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The '''Second Level Domain''', or '''SLD''', is generally the portion of the [[URL]] that identifies the actual website's domain name.<ref>[http://www.build-your-website.co.uk/choosing-domain-name-second-level.htm SLD]</ref>
The '''Second Level Domain''', or '''SLD''', is the data directly before the top-level domain ([[TLD]]).<ref>[http://www.giantgeek.com/blog/?p=97 What is a SLD]</ref> For example, in www.example.com, “example” represents the second level domain, as the suffix "(dot)-com" represents the [[TLD]]. The SLD is generally the portion of the [[URL]] that identifies the website's domain name.<ref>[http://www.build-your-website.co.uk/choosing-domain-name-second-level.htm SLD]</ref> Usually, the SLD is determined and defined upon registration of a domain name. More than one SLD can function on the same [[Internet Protocol|IP]] Address.<ref>[http://help.godaddy.com/article/335 SLD Definition]</ref>


==Overview==
The DNS is composed of a tree-like hierarchy. Each TLD includes many second-level domains (such as "example" in "www.example.com"); each second-level domain can include a number of third-level domains ("www" in "www.example.com"), and so on.
Technically, the second domain level is the data directly before the top-level domain ([[TLD]]).<ref>[http://www.giantgeek.com/blog/?p=97 What is a SLD]</ref>
For example, in www.domainname.com, “domainname” represents the second level domain. Whereas the suffix "(dot)-com" represents the [[TLD]].
 
Usually, the SLD is determined and defined upon registration of a domain name. More than one SLD can function on the same [[Internet Protocol|IP]] Address.<ref>[http://help.godaddy.com/article/335 SLD Definition]</ref>


==2LDs==
===ccSLDs===
===ccSLDs===
A ccSLD, or Country Code Second Level Domain, refers to when an additional prefix is added to a ccTLD. An example of this would be .co.uk, where .uk is the (cc)TLD and .uk is the (cc)SLD. In this circumstance, the domain name ("example" in "example.co.uk") would be considered the third level domain, as it is in the third position.<ref>[http://www.igoldrush.com/reference/domain-glossary/c/ccsld-country-code-second-level-domain iGoldrush Domain Glossary]</ref> This can become confusing, as the domain name is commonly equated with the second level domain, and the [[Subdomain|subdomain]] is commonly equated with the third level domain.
Some countries restrict the second level under their [[ccTLD]]. These countries require that the second-level domain be one of several pre-determined second-level domains, generally indicating what type of individual or organization may register under that SLD. For these countries, you are not permitted to register domain names under the top level domain. It must be registered under one of the pre-determined second-level domains, called a ccSLD, or Country Code Second Level Domain.<ref>[http://www.quackit.com/domain-names/second-level_domain_names.cfm Second-Level Domain Names, quack-it.com]</ref>
 
===Functional SLDs===
A Functional SLD is a reasonable equivalent to an SLD in a namespace where domain names as second level domains are not permitted for policy reasons.
 
An example of a Functional SLD would be foo.com.au. While .com is the actual [[SLD]], [[.au]] policy does not permit the widespread registration of second level domains, thereby creating a proliferation of Functional SLDs (in this case .foo) in the [[.au]] namespace.<ref>[http://tools.ietf.org/html/draft-ietf-provreg-dn-defn-00 ietf.org]</ref>
 
[[IAHC]] strongly recommends the [[.us]] [[TLD]] to use the functional SLD.<ref>[http://potaroo.net/ietf/idref/draft-iahc-gtldspec/ potaroo.net]</ref>
 
==Valid Domain Names and SLDs==
In order to register a domain name, the following features must be met:
* It may not contain more than 67 characters, including the domain name extension (such as .com).  
* It must use valid characters, which are those between 0-9, letters a-z and dashes, but the dash "-" cannot be used at the beginning or at the end of a domain name.<ref>[http://www.build-your-website.co.uk/choosing-domain-name-second-level.htm Choosing the right Domain Name]</ref>


==IDN==
An example of this would be .co.uk, where .uk is the (cc)TLD and .co is the (cc)SLD. In this circumstance, the domain name ("example" in "example.co.uk") would be considered the third level domain, as it is in the third position.<ref>[http://www.igoldrush.com/reference/domain-glossary/c/ccsld-country-code-second-level-domain iGoldrush Domain Glossary]</ref> This can become confusing, as the domain name is commonly equated with the second level domain, and the [[subdomain]] is commonly equated with the third level domain. In these circumstances, the third level domain is sometimes referred to as a '''functional SLD'''.<ref>[http://tools.ietf.org/html/draft-ietf-provreg-dn-defn-00 Domain Name and Related Definitions, ietf.org]</ref>
By means of the [[IDN]] system, the valid set of characters has been expanded to include names and words written in native scripts; in this way, the domain names can contain letters from non-ASCII scripts. The [[IDN]] fast track system was approved by [[ICANN]] in 2009, and was adopted by many registries that provide domain space.<ref>[http://www.icann.org/en/topics/idn/ ICANN and IDNA]</ref>


==References==
==References==

Latest revision as of 15:58, 7 January 2022

The Second Level Domain, or SLD, is the data directly before the top-level domain (TLD).[1] For example, in www.example.com, “example” represents the second level domain, as the suffix "(dot)-com" represents the TLD. The SLD is generally the portion of the URL that identifies the website's domain name.[2] Usually, the SLD is determined and defined upon registration of a domain name. More than one SLD can function on the same IP Address.[3]

The DNS is composed of a tree-like hierarchy. Each TLD includes many second-level domains (such as "example" in "www.example.com"); each second-level domain can include a number of third-level domains ("www" in "www.example.com"), and so on.

2LDs[edit | edit source]

ccSLDs[edit | edit source]

Some countries restrict the second level under their ccTLD. These countries require that the second-level domain be one of several pre-determined second-level domains, generally indicating what type of individual or organization may register under that SLD. For these countries, you are not permitted to register domain names under the top level domain. It must be registered under one of the pre-determined second-level domains, called a ccSLD, or Country Code Second Level Domain.[4]

An example of this would be .co.uk, where .uk is the (cc)TLD and .co is the (cc)SLD. In this circumstance, the domain name ("example" in "example.co.uk") would be considered the third level domain, as it is in the third position.[5] This can become confusing, as the domain name is commonly equated with the second level domain, and the subdomain is commonly equated with the third level domain. In these circumstances, the third level domain is sometimes referred to as a functional SLD.[6]

References[edit | edit source]