Networks

Introduction

This page will help you navigate through articles about computer networks.

A network is a group of computers or other devices connected by wires or radio waves.

A host is a single device on a network.

The host can be accessed over the network.

A host can send requests to one or more hosts on the network.

A special term has been coined for contacting yourself over the network - contacting localhost

The basis of data exchange over the network is the transmission of electrical impulses. They can be converted to numbers. For example, take a high voltage for 1 and a low voltage for 0.

You can agree on which sets of ones and zeros you need to send for a successful exchange of information.

This will be called a protocol. There can be many protons and they can be embedded with each other. Examples of TCP, IP, UPD

Example of protocol

In this section, you can see my attempt to explain what protocols are to those who have no way of imagining them.

Let's have hosts A and B.

They agreed that to start the work, one should send the other.

11110000

get back

11110001

Before each message with data must be attributed before special counterwhich is first equal

10101010

And with each new message increase counter 1

In front of real data, you should always insert

00000000

Which are not yet in use.

Upon successful receipt, only the increased counter

When all data should be sent

00001111

Data can be transmitted at 8 bits per message.

Example of data exchange on this protocol

Suppose A wants to send B the following data:

1111111100000000

Since data is 16 bits, it needs to be broken down into two messages of 8 bits.

A → B: And sends. 11110000 Waiting back 11110001.

B receives an offer to exchange data, he is ready to receive and sends back 11110001

A receives a ready-to-receive signal from B and sends real data to 11111111. 1010101000000000

B gets B. 101010100000000011111111 and send it back. 10101011

A receives a data acceptance confirmation from B and sends a second piece of data. 101011000000000000000000

B gets B. 101011000000000000000000 and backs up. 10101101

A receives a confirmation of receiving the second piece of data and sends a message about the end of the data exchange. 00001111

B understands that the data has run out and starts processing it.

This example simply shows how protocols work, and in reality they are far more complex. You need to include a check. Package delivery, line checks, and more.

One protocol can be embedded in another.

Let’s say that in our example there are new rules called P1 and P2.

P1: If the data is not available

00000000

And

00000001

The data will not be 8 bits but 16 and in front of them there will be another 8 bits of information in which it is encrypted which program should process them.

P2: If not

00000000

Comes.

10000000

The data will be 32 bits without any other changes.

Obviously, P1 and P2 need to be processed differently. Both are based on our original protocol.

This example is too primitive, but one can imagine that P1 and P2 are new protocols only at a higher level.

IP

IP is the third layer protocol in the OSI model.

Example IP address 8.8.8. 8.

It divides the dots into four parts - an octet of 8 bits. Each octet can range from 0 to 255.

203.0.113.10/24

203.0.113 This is called the Network Portion.

.10 - This is Host Portion.

/24 Subnet Mask or simply netmask is a subnet mask.

With help. mask You can increase the size of the Host Portion using the Network Portion.

Without a mask, IP is not self-sufficient.example)

It was used until 1995. Classful Addressing

After 1995, Classless Addressing

Subnet Mask

In our first example, 24 bits are allocated for the network part of the address and 8 bits for hosts (hosts, also use the term nodes). Figure it out. How this division occurs can be studied Subnet Mask (or just netmask) is a subnet mask.

The mask is also broken into octets. In the table conveniently located binary IP Address and binary mask.

If the address bit is above 0 mask, it corresponds to the Host Portion.

If the address bit is above 1 mask, it is Network Portion.

The smaller the mask, the more unique hosts can be on the network.

In a large local network, you don’t want to spend 24 bits on the network and leave only 8 bits on the hosts.

Let me remind you that 8 bits is only 256 unique variants of which the first .0 is reserved for address of the network itself Network Address ) and the last .255 is reserved for the broadcast address ( Broadcast Address ), which you will learn about below, so there are only 254 unique IPs for hosts. ? Host Address ).

To increase the number of unique addresses for hosts need a different mask. For example,

It is not necessary to distinguish between Host Portion and Network Portion at the octet boundary.

IP from the previous example 10.0.0.10 can be a host on the network with a mask 255.0.0.0 and a mask 255.255.240.0

Let's see where the difference is.

Consider two IP addresses: 10.0.15.10 and 10.0.16.10.

If the mask is 255.0.0. 0

Network part addresses occupy only the first octet and are marked in bold, 10.0.15.10 and 10.0.16.10 are two neighboring hosts on the same subnet.

Consider the same addresses but with a mask of 255.255.240.0

Notice the third octet. Especially on the binary record.

None of the positive bits of 10.0.15.10 hit the network. (no fatty units)

Thus, at 10.0.15.10, the host address remained the same, but the network part of the IP address grew noticeably.

