Domain (Internet)

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Schematic representation of the DNS hierarchy

A domain (from English domain [ də (ʊ) ˈmeɪn ] 'area', 'domain') is a coherent part of the hierarchical Domain Name System (DNS). In the domain allocation process , it is a globally unique and unambiguous name under a top-level domain that can be freely selected under certain rules . The registration office (NIC = Network Information Center ) of the respective top-level domain defines the exact rules for assigning names . Further subdomains can be added to a domain, each separated by a point. Each section (domain and subdomain) can contain a maximum of 63 characters. However, the total length of the fully qualified domain name (FQDN = Fully Qualified Domain Name) must not exceed 255 characters. With each FQDN formed in this way, any physical or virtual object can be uniquely addressed worldwide. The connection between the FQDN and the actual location of the object is established via entries in name servers , which ultimately refer to the IP address of a server .

The DNS namespace

Structure and rules

The DNS namespace is represented as a root tree . Each node in this tree has a name that is not unique without specifying a full name. Thus, for example, node Example not clearly determine, because this name to one under and the other under could be assigned.

Each domain name therefore consists of several name parts (labels), which are separated from one another by periods.

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

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


        (root) Label der 0. Ebene, Null-Label
         /  \
        /    \
      com    org Labels der 1. Ebene, Top-Level-Domains (TLD)
      /        \
     /          \
 example      example Labels der 2. Ebene, Second-Level-Domains
    |         /  |  \                 und Hostnamen direkt unter einer TLD
   www       de  en www Labels der 3. Ebene, Third-Level-Domains
            /\                         und Hostnamen unter Second-Level-Domains
         foo bar
(beliebig erweiterbar)

Fully Qualified Domain Name (FQDN)

The full name of a domain is known as the Fully Qualified Domain Name (FQDN). In this case, the domain name is an absolute address .

The FQDN results from: 3rd level label. 2nd level label. Top-level domain. root label

and reads with it

Since the root label is always empty (it is an empty string), will in most user applications (such as browsers) generally to the input of the point between the label of Top Level Domain and the root-label waived . Strictly speaking, this notation is no longer an absolute, but a relative address and thus no longer an FQDN. When specifying in resource records on name servers , the full name with a period must be specified.

The term Fully-Qualified Host Name (FQHN) is used as a generic term for FQDN and IP address in some RFCs .


Layout and function

A subdomain is a domain that is below another in the hierarchy. In common parlance, this usually means domains in the third or a further level. A domain that is directly below the top-level domain is colloquially -not- referred to as a subdomain, but as a second-level domain or just a domain.

As an example, consider the top-level domains comand org. The second-level domains example.comor are example.orglocated under these domains . Each subdomain is an independent domain in which other domains and host names can be located. For example, example.orga second-level domain is the top-level domain orgor de.example.orga subdomain of

In some top-level domains there is a restriction on the second-level domains: As were formerly ukas only a handful of domains,, co.uksettled. Universities were given third-level domains under, government agencies under, commercial companies under A mixed system is used in Austria: second-level domains under atare freely assigned, under ac.atonly universities and under gv.atonly authorities receive a third-level domain.

Traditionally, sub-domains are used for the logical and physical separation of services within the domain of an organization, e.g. B. used www.beispiel.atfor the web server or mail.beispiel.atfor the mail server. But this is just a convention ; a web server can just as well be operated on a computer with the domain name web.beispiel.ator

Conventional names for different services:

  • Web server: www.
  • Web server especially for mobile devices: m.
  • 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, for independent websites, language versions or to route e-mails to branches with their own mail server.

Creating a subdomain for this purpose only makes sense if the resulting domain names use different target pages or servers, for example and

On the other hand, you can also create subdomains in order to redirect to certain departments and areas within a company or organization. Examples of a subdomain for forwarding to individual areas or locations of a company and / or organization:

Since you can define redirects, you can redirect or forward to certain areas of the existing domain with the subdomain. By setting up additional subdomains, you can possibly increase the number of visitors to the site.

Distributed administration with subdomains

Like any other domain, a subdomain can be administered on any name server . So could z. B. can be managed on a name server in Germany, while is located in the USA (see DNS delegation ).

Some service providers use this option and offer third-level subdomains with forwarding to a longer URI . This has the advantage for the provider that they can set up these themselves differently than with second-level domains and thus only incur minimal costs. Popular subdomains for German sites are subdomains . de . TLD with different top-level domains.

special cases

Some countries, for example Turkey or Australia , only assign third-level domains . Registration of [example].tror is [example].aunot possible, domains such as [example] are offered instead . See also: top-level domain

The domain names , and were reserved by the IANA so that they can be used in your own documentation and test environments. The purpose of this reservation is to avoid conflicts with real existing domain names. The top-level domains .test , .example , .invalid and .localhost were also reserved for this purpose . All reserved names are defined in RFC 2606 .


