The hierarchical system of domains on the Internet solves the main problems – it enables the systematic assignment of names and the delegation of the administration of the entire system. Each node of the domain name hierarchy is managed by a specific entity (organizations, associations, etc., in lower levels these are already specific legal and natural persons), which is in charge of administrative and technical matters, ensures the operation of this node and the delegation of administration of some subtrees of this node to other entities.
Based on RFC 2870 – Root Name Server Operational Requirements, the root domain (zero-order domain) is the responsibility of the international organization ICANN (Internet Corporation for Assigned Names and Numbers), which is responsible for DNS namespace, distribution of large blocks of IP addresses, the number management of autonomous systems, etc. It passes the power to manage individual TLDs to other entities, which break them down into SLDs, and they pass them on to further entities, etc. First-order domains are divided into ccTLDs (country code TLDs), which relate to individual countries (e.g. cz for the Czech Republic, sk for Slovakia, pl for Poland, de for Germany,…), or unions (e.g. us – United States, eu – European Union), and gTLDs (generic TLDs), which are not related to states but were originally intended for thematic division (com – commercial sites, org – sites of international organizations, net – sites related to networks, etc.). The designation of domains is not so much observed today, because the market for domains is more or less free. However, the delegation must be firmly maintained and it must always be clear who is responsible for running which domain.
The cz domain, which is intended for the Czech Republic, is under the control of the CZ.NIC organization, which is an interest association of legal entities. Its task is to ensure the administrative and technical side of the operation of this domain. It sets out the rules according to which the second level * .cz domains are given to other entities. This is currently done through so-called accredited registrars, which are commercial entities that are contractual partners of CZ.NIC and which sell second-order domains to end customers (legal or natural persons) and by this sale essentially “delegate” the purchased name. If someone buys the seznam.cz domain in this way, for example, the entire relevant subtree is in the domain hierarchy under their administration and they can use it in its entirety and possibly delegate some subtrees.
A similar model as the .cz domain is used for most other TLDs. It is more or less up to the relevant organization to determine the rules that define who and under what conditions can obtain a domain name under a given TLD.
Each domain name (a node of the hierarchy of this system, i.e. a subtree) is assigned so-called authoritative DNS servers. It is a set of servers that carry the information needed to work with a given domain. They can already contain specific data (i.e. IP addresses, names of mail servers, etc.) and especially the names of other DNS servers that are authoritative for subdomains (i.e. lower-order domains under this domain). The word “authoritative” here means that these are servers that carry binding information about a given domain, and all devices on the Internet should follow them so that they always get the right result when translating a domain name to an IP address through this hierarchy.