Address record. A DNS record that maps a domain name to a corresponding IPv4 address.

Quad-A address record. A DNS record that maps a domain name to a corresponding IPv6 address.

Access control list. A list of permissions associated with a computer system or system resource. An ACL enumerates the users or processes granted access to resources and the operations permitted on or within a given resource. Typically, each entry in an ACL specifies a subject and operation.

Authoritative name servers store information about assigned groups of domain names and respond to queries for information, including mapping assigned domain names to their corresponding IP addresses. The group of domain names a name server is responsible for is called a zone. Authoritative name servers are responsible for providing recursive resolvers with authoritative data for their assigned zones and keeping data about them data current.

Country-code top-level domain. A two-letter TLD allocated to or reserved for a country, sovereign state or territory by the Internet Assigned Numbers Authority (IANA).

Canonical Name record. A DNS record specifying a domain name as an alias for another domain name. A CNAME record never points to an IP address, only to another domain name.

Domain Name System. The distributed name service and record that provides a system for registered, unique, human-readable domain names to be translated into numerical IP addresses. The DNS, an integral part of the internet since 1985, delegates the responsibility of assigning domain names and mapping names to IP addresses via authoritative name servers for each domain, avoiding the creation and dependance on a single, central database for a more secure, stable and resilient distributed system.

See Zone, zone file, DNS zone

Domain Name System Security Extensions. A suite of specifications enabling secure domain name lookups by incorporating a chain of cryptographic signatures to into the lookup process, developed by the Internet Engineering Task Force (IETF). Using DNSSEC, resolvers can validate that query responses are generated by authenticated DNS servers.

Fully Qualified Domain Name. A domain name that specifies an exact location in the Domain Name System hierarchy. All domain levels are specified in a FQDN, including the top-level domain (TLD) and the root zone, with each level separated by a “.” known as a “full stop.” For example, www.dnib.com is a FQDN.

generic top-level domain. A top-level domain (TLD) assigned by the Internet Assigned Numbers Authority (IANA) for generic or general use.

Internationalized Domain Name. A domain name in which one or more of its labels contain characters other than ASCII letters, digits or hyphens. Because IDNs support the use of Unicode characters, they can include characters from local languages and scripts. IDNs are implemented using the Internationalized Domain Names in Applications (IDNA) protocol.

A U.S. based non-profit corporation founded in 1994 to support the infrastructure and growth of the internet by developing and maintaining its core protocols, open-source software and operations. ISC is one of 12 root server operators (RSOs), responsible for the F-Root identity and its network of root servers.

Internet Protocol address. A unique character string identifying each device using the Internet Protocol on a network. The Internet Protocol is the network communications layer by which data packets are defined and delivered from a source host to a destination host.

Internet Protocol version 4 is set of rules enabling devices to communicate on the internet. IPv4 uses a 32-bit address space for logical routing of internet traffic, forwarding multiple packets of information from a source host to the next appropriate router using the best-effort delivery model to eventually get the packets to the intended destination host.

Introduced by the IETF in 1982 and originally deployed on ARPANET in 1983, IPv4 is the first version of the IP as a standalone specification. The 32-bit address space is limited to 4,294,967,296 unique addresses and will eventually be succeeded by IPv6.

In the DNS, hostnames and domain names are mapped to IPv4 addresses by an A record.

Internet Protocol version 6 is a set of rules enabling devices to communicate on the internet using 128-bit addresses. IPv6 addresses are represented by eight groups of four hexadecimal digits each, separated by colons. Adhering to the design principals of its predecessor, IPv4, IPv6 routes internet traffic using multi-packet routing to break data into smaller pieces to move across the internet from a source host to the intended destination. However, IPv6 specifies a new packet format minimizing packet header processing by routers and these two significantly different headers mean the IPv4 and IPv6 protocols are not interoperable.

IPv6 was ratified as an internet standard by the IETF in July 2017 and deployment has been in progress since the mid-2000s.

In the DNS, hostnames and domain names are mapped to IPv6 addresses by a AAAA record.

new generic TLD, new gTLD. The generic top-level domains (gTLDs) created in the initial development of the Domain Name System (DNS) were limited in number and initially restricted to specific types of registrants, such as educational institutions for .edu. After ICANN was established in 1998, a system for approving more TLDs was established and additional TLDs were introduced over the next decade. In 2012, ICANN launched the new gTLD program, receiving more than 1,900 applications for gTLDs. Since then, more than 1,300 new gTLDs have been approved and delegated.

Any individual or entity who registers a domain name.

To register a domain name, the registrant enters into a contract with a registrar, which registers and maintains the domain name on behalf of the registrant.

Registrants manage registered domain names through registrars; a registrant submits changes to the appropriate registrar and the registrar communicates the changes to the registry operator. In some cases, registrants may use a reseller, which can act on behalf of registrants, registering and managing domain names through a registrar.

A company through which individuals and entities register domain names.

To register a domain name, the registrant enters into a contract with a registrar, which registers and maintains the domain name on behalf of the registrant.

