An IP address (IP is short for Internet Protocol) is a 32-bit number, usually written as four 8-bit numbers separated by periods. Since decimal notation is used in practice, the number in each of the four fields can take a value from 0 to 255, for example: 192.152.22.10.
The individual parts of the IP address correspond, roughly speaking, to successively smaller networks that we encounter "on the way" to the computer we are interested in. For example, in the address 149.156.24.12 the first number - 149 - means Poland (one of several numbers assigned to our country), 149.156 is Krakow (more precisely - the Krakow city network, MAN), 149.156.24 refers to a specific institution connected to this network, and the last part of the address is already the number of the computer within this instance.
In the original version of the IP protocol (designed for ARPANet), the highest 8 bits of addresses identify the network, while the remaining 24 bits represent the device connected to the network. Since ARPANet was to connect at most several dozen institutions, the adopted 32-bit address space seemed to be a modern and future-proof solution. Since it soon turned out that ARPANet would connect more than 256 networks, five classes of 32-bit addresses were distinguished for networks of various sizes. Among them, classes A, B and C are widely used:
? Class A. Intended for wide area networks with many addressable devices. The part identifying the network consists of one (first) byte, the other three bytes describe a specific computer. It is therefore possible to address 16 million devices in each of the 127 networks. This class includes addresses from 0.0.0.0 to 126.255.255.255 (of which addresses from 10.0.0.0 to 10.255.255.255 are reserved for special purposes).
? Class B. Intended for medium-sized networks. The parts identifying the network and individual computers are of equal size and consist of two bytes. It allows to address 65,000 devices in each of 16,000 networks. The class includes addresses from 128.0.0.0 to 191.255.255.255 (minus reserved addresses from 172.16.0.0 to 172.31.255.255).
? Class C. Most common on the Internet, designed for small networks of up to 254 computers. The part identifying the network is the first three bytes, individual computers are identified by the last byte. Up to 2 million different Internet subnets can have an address of this class. The pool of available addresses ranges from 192.0.0.0 to 223.255.255.255 (addresses from 192.168.0.0 to 192.168.255.255 are reserved).
The other two classes (D and E) are of marginal importance:
? Class D. Intended for multicast addresses. Includes addresses from 224.0.0.0 to 239.255.255.255.
? Class E. Reserved for future use. Includes addresses 240.0.0.0 and above. Addresses 127.xxx are reserved for special purposes (so-called loopback, used for internal tests of the local computer).
IP addresses, due to their obscure nature, are rarely used in practice. Most computers are assigned domain names that are much easier for humans to remember. DNS servers handle the conversion between these two addressing methods.
