A domain (including domain ) is a contiguous portion of the hierarchical Domain Name System (DNS).

Each computer has a domain in the DNS on an individual name (eg www ). This individual is called – by a point separated – the name of the domain (eg example.com ) expanded. The so constructed fully qualified domain name (eg www. example.com . ) can be the DNS with IP address to be dissolved, can be used then to network connections to this computer set up (for example, the http://www.example.com/index.html website access). The Fully Qualified Domain Name (and thus also the name of the domain) is often part of URLs .

The DNS name space

Structure and rules

The representation of the DNS name space is a “root tree” . Each node of this tree has a name, without specifying the full name is not unique. Thus, for example, the node example not clearly determined, because this name is the one under example.com and, second, example.net could be assigned.

Each domain name thus consists of several parts of names (labels), separated by dots.

The rightmost name in the hierarchy of the tree root at the highest, the leftmost node name is at the lowest. The highest level in the DNS hierarchy, it has the so-called root domain (or zero or root label called). She has, by definition, an empty node names consisting of a single octet is filled with zeros.

Topologically below and left of the root domain so listed, followed by the name of a top-level domain (TLD). Below or in the name of the next top-level domain names follow the second-level domains, followed by third-level domains , or simply subdomains .

Fully Qualified Domain Name (FQDN)

The full name of a domain is as its Fully Qualified Domain Name FQDN) refers to (. The domain name is in this case, an absolute address .

The FQDN www.example.com. is by itself:

3rd-level label. 2nd-level label. Top-level domain. root-label

and is thus

      www. example. com.

Since the root label is always empty (it is therefore only an empty string), in most user applications (eg browsers) to the entry point between the root-label and label the top level domain in the usually omitted. Strictly speaking, this is not writing this to an absolute but a relative address and thus no longer a FQDN. The indication in resource records on name servers , however, the full name will be given point.

As a generic term for FQDN and IP address in some RFCs the term Fully-Qualified Host Name (FQHN) was used.

Subdomain

Structure and function

As a sub-domain is called a domain, which is in the hierarchy under another. In common usage are therefore usually meant domains in the third or another level. A domain that is located directly below the top-level domain is referred to colloquially as a subdomain not, but as a second-level domain, or only as a domain.

In the above example, there is the top-level domain com. and org. . Among these domains are the sub-or second-level domain example.com. and example.org. located. Each subdomain is independently another domain in the other domains and host names can be. For example, example.org. subdomain of the top-level domain org. or de.example.org. subdomain of example.org. .

The benefit of this system demonstrates the following analogy from everyday life: Peter Müller Peter Müller in Hamburg in order to distinguish Munich, there are zip code and city. At two Peter Mueller to distinguish in Hamburg, there are street and house number (etc.). This function is performed in the Internet domain respectively of their sub-domain (s) .

For logical and physical separation of services within a second-level domain are traditionally third-level domains , such as www.example.com to the web server or mail.example.com the mail server used. The historic designation of the host name www for a Web server does not match any standard and has no meaning. Instead of calling the web server could, for example, web or just the second-level domain without a prefix can be used. The functional designation of host names for Web, mail, Jabber, or FTP server is not specified and can be freely chosen. However, have evolved over time naming some of the different servers in a domain established within:

• Web server: www.
• Mail Server: . mail . smtp pop3. imap.
• FTP Server: ftp.

Advantages of subdomains

Logical structure

The logical structure is used for example for distributed branches or departments of a company to guide for independent web sites, languages ​​or e-mail to branches with their own mail server.

To create a subdomain for this purpose is only useful when using the resulting domain name different target sites or server, for example mail.extern.wikipedia.de and ftp.extern.wikipedia.de.

On the other hand, one can also create sub-domains so as to forward to specific departments and divisions within a company or organization. Examples of a subdomain for distribution to specific areas or locations of a company and / or organization:

bremen . example.com
hamburg . example.com

personnel . example.com
suppliers . example.com

Since you can set redirects, can I transfer the subdomain to certain areas of the existing domain or to. The additional set of subdomains you can also it increased the number of visitors of the site.

Distributed management with subdomains

A subdomain is just like any domain to any name servers are managed. This could for example be administered de.example.com Germany Name servers in one, while example.com in the USA , is (cf. DNS delegation ).

Some service providers use the opportunity and offer third-level subdomains to redirect to a longer URI to. This has the advantage for the providers that they, unlike second-level domains can establish itself and minimal costs incurred by it. Popular subdomains for German sides subdomain . de . TLDs with different top-level domains.

Special cases

Some countries, such as Turkey or the UK , exclusively awarded third-level domains . Thus, a registration of [example] . uk or [example] . tr impossible instead be domains such example]. [co.uk . offered See also: Top-level domain

The domain name example.com , example.net and example.org were from the IANA registered so that they can use documentation and test environments in their own. The purpose of this book is really existing domain names to avoid conflicts. To this end, and top-level domains . test , . example , . invalid and . localhost reserved. All names are reserved in RFC 2606 defined.

Nature of domains

The law of nature. De domains has been consolidated over the past few years by including the Constitutional Court judgments MMR 2005, 165 (adacta.de), BGH MMR 2005, 685 (domain seizure), BFH and MMR 2007, 310 (tax deductible). It is believed that a. De domain is not an absolute right but a contractual claim against the registry DENIC eG, focused on the use of the domain. This is a. Com domain is a legally protected asset, similar to “legitimate possession of a thing” and therefore “property-like”.