What is DNS and how does it work? What is a domain?

IP address

And this title of the article already exists © Google 

As your apartment is in the house, so each site is on the server. Each house has its own address, so the server has an address - it is called IP ( internet protocol ) address . These are the same numbers like “212.80.32.20”. They consist of four numbers (each number is from 0 to 255, that is, the smallest address is 0.0.0.0, the largest is 255.255.255.255), if we multiply 256 * 256 * 256 * 256 = 4294967296, then we will find out the maximum number of addresses . It turns out that there are only a little more than 4 billion of them. It turned out that there are fewer IPs than people, so back in 1996 they came up with a new protocol IPv6 , which (it’s easy to guess from the name) uses 6 numbers and the number of addresses in it will provide the possibility of using more than 300 million IP addresses for every inhabitant of the Earth.

The maximum number in “256” (counting from zero 0-255) was chosen for a reason. The fact is that in computers, numbers are stored in the binary number system , in which the number 0 or 1 is called bit (a unit of information). Every eight bits make up a byte, one byte contains a number from 0 to 255 or 2^8 = 256, where 2 is the number of possible digits in the number system (0, 1), and 8 is the number of digits. Things like that :)

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Domain name

Duplicate Wikipedia © Author's quote 

So, all servers have an address where our favorite and cozy google, netflix, etc. are located. Now imagine a situation in which you have to type 212.80.32.20 in your browser to visit a website. This is very inconvenient, so they came up with giving addresses human names, for example www.digiants.agency . This domain name consists of three parts - “www”, “digiants”, “agency”, which are separated by dots. Each word is a domain, the complete phrase is a domain name. Information about each domain is stored on DNS ( domain name system ) servers. Each individual DNS server is responsible for its own domain. Consider www.digiants.ua:

1. Information about first-level domains (.com, .de, .agency, .ua, etc.) is located on DNS root servers (13 in total), and coordinates first-level domains ICANN . So, the address of the DNS server that serves the “ua” domain is located on the root server.
2. DNS servers that store information about .ua subdomains (digiants.ua, something.ua etc) belong to the company hostmaster . Also, this company keeps a single database of all companies that have the right to register the any-word-here.ua domain, here is the list . These companies are called “domain name registrars”.
3. Information about the domains below the level is with the owners of the domains. For example, you bought digiants.ua - it means you own it, and the DNS servers of the registrar company indicate the IP address of your DNS server, which means you can set IP addresses to any subdomains yourself (www.digiants.ua, somesite.digiants.ua etc ).Below we will consider how to technically transfer a domain to someone.

What does name server do

Natural admin, 
There is only one for the entire subnet: 
Both young and single, 
And 20 years old and with a beard 
© Folklore 

The server supports domains that are delegated to it. That is, it contains information about domains in the format of DNS records. When your browser makes a request to a DNS server, it returns all DNS records (or resource records ).

The main types of resource records:

1. A - stores the IPv4 address of the domain.
2. AAA - stores the IPv6 address of the domain.
3. NS is the address of the DNS server that is responsible for this domain.
4. SOA - stores the domain name and cache time to live (TTL - time to live). Remember you are “linking” a domain to a new hosting and they tell you that it will take from 2 to 48 hours. This is exactly what happens because of this post. After all, in order not to search the Internet for the IP address of the domain every time, the DNS server temporarily remembers (caches) the information.
5. MX - mail server data.
6. TXT - any data (for example, to confirm Google).
7. SRV - host name and port for some services.

That is, summing up the above, the useful information of the response from the DNS server will be: 
A - 212.80.32.20 
NS - … 
MX - … 
...

How does the browser find out the IP address of the domain

Firefox is a great browser , and will forever remain in memory 

© Vertex 

Let's say you wrote in the browser www.digiants.agency . First of all, the browser reads the file hosts (this is a file in which the computer owner himself can write which IP address corresponds to which domain), if he did not find a match there, then he makes a request to the DNS server (later we will consider only recursive query to the DNS server).

When asked, it turns out that this server does not know about this domain. Then it contacts the root server , which answers: I have no information about the domain www.digiants.agency, but there is a record that “agency” has such an ip - 212.80.32.20 (this and below, IP addresses are not are real). Then the server asks 212.80.32.20 - “do you know www.digiants.agency”, he answers - “no, but there is a record that digiants.agency is located at 185.143.145.155“. And in the end, the request is sent to the third DNS server and receives the desired IP address (in this case, the DNS server remembers its path for the time specified in the TTL). As a result, the browser receives the IP it needs.

Interesting facts

Web 1.0 is the state of the Internet when it was not the same. 
© Lurk 

1. The analogy with a house and an apartment is not true, since one IP address (an apartment in a server house) can have many domains, but one domain can contain several IP addresses (for load distribution ).
2. ICANN is not an American, but an independent international organization, you can look at their financial report .
3. The main participants in the Internet governance process are the Internet Design Working Group, the Internet Society, the World Wide Web Consortium (W3C), the Internet Corporation for Assigned Names and Numbers (ICANN). ), states, Internet providers, registrars. In short, thousands of them.
4. There are 13 root servers in total, but there are alternative root servers , and the Internet Architecture Council
5. Recursive queries to the DNS server require more load, so they are usually accepted only from a narrow range of queries (for example, ISPs allow only their clients to make such queries, etc.
6. Historically, each first-level domain has something means, for example, .com (commercial) - for commercial projects, .org (organization) - for non-commercial projects, .net (network) - for network-related companies, etc. You can see the full list here Although these the names have lost their relevance a little.