In the past few decades, network technologies have been developing rapidly . Since the formation of the global Internet, a huge number of smaller local networks and individual users have been connected to its resources. In this regard, there was an urgent need to describe a clear addressing of all network nodes. A solution has been found.
The TCP / IP model is a four-level structure. Each of these levels is responsible for its functions, but one of the most important tasks is network addressing. For these purposes, use the IP address of the fourth version, which is a number consisting of thirty-two digits. It clearly identifies the network in which a particular host is located, as well as, directly, the host address. Obviously, the number of these addresses is strictly limited.
For proper addressing, the equipment needs to clearly know where in the address the network is indicated, and where is the host. The network mask takes on this mission, which greatly simplifies the work of a large number of different network equipment, both passive and active.
The network mask clearly defines how many bits are related to the network address, and which one to the host address. This technology allows you to significantly increase the volume of possible addresses, in comparison with the technology of clearly dividing subnets into classes. It also allows you to avoid any conflict situations that arise in the case of finding the same address.
The network mask allows you to divide large networks into smaller ones, which are divided, in turn, into even smaller ones, and so on, until thirty digits pass. But as the number of networks increases, the number of hosts decreases. Therefore, applying this technology, you must very carefully consider the number of addresses you need for hosts.
As a rule, the mask is set with a number from nine to thirty. This number means the number of characters in the binary address code , which is responsible for the network address. So, for example, for the address 193.29.204.19, if it has a network mask of 24, the network address will be 193.29.204.0, and the addresses of the hosts will be 193.29.204.1-254 (since the address 193.29.204.255 is broadcast).
In order to determine all this, it is necessary to calculate the subnet mask according to certain rules. In the above example, this process was as follows. So, first you need to translate the address into a binary system . But you need to do this in such a way that you get four octets. Missing digits must be replaced with zeros before the number. Further, the given net mask, or rather its number, is written in the form of successive units in the quantity corresponding to this number. It is more convenient to do this clearly under the address itself, digit by digit. Next, we mark at the address with a dash the moment when the units end on the mask and begin zeros. And we get: on the left is the subnet address, on the right is the host address. We translate back to a more familiar decimal form. That's all.
This task is not at all difficult, but very useful when building large-scale branched networks. A network mask can be a reliable helper for building a clear hierarchical and orderly structure.