About domains and DNS

About domains and DNS

Every device connected to the Internet has its own unique identifier, known as IP address.

• Example of an IP address using the older protocol 217.31.201.43

• Example of an IP address using the newer protocol 2001:200:8002:203:47ff:fea5:308

Addresses created in this way are very difficult for people to remember. The Domain Name System (DNS) allows a specific symbolic name known as a domain name to be assigned to a numerical IP address.

Domain hierarchy

To expand the space available for creating domain names, a hierarchy was established. The individual levels are separated by a dot and are numbered in descending order. For example, the domain mail.nic.cz has three levels:

Name Server

Information about domain names is stored on name servers known as NSSETs.

A name server either contains the information needed to resolve a domain name directly, or it refers the query to another name server responsible for the next level in the DNS hierarchy. This referral is known as delegation.

IP Address Lookup Process

Let's consider a user opening the website www.nic.cz in their web browser. The user's computer sends a query for the name www.nic.cz to a local DNS server, which then follows the process shown below:

1. The local DNS server queries one of the root servers for the name www.nic.cz.

2. It does not know the answer, but since it knows where the .cz domain is delegated, it returns a list of name servers for the .cz domain.

3. The local DNS server uses the information provided by the root server and queries one of these servers for the name www.nic.cz.

4. Again, the server does not know the answer, but since it contains information about all subdomains of .cz, it returns information about which server is responsible for the nic.cz domain.

5. The local DNS server then proceeds by querying one of the servers responsible for the nic.cz domain for the name www.nic.cz.

6. The queried server contains information about all subdomains of nic.cz, so it knows www.nic.cz and returns the answer that the name www.nic.cz corresponds to the IP address 217.31.201.43.

7. The local DNS server then returns this address to the user's computer. The computer subsequently connects to the web server at the corresponding address, downloads the page content, and displays it to the user.

Domain Registry

Each domain registry has an organization or individual responsible for its administration and for defining the rules for registering domain names within its subdomains. Administrators of all national Top Level Domains (TLDs) can be found in the list of countries on the website IANA .

General Rules for Domain Registration

• the number and types of characters allowed in a domain name

• who is eligible to register a domain name

• the registration process and registration fees

You can learn more about the registration rules for .cz domain names in the section of Rules and Policies .

Domain registry organizations

CENTR – Council of European National Top-Level Domain Registries, the European association of ccTLD registries. It brings together administrators of European country-code domains such as .cz, .de, .fr, and .sk. In addition to registries from more than forty countries in the region, its members also include registries from outside Europe, such as Japan, New Zealand, and Canada.

AFTLD – Africa Top Level Domains Organization, an organization representing African ccTLD registries.

APTLD – Asia Pacific Top Level Domain Association, an association of ccTLD registries from the Asia-Pacific region.

LACTLD – Latin American and Caribbean ccTLD Association, an organization representing ccTLD registries from Latin America and the Caribbean.