Each network device working in the computer network and using its resources has its own, unique IP number. It is like with the phone numbers. If the subscriber A wants to talk to her friend B she chooses unique in the world (naturally taking into account the dialling code) phone number. The talk wouldn't be possible if the phone numbers weren't unique. Likewise is in the computer networks. The IP number making the address of a network device is the basic configuration parameter. It serves the communication between devices.
IP number consists of 4 segments separated with commas. The IP address numbers are from the range 0 to 255.
Sample IP address looks like this: 194.146.216.16
Due to the fact that the amount of network devices in the Internet increases very quickly there began the problem of limited amount of IP numbers in the network. At first a method was created to make the computer networks with Internet access use a certain mechanism enabling to limit the amount of IP numbers to minimum. This mechanism was called masquerading or NAT. It works as extensions in telephone exchange. The numbers in the internal network are unique only and exclusively in that network. They are not unique in the whole Internet. To contact with such private number we have first to choose the public number and then private number (in the phone network the subscriber's extension). It causes that a large network including in its range even thousands of network devices can be seen outside in the Internet as just one IP number.
This solution at the beginning brought the possibility of saving numeration, and on the other hand caused some limitations in using P2P programs (peer to peer). The problem consists in that the person having at his/her disposal the internal number can not connect to the other person with internal connection as well (private number). Possible are only the connections of public numbers with public numbers and private numbers with public numbers.
