The Domain Name System (DNS) is a hierarchical naming system for domains and other Internet resources. DNS can be viewed as an address book for the Internet; a primary function of DNS is mapping domain names to host IP addresses.
DNS is maintained as a distributed database system that employs a client/server model. Resolvers (client programs) query the database for information. Name servers (server programs) respond with information obtained from locally stored resource records.
ICANN has overall responsibility for DNS.DNS namespace
The DNS namespace can be viewed as an inverted tree with a root, nodes, and subtrees.
Each node is assigned a text label (except the root node, which is assigned a null, zero-length label). Each subtree represents a portion of the DNS database and can be viewed as a domain or subdomain.
A domain name is dot-concatenated sequence of text labels that lead to a particular node in the tree. Domain names can be up to 63 characters in length.
A domain is an administrative unit with its own autonomy and authority. A domain can be viewed as a subtree within the DNS domain namespace.
Domains can be referred to by level (top-level, second-level — see below) or by reference (see subdomain).
The root zone is the top-level zone in the DNS domain namespace. The root zone encompasses all Internet domains.
A top-level domain (TLD), sometimes referred to as a first-level domain, is a subdomain of the DNS root zone. Top-level domains consist of generic top-level domains (gTLD) and country code top-level domains (ccTLD).
A second-level domain (SLD) is a subdomain of a top-level domain.
A third-level domain is a subdomain of a second-level domain, and so on.
A subdomain is a subtree within a domain. The name of a subdomain will include the name of the domain it belongs to. For example, www.google.com is a subdomain of the google.com domain; and google.com is a subdomain of the .com domain. All domains are a subdomain of root.
A host is a computer connected to the Internet or other large network. Hosts connected to the Internet have IP addresses.
An Internet Protocol (IP) address is a series of numbers assigned to a device (computer, printer) that is connected to the Internet or other large network. IP addresses enable devices within a network to communicate with each other. IP addresses have two versions:
- IPv4 addresses
IP version 4 addresses consist of 32 bits and use a dotted-decimal notation
(field1.field2.field3.field4) – 220.127.116.11
- IPv6 addresses
IP version 6 addresses consist of 128 bits and use a hexadecimal notation
(field1:field2:field3 … :field8) – 1001:FE03:0DB9:AC10:7654:BA72:3210:FE05
A DNS name server is a system that responds to requests for information about domain resources.
Name servers are assigned to DNS nodes, have authority for one or more domains, and store the resources records for these domains.
A primary function of name servers is to translate domain names and host names into IP addresses (using the resource records). IP addresses, in turn, are used to locate domains, hosts, and other resources on the Internet.
Resource records provide information about domains and identify the resources within a domain. Resource records are stored on name servers.
Google Domains supports several types of resource records. For more information, see About resource records.
Note: Resource records are sometimes referred to as zone records because resource records can be stored in zone files (but don't have to be).
A URL (uniform resource locator) is the address of a resource on the Internet. For example, the address for Google’s main website is http://www.google.com.
A zone is an administrative unit that includes one or more DNS domains or subdomains.
A zone file is a text file that includes one or more resource records.
A zone record is a resource record.