DNS - Domain Name System — computer distributed system for obtaining information about domains. It is most often used to obtain an IP address by the host name (computer or device), obtaining information about mail routing, serving nodes for protocols in the domain.
A distributed DNS database is maintained using a hierarchy of DNS servers that communicate over a specific protocol.
The basis of DNS is the idea of a hierarchical structure of a domain name and zones. Each server responsible for the name can delegate responsibility for the further part of the domain to another server (from the administrative point of view - to another organization or person), which makes it possible to assign responsibility for the relevance of information to the servers of various organizations (people) responsible only for "their" part domain name.
DNS has the following characteristics:
Responsibility for different parts of the hierarchical structure is borne by different people or organizations.
The distribution of information storage.
Each node of the network must store only those data that fall within its area of responsibility and (possibly) the addresses of the root DNS servers.
Caching information. A node can store a certain amount of data not from its own area of responsibility to reduce the load on the network.
A hierarchical structure in which all nodes are combined into a tree, and each node can either independently determine the operation of the subordinate nodes, or delegate (transfer) them to other nodes.
Reservation. For the storage and maintenance of their nodes (zones), there are usually (usually) several servers, separated both physically and logically, which ensures the preservation of data and the continuation of work even in the event of a failure of one of the nodes.
DNS is important for the operation of the Internet, because to connect to a node, information about its IP address is required, and for people it's easier to remember alphabetic (usually meaningful) addresses than the sequence of IP address digits. In some cases, this allows you to use virtual servers, for example, HTTP servers, distinguishing them by request name. Initially, the conversion between domain and IP addresses was done using a special text file hosts, which was compiled centrally and automatically sent to each of the machines on its local network. With the growth of the Network, there was a need for an effective, automated mechanism, which became the DNS.
DNS is used primarily to convert character names to IP addresses, but it can also perform a reverse process. To do this, you use the existing DNS tools. The fact is that different data can be associated with a DNS record, including some symbolic name. There is a special in-addr.arpa domain, the entries in which are used to convert IP addresses to symbolic names. For example, to obtain a DNS name for the address 126.96.36.199, you can query the DNS server for the entry 188.8.131.52.in-addr.arpa and it will return the corresponding symbolic name. The reverse order of recording parts of the IP address is explained by the fact that in IP-addresses the high-order bits are located at the beginning, and in the symbolic DNS-names the older ones (closer to the root) are located at the end.