DNS

DOMAIN NAME SYSTEM

The Domain Name System (DNS) is a hierarchical and decentralized naming system for computers, services or other resources connected to the Internet or a private network. It associate various information with domain names assigned to each of the participating entities. Most prominently, it translate more readily memorized domain names to the numerical IP address needed for locating and Identifying services and devices with the underlying network protocols. By providing World wide, distributed directory service, the domain name system has been an essential component of the functionality of the Internet since 1985. 

The Domain Name System delegates the responsibility of assigning domain names and mapping those names to Internet resources by designating authoritative name servers for each domain. Network administrators may delegate authority over sub-domains of their allocated name space to other name servers. This mechanism provides distributes and fault-tolerant service and was designed to avoid a single large central database. 

Domain Name Space

The Domain name space consists of a tree data structure. Each node or leaf in the tree has a label and zero or more resource records (RR) which hold information associated with the domain name. The domain name itself consists of the label , concatenated with the name of it's parent node. 

The tree sub-divides into zones beginning at the root node. A DNS zone may consists of only one domain or may be consists of many domains and sub-domains depending on the administrative choices of the zone manager. DNS can also be partitioned according to class where the separate classes can be thought of as an array of parallel namespace trees.

How DNS works

DNS servers answer questions from both inside and outside their domains. When a server receives a request from outside the domain for information about a name or address inside the domain, it provides the authoritative answers. When a server receives a request from inside its own domain for information about a name or address outside that domain, it passes the request out to another server. Usually, this server is one managed by its internet service provider (ISP).

DNS structure

A domain name is made of multiple parts, called labels. The domain hierarchy is read from right to left with each section denoting a subdivision. The top-level domain  is what appears after the period in the domain name. A few examples of top-level domains are .com, .org and .edu, but there are many others that can be used. Some may denote a country code or geographic location such as .us for the United States or .ca for Canada.

Each label to the left denotes another subdomain to the right. So for example, “techtarget” is a subdomain of .com. and “www.” is a subdomain of techtarget.com. There can be up to 127 levels of subdomains, and each label can have up to 63 characters. The total domain character length can have up to 253 characters. Other rules include not starting or ending labels with hyphens and not having a fully numeric top-level domain name.