In the past few decades, actively developing network technologies.Since the formation of the global Internet resources was connected to its huge number of smaller local networks and individual users.In this regard, there was an urgent need for clear description of the addressing of nodes on the network.The solution was found.
Model TCP / IP is a four-level structure.Each of these layers is responsible for its functions, but one of the most important problems is the network addressing.For these purposes IP-address of the fourth version, that is a number composed of thirty two bits.It clearly identifies the network, which is a particular host, as well as directly, the host address.Obviously, the number of addresses is limited.
For proper addressing equipment you need to know exactly where in the address indicated by the network, and where the host.This mission takes the mask of the network, thus greatly simplifies the work of a large number of different network equipment, both passive and active.
Netmask clearly defines how many bits of the address belongs to the network, and what - to the address of the host.This technology can significantly increase the amount of possible addresses, in comparison with the technology a clear partition subnets into classes.It also allows you to avoid any conflicts arising in a case of finding the same address.
network mask allows you to divide large networks into smaller ones, which are divided, in turn, even smaller and so on, until you pass the thirty bits.But with the increasing number of networks decreases the number of hosts.Therefore, applying this technology need to be considered very carefully the necessary number of addresses for hosts.
Typically, the mask set number from nine to thirty.This is the number of characters in the binary code addresses, which is responsible for the network address.For example, for an address 220.127.116.11, if he has 24 network mask, network address is 18.104.22.168, and the address of the host 22.214.171.124-254 (as the broadcast address is 126.96.36.199).
order for all this to determine the subnet mask must be calculated according to certain rules.In the above example, the process is as follows.So, first we must translate the address into a binary number system.But it must be done so that you get four octets.The missing digits should be replaced with zeros before the number.Further, reduced net mask, or rather its number is written in the form of consecutive units in an amount corresponding to this number.It is more convenient to do it by themselves clearly address digit figure.Further notes on the address dash when an end unit on the mask and start at zero.And we get left - subnet address, on the right - the host address.Transferred back to a more conventional view of the decimal.That's all.
This task is not difficult, but very useful when building extensive networks on a large scale.Mask of the network can become a reliable assistant for the construction of a clear hierarchical and ordered structure.