In large networks, you need your own addressing system, independent of the addressing methods in individual networks (subnets) and allows you to uniquely identify any node (interface, network adapter, host) of the entire network. This system is satisfied by IP addressing. Any IP address has a length of 32 bits, divided into two parts:

• The high-order bits identify the network, i.e. determine the network number. This part is called a prefix;

low bits define the node number. They are called host-part.

The maximum number of distinguishable IP addresses is 232 or 4 294 967 296. One of the main tasks in building an IP addressing system is to split the address space between networks and nodes. Let's look at some ways to solve it.

To separate the composite network into networks and nodes, the classes A, B, C and D are introduced (Figure 9.14) with a fixed number of network numbers. Classes differ in the number of digits allocated to identify networks. For example, for the class A , seven digits are allocated, so the number of networks should not exceed 27 = 128, and the number of nodes in the network - 2 24 " 64 million Since addresses can not consist of only zeros or ones and, in addition, some categories are assigned for official purposes, in real conditions the maximum number of networks and nodes is of less importance (Table 9.3). Fig. 9.14. IP address format

Table 9.3

 Class Identifier Network number range Number Networks Number of nodes class Networks (prefix) A 0 4th byte 1.0.0.0 - 126.0.0.0 126 16,777,216 In 10 3-, 4th 128.0.0 .- 191.255.0.0 16,384 65,535 C 110 2-, 3-, 4-th bytes 192. 0.0.0- 223.255.255.0 2 097 152 254 D 1110 - 224. 0.0.0- 247.255.255.255 - -

IP-a∂peca presentation forms (Figure 9.15). The address can be represented in binary or in hexadecimal form. However, the most common form of representing an IP address is a record in the form of four decimal numbers separated by periods. Each decimal number reflects a byte and corresponds to its value.

Class Features (Figure 9.14 and Table 9.3). To identify the class, the most significant bits of the address are used, and for identifying the network, the higher bytes are used. The one shown in Fig. 9.15 the address belongs to the class B (identifier 10), has a network number of 32 778 (128.10) and a node number of 542 (2.30). In Table. 9.3 for each class, in addition to the identifiers, the range of network numbers and the maximum number of networks and nodes are given. These data indicate that the network:

• Class A refer to large networks, since the maximum number of nodes of each network with a small number of them (126) is over 16 million. To date, the addresses of networks of class A are occupied by large corporations, training centers and other organizations;

• Class C, containing a small number of nodes, should be attributed to small networks; addresses of this class are allocated to Internet providers;

• class B occupy the middle position. Fig. 9.15. Forms of recording an IP address