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IP address in detail

From Wikipedia, the free encyclopedia
IP-address (IP address, short for English. Internet Protocol Address) – a unique identifier (address) for a device (usually a computer) connected to a local network or the Internet.
An IP address is a 32-bit (IPv4) or 128-bit (IPv6) binary number. A convenient form for recording an IP address (IPv4) is to record in the form of four decimal numbers (from 0 to 255), separated by periods, for example, 192.168.0.1. (or 128.10.2.30 is the traditional decimal form for representing the address, and 10000000 00001010 00000010 00011110 is the binary form for representing the same address).
IP addresses are the main type of address based on which the network layer of the IP protocol transmits packets between networks. The IP address is assigned by the administrator during the configuration of computers and routers.

The IP address consists of two parts: network number and host number. In the case of an isolated network, its address can be selected by the administrator from the address blocks specially reserved for such networks (192.168.0.0/16, 172.16.0.0/12 or 10.0.0.0/8). If the network should work as an integral part of the Internet, then the network address is issued by the provider or the regional Internet registrar (Regional Internet Registry, RIR). There are five RIRs in total: ARIN serving North America; APNIC serving Southeast Asian countries; AfriNIC serving countries in Africa; LACNIC serving South America and the Caribbean; and RIPE NCC serving Europe, Central Asia, and the Middle East. Regional registrars obtain autonomous system numbers and large address blocks from ICANN, and then issue autonomous system numbers and smaller address blocks to local Internet registries (LIRs), which are usually large providers.

The host number in IP is assigned regardless of the local host address. By definition, a router enters several networks at once. Therefore, each port on the router has its own IP address. An end node can also be a member of several IP networks. In this case, the computer must have several IP addresses, according to the number of network connections. Thus, the IP address characterizes not a single computer or router, but one network connection.

IP Classes
Which part of the address refers to the network number, and which part to the node number, is determined by the values ​​of the first bits of the address. The values ​​of these bits are also indications of which class an IP address belongs to.
The figure shows the structure of the IP address of different classes.

structure of the IP address of different classes

Classless Addressing
Since the second half of the 90s of the XX century, class routing has been universally replaced by classless routing, in which the number of addresses on the network is determined solely and exclusively by the subnet mask.
Special IP Addresses
There are several conventions in the IP protocol for the special interpretation of IP addresses:
if the entire IP address consists only of binary zeros, then it denotes the address of the node that generated this packet; This mode is used only in some ICMP messages.
if the network number field contains only zeros, then by default it is considered that the destination node belongs to the same network as the node that sent the packet;
if all the bits of the IP address are 1, then a packet with this destination address should be sent to all nodes located on the same network as the source of this packet. Such a distribution is called limited broadcast;
If there are only units in the destination node number field, a packet with such an address is sent to all network nodes with the specified network number. For example, on a network 192.190.21.0 with a mask of 255.255.255.0, a packet with the address 192.190.21.255 is delivered to all network nodes of this network. Such a distribution is called a broadcast message.
Dynamic IP Addresses
An IP address is called dynamic if it is assigned automatically when the device is connected to the network and is used for a limited period of time, usually until the end of the connection session.

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