Legal nature

The legal nature of domains was controversial, but in the past ten years, judgments by the Federal Constitutional Court , the Federal Court of Justice (domain attachment), the Federal Fiscal Court (tax deductibility) and the European Court of Human Rights (ECHR ) have clarified these: A domain owner has a contractual right against the registry DENIC eG to use the domain. This is protected by the property guarantee ( Art. 14 Basic Law) and can be attached . He is not an absolute , i.e. H. towards everyone, protected right.

The dispute can be summarized as follows: According to one opinion, the domain address is a right of its own kind ( sui generis ). This is comparable to property and is a benefit to everyone, i.e. H. absolute , protected property right. This means that the domain address itself can be the subject of the attachment. This view is justified, among other things, by the fact that domain addresses can be "bought, sold, rented and auctioned".

The Federal Constitutional Court and the Federal Supreme Court reject this view. The domain itself is a technical Internet address. The "owner" of a domain does not acquire ownership or any other absolutely protected right to the Internet address. On the one hand, there is a lack of reification, on the other hand, the legislature has not protected the Internet address itself exclusively against everyone. The factual exclusive position based on the fact that the DENIC eG registry, which has a dominant market position, only assigns an Internet address once, does not justify absolute protection in the legal sense. A domain address is therefore not a license. This does not exclude the possibility that absolutely protected trademark or trademark rights of the domain owner or other persons may exist in a character string that forms a domain address. However, regardless of the legal status of the domain owner, this would exist at the (technical) Internet address as the domain address.

The domain owner has a contract with the DENIC eG registry. This entitles him to the DENIC eG registry to use an Internet address and to register as the owner of the Internet address. This registration may have a. the function of identifying him as the owner of the Internet address ( so-called WHOis query ).

According to the Federal Constitutional Court, these contractual rights are covered by the property guarantee in Article 14 of the Basic Law.


According to the case law of the Federal Court of Justice, the contractual claims can be seized as assets within the meaning of the law of enforcement . The object of the seizure is therefore not the Internet addresses themselves, but the contractual rights of use. When a .de domain is seized, DENIC eG is the right third party debtor .

European law

According to European law, it has been clarified that the right of use is property right according to Article 17, Paragraph 1 of the GRC, the Charter of Fundamental Rights of the European Union . This was decided by the European Court of Human Rights (ECHR) with its judgment of September 18, 2007:

The right to use a specific Internet domain acquired through the registration contract with a domain registry represents a protected property position according to Article 1 of the 1st Additional Protocol to the European Convention on Human Rights (ECHR ).

See also


  • Tim Schumacher, Thomas Ernstschneider, Andrea Wiehager: Domain names on the Internet: A guide to naming strategies . 1st edition. Springer, Berlin / Heidelberg 2002, ISBN 3-540-42910-7 , pp. 231 .
  • Jens Bücking, Henrik Angster: Domain law . 2nd Edition. Kohlhammer, 2010, ISBN 3-17-019820-3 , pp. 222 .

Web links

Individual evidence

  2. RFC 2626 ; Section 3.3 RR NAME Considerations
  3. RFC 1035 ; Section 3.1. Name space definitions
  4. RFC 1035 ; Section 4.1.4. Message compression
  6. a b c d e BVerfG, decision of November 24, 2004 , Az. 1 BvR 1306/02, full text = MMR 2005, 165.
  7. ^ BGH, decision of July 5, 2005 , Az.VII ZB 5/05, full text = MMR 2005, 685.
  8. a b c d e f BGH, decision of 05.07.2005 - VII ZB 5/05 - openJur. Retrieved November 9, 2019 .
  9. BFH, judgment of October 19, 2006 , Az. III R 6/05, full text = BFH MMR 2007, 310.
  10. ECHR judgment of September 18, 2007, Az. 25379/04, 21688/05, 21722/05, 21770/05 - (PDF; 46 kB)
  11. LG Eating Decision of 22.09.1999: 11 T 370/99 . WebDok 49/2000, doi : 10.7328 / jurpcb / 200015112 ( [accessed on November 9, 2019]).
  12. BGH, judgment of 11.10.2018 - VII ZR 288/17 - openJur. Retrieved November 9, 2019 .
  13. a b BGH, judgment of 11.10.2018 - VII ZR 288/17 - openJur. Retrieved November 9, 2019 .
  14. Federal Supreme Court (finally) creates legal security for domain attachments. In: December 18, 2018, accessed on November 7, 2019 (German).
  15. ^ LG Frankfurt a. M., judgment of May 9, 2011 , Az. 2-01 S 309/10, full text.
  16. HUDOC - European Court of Human Rights. Retrieved November 9, 2019 .