It is customary to refer to a domain name as a symbolic designation that replaces the numeric addressing based on IP addresses on the Internet. The numeric addressing used in the processing of route tables is ideal for computer use, but presents significant difficulties for the user to remember. Mnemonically meaningful domain names come to the rescue.
Establishing connections on the Internet is carried out in numerical groups of 4 values, separated by a "." and named IP addresses. The symbolic names of the domain name complex are a service designed to make it easier to find the required IP address on the network. The technical indicator of a domain name is the symbol "." in the user's email address. So, in the address google.com, the domain name will be com. The domain name itself is not able to provide access to the required Internet resource. The procedure for using a mnemonic name consists of two stages: - determining the IP address by name in the hosts file, which contains tables of correspondence between the IP address and the computer name; - establishing a connection to a remote web resource at a specific IP address. The main task of the DNS service is to obtain The IP addresses to establish the connection, which makes this service auxiliary to the TCP / IP protocol. The "." is a separator of the components of a domain name, although for practical purposes it is usually taken as a designation of a root domain that does not have its own designation. Root - the whole set of Internet hosts - subdivided into: - first-level domains - gov, edu, com, net; - national domains - uk, jp, ch, etc.; - regional domains - msk; - corporate domains - organizational domains The preservation of the usual tree-like structure of domain names has led to the use of an established terminology - root, tree nodes, leaf. The term "host" in this hierarchy is assigned to a leaf that does not have a single node under it. The fully qualified hostname becomes a sequential listing of all intermediate nodes between the root and the leaf, separated by the "." from left to right: ivan.net.abcd.ru, where ru is the root of the tree, abcd is the name of the organization, ivan is the leaf of the tree (host).