A registrar verifies that requested domain names meet registry requirements, collects required information from registrants, submits each domain name to the appropriate registry operator and ensures registrant information is available in WHOIS/RDAP.

Registrars manage the registered domain name on behalf of the registrant; a registrant submits the changes to the registrar and the registrar communicates the changes to the registry operator.

A registrar that has entered into a Registrar Accreditation Agreement (RAA) with ICANN is referred to as an ICANN-accredited registrar.

An HTTP-based protocol that provides access to information about current domain name registrations and Internet Protocol address allocations. RDAP databases for assigned IP numbers are maintained by the Regional Internet Registries; databases for registered names are maintained under an ICANN agreement, with a temporary specification to deconflict ICANN and GDPR policies.

The RDAP profile was proposed by ICANN in August 2018, though discussions about the need for the technical evolution of registrant information databases and a successor to the WHOIS protocol began in 2010. The global amendment to the base gTLD agreement, making RDAP an official requirement, was effective Aug. 7, 2023, with a compliance deadline of Feb. 3, 2024, for gTLD registry operators and registrars.

An ICANN proof-of-concept project for a centralized ticketing system for requests to access nonpublic registration data related to gTLDs. Launched in November 2023, RDRS is expected to run for two years.

A set of online services registrars and registry operators of top-level domains provide to enable public access to domain name registration data. Currently, RDS are available for generic top-level domains through the WHOIS protocol and HTTP-based protocol directory services. Individual Regional Internet Registries also use RDS maintain a database of IP addresses that have been assigned in their region.

The registry is the authoritative master database of the domain names registered in a top-level domain (TLD). Each TLD is associated with a registry containing the record for each domain name that exists in the TLD.

The registry operator is the entity responsible for managing a TLD’s registry, under the accreditation and mandates of Internet Assigned Numbers Authority (IANA). Registry operators manage domain name allocation, maintain zone files and ensure the security, stability and resiliency of the DNS for the TLD. The registry operator responds to requests from registrars to add, delete or modify domain names; makes the corresponding changes to the registry; manages and maintains a TLD’s authoritative name servers and zone files; and resolves DNS record queries for domain names within the TLD. Registry operators are contractually obligated and accountable for following ICANN policies and agreements.

A registry service provider (RSP) implements and manages technical infrastructure for a TLD on behalf of a registry operator. An RSP takes on responsibilities that may include domain name allocation, DNS resolution, WHOIS/RDAP services and registry database management from the Registry Operator. RSPs must be evaluated by ICANN.

A contract between a registry operator and an ICANN-accredited registrar. This contract defines the terms under which a registrar agrees to perform domain name registration services for a designated generic top-level domain.

The organizations responsible for managing the root service on the Internet Protocol (IP) addresses specified in the root zone and the root hints file. RSOs are volunteer organizations, receiving no compensation. RSOs are required by ICANN policy documents and protocols to be neutral, impartial and committed to providing service to all users, all networks and all top-level domains (TLDs) equally and to serving the IANA global root DNS namespace with complete and unmodified data.

The set of root servers, across all operators, collectively implementing the root service.

Top-level domain. In the DNS namespace hierarchy, the TLD is the last part of any fully qualified domain name (FQDN). In “https://www.dnib.com” the TLD is “.com”. The Internet Corporation for Assigned Names and Numbers (ICANN) has authority over TLDs use and delegates these responsibilities as needed. Types of TLDs include generic TLDs (gTLDs), country-code TLDs (ccTLDs), sponsored TLDs, reserved TLDs and more.

Uniform Resource Locator. A URL incorporates a domain name, along with other detailed information, to create a complete web address directing a browser to a specific web page or location on the internet. Though often used interchangeably, a URL and a domain name are not the same thing. URL syntax combines a protocol (http), a host name (www.dnib.com) and file path syntax (index.html), using slashes to separate directory and file names (http://www.dnib.com/learning-center)

Verisign, founded in 1995 as a spin-off of RSA Security, is a global provider of critical internet infrastructure and domain name registry services, enabling internet navigation for many of the world’s most recognized domain names. Verisign helps enable the security, stability and resiliency of the DNS and the internet by providing root zone maintainer services, operating two of the 13 global internet root servers and providing registration services and authoritative resolution for the .com and .net TLDs, among others.

One type of identifier, outside of the DNS, in an alternative namespace, typically built on a blockchain.

The protocol underlying the public database that holds human-readable versions of information collected from registrants when a domain name is registered. Established in 1982 and currently administered by ICANN, the information in the distributed WHOIS database – including registrants’ and registrars’ names, phone numbers, emails and addresses – was originally intended to enable contact with registrants to resolve technical issues. The WHOIS protocol and systems were succeeded by the RDAP protocol and data systems in January 2025.

A specific, distinctly managed part of the Domain Name System (DNS) namespace. A DNS zone is delegated in the configuration of a domain name server and defined in the zone file, an operating system text file containing all mapping between domain names and resource records, including IP addresses.

A zone is an organizational distinction, not necessarily a physical one, as multiple zones can reside on the same server.