At 10.0.16.10, the unit in the third octet hit the network part. From the host address there are only 1010 a It is not the same as 10.0.15. 10

Thus, now 10.0.16.10 and 10.0.15.10 are not neighboring hosts of the same subnet. hosts on different subnets.

Classful Addressing

If you’ve ever heard of Class A, Class B, C, D, or E IP, that’s the case. Older Class Addressing (Classful Addressing)

A, B, and C are called Unicasts. These are the addresses currently used on the public Internet (with the exception of n private addresses . Principle - one device communicates with one device

D is multicast. One device communicates with several devices. Not supported on the Internet, but supported in large private networks for broadcasting meetings, etc.

Class A: The first 8 bits are always the network part

Class B: The first 16 bits are always the network part

Class C: The first 24 bits are always the network part

Class D: All 32 bits are always the network part

Types of IP addresses

According to the value of Host Portion, addresses can be divided into three types.

• Network Address
• Broadcast Address
• Host Address

Network Address

Network Address or Network Prefix is a unique identifier for a group of devices. Like, like, The street name is a unique identifier for all houses on this street, but is not unique to the street. house (if there is more than one house on the street)

All bits in the Host Portion are 0.

Broadcast Address

Broadcast Address: An identifier that identifies all devices on the network.

Broadcast address all bits in Host Portion are 1

What is different I will explain on the example: the postman was instructed to take the letter to the office TopBicycle On the street Partner and gave instructions

Deliver to the company Company;Site;Type;Address TopBicycle;www.TopBicycle.ru;Partnerskaya Street

It's like a network ader. There may be many offices on the street. Where exactly to carry the letter Do not immediately understand - you need to specify the address of the house (in the case of a network - the host address).

The next day, the postman was instructed to carry the notification of repairs on the street to all houses and offices on the street Partner.

The alerts are the same for all companies.

Deliver to all recipients Company;Site;Type;Address URN.SU;https://www.urn.su;IT;Partnerskaya Street HeiHei.ru;https://heihei.ru;TravelPartnerskaya Street TopBicycle.ru;https://topbicycle.ru;BicyclesPartnerskaya Street Aviasales;https://aviasales.ru;Travel;Partners Street Booking.com;https://booking.com;Hotels;Partners Street Hotellook;https://Hotellook.com;Hotels;Partners Street Velodrive;https://velodrive.ru;Bicycles;Partners Street Xiaomi;https://mi-shop.com;Android;Partners Street Samsung;https://www.samsungstore.ru;Android;Partners Street ;https://.ru;Books;Partners Street GeekBrains;https://gb.ru;Education;Partners Street Netology;https://netology.ru;Education;Partners Street TestSetup.ru;https://TestSetup.ru.ru;Education;Partners Street Pluralsight;https://Pluralsight.com;Education;Partners Street SovcomInsurance;https://sovcomins.ru;Insurance;Partners Street Polis 812;https://polis812.ru;Insurance;Partners Street Vivo;https://ru.vivo.com/;Android;Partners Street Beget;https://beget.com;Hosting;Partners Street Reg.ru;https://Reg.ru.ru;Hosting;Partners Street OLDI;https://oldi.ru;Laptops;Partners Street

It's the equivalent of a broadcast address. If there were two offices on the street, you should carry letters both ways. If twenty, all twenty. You don't have to know who's in what house, so if he's walking down the street with letters, It is easy to enter all houses in order (not according to the list, but because they are located on the street).

Host Address

Host Address: An identifier that identifies a particular device on the network.

A host address can have any combination of bits in a Host Portion except two: only zeros and only one.

Only zeros are a network address, only a few are broadcast. Everything else is host addresses.

The network address in the decimal record may not end at 0

Consider 10.128.224.64 with 255.255.255 mask. 224.

Checking if the address is a network address means checking whether the Host Portion contains only units or not.

One IP address is not enough for this, you need to consider it together with the mask to understand what it is. Host Portion

The network part is highlighted in bold, it is obvious that only zeros remain in the host part and this address is the network.

CIDR Notation

Consider the mask 255.255.255. 0

The first 24 bits are units. Do not write constantly 255.255.255

/24

Next format is first slash, then Network Portion length

For example:

203.0.113.10/24

Private

There are three ranges of addresses that are not used on the public Internet.

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16

It is recommended to avoid using the address 169.254.0.0/16. APIPA

127.0.0.1 is reserved for Loopback Address

This means the address of your computer. You can tell me your home address.

In IPv6, it looks like ::1

Subnetting Networks

Consider the IP address. 10.0.0.0/8

10.0.0.0
255.0.0.0

Range of host addresses (not including ends):

10.0.0.0 - 10.255.255.255

N 00001010 00000000 00000000 00000000
B 00001010 11111111 11111111 11111111
M 11111111 00000000 00000000 00000000

RFC

HTTP

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Article author: Andrei Olegovich