain names". BBC News. 23 November 2011. Retrieved 26 February 2014. 
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