The principles of computer networks 2

Computer Network

10.6.1.2 explain the purpose and representation of the IP address;
10.6.1.3. Explain the purpose of the domain name system (DNS);

IP-address - is the main type of addresses on the basis of which the network layer transmits packets between networks. These addresses consist of 4 bytes. They are assigned by the administrator during the configuration of the computers and the router. It consists of two parts:
a) Network number — chosen by the administrator arbitrarily or assigned by the InterNic service;
b) Node number in the network - assigned independently of the local node address.

IP address. In order for the computers to find each other in the information exchange process, there is a single addressing system on the Internet based on the use of an IP address.
Each computer connected to the Internet has its own unique 32-bit (in binary) IP address, which uniquely identifies the computer.

For software and hardware devices, an IP address is just an integer to store which is allocated exactly 4 bytes of memory. Those. a number in the range from 0 to 4294967295. It is difficult for a person to memorize such bulky numbers. Therefore, for clarity, the IP address is recorded as a sequence of four numbers separated by dots in the range from 0.0.0.0 to 255.255.255.255. Each of these four numbers corresponds to the value of each byte of the four, in which the whole number is stored.

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The IP address contains the network address and the address of the computer on the network (network address and subnet address)

To ensure maximum flexibility in the process of distributing IP addresses, depending on the number of computers on the network, the addresses are divided into classes A, B, C, D, E.
The first bits of the address are allocated to identify the class, and the rest are divided into the network address and the address of the computer on the network.

7

0..255

0..255

0..255

0..255

network number + computer number in the network

Askar wrote down the school server’s IP address on a piece of paper and put it in his jacket pocket. Askar’s mom accidentally washed the jacket along with a note. After washing, Askar found four fragments in his pocket with fragments of an IP address. These fragments are labeled A, B, C, and G. Recover the IP address. In the answer, indicate the sequence of letters denoting fragments in the order corresponding to the IP address.

Decision:
the most important thing is to remember that each of the 4 numbers in the IP address must be in the range from 0 to 255
therefore, we immediately determine that fragment A is the most recent, because otherwise one of the numbers is greater than 255 (643 or 6420)
G fragment (number 20) can only be the first, since variants 3.1320 and 3.13320 give a number greater than 255
of fragments B and C first must be B, otherwise we get 3.1333.13 (1333> 255)
thus, the correct answer is GBVA.

DNS (Domain Name System) – domain name system
A domain is a set of hosts joined into a logical group.
DNS is a distributed database that supports a hierarchical name system and is designed to determine the IP address by a known symbolic host name (and Vice versa).
one.example.com – relative domain name
one.example.com ahhh! – absolute domain name
. – root domain
com. – first (top) level domain
example.com ahhh! – second level domain
one.example.com ahhh! – third-level domain 2

DNS (Domain Name System) – domain name system
DNS converts the digital IP address of the host (computer) into a character set. Domain - a group of network resources that has its own name and is managed by its network station.
The address of a resource of the world wide web, recorded in the DNS standard, is divided into several components, separated from each other by a point. These elements are called "domains". This designation is called URL (Uniform Resource Locator), which can be translated into Russian as "universal resource locator".

Internet Network Information Center (InterNIC) - Information center of the Internet (international network information center) - an organization dealing with the formation, registration and strategic development of the Internet, including the registration of domain names.

Distributed DNS database
First level:
generic name:
com – commercial organizations
edu – educational institutions
gov – governmental organizations
org – non-profit organizations
net – the organization that supports network 

State domains:
Kz – Kazakhstan
ru – Russia
am – Armenia
at – Austria
tv – Tuvalu
io – British Indian ocean territory
me – Montenegro

The working principle of DNS:
To find the desired computer on the Internet custom machines help DNS servers, which are programs that are accessed to seek out the correct IP address for the URL.

DNS work is quite simple, but because of ignorance of its basics, there are a lot of problems and questions when transferring an existing domain name and registering a new one.
Let's stop a little more detail on the description of the scheme.
When a user launches a web browser and enters the domain name of the site, his PC sends a request to the ISP's DNS server to obtain the IP address of the domain (1).
If the provider's DNS servers do not find information about the requested site in their cache, they send a request to the root DNS servers (2).
The root DNS server searches its database for information about the name servers of the hosting provider on which this site is present. Next, it reports them to the provider's caching DNS server (3).
After the caching DNS server of the Internet provider receives information about the name servers of the hosting provider, it polls any of them (4) and, in the case of a positive result of obtaining an IP address (5), places it in the cache.
Caching is used to reduce both the load on Internet channels and to speed up the result of the request. The provider's DNS server then passes the IP address to the user's browser that made the site request (6).
And after that, the browser, having received the IP-address of the requested site, goes to the site itself (7 and 8).
It is important that the update of information about the provider name server is not instantaneous, but after a certain time (for each DNS server, depending on the settings and provider, these values may vary).