The representation of an IPv4 address in the DNS system.
The representation of an IPv6 address in the DNS system.
The ASCII-compatible encoded (ACE) representation of an internationalized domain name, i.e. how it is transmitted internally within the DNS protocol. A-labels always commence the with the prefix "xn--". Contrast with U-label.
A subcategory of private IP address. See Private IP Addresses.
A subset of IRIS for performing registration lookups on IP addresses.
Originally a reference to the US Government agency that managed some of the Internet’s initial development, now a top-level domain used solely for machine-readable use by computers for certain protocols — such as for reverse IP address lookups, and ENUM. The domain is not designed for general registrations. IANA manages .ARPA in conjunction with the Internet Architecture Board.
ASCII (American Standard Code for Information Interchange)
The standard for transmitting English (or "Latin") letters over the Internet. DNS was originally limited to only Latin characters because it uses ASCII as its encoding format, although this has been expanded using Internationalised Domain Names for Applications.
Authoritative Name Server
a domain name server configured to host the official record of the contents of a DNS zone. Each domain name must have a set of these so computers on the Internet can find out the contents of that domain. The set of authoritative name servers for any given domain must be configured as NS records in the parent domain.
Autonomous System Number (AS number, ASN)
A number used by Internet routing protocols to uniquely identify the routing policy of a particular network operator. They can be considered to be similar to a ‘postcode’ used for physical mail. They are allocated to network operators via regional Internet registries.
the combination of a recursive name server and a caching name server.
Country-code Name Supporting Organization (ccNSO)
A component of ICANN’s policy development forums (a "constituency") that is responsible for discussing and developing policy relating to how ccTLDs are delegated.
Country-code top-level domain (ccTLD)
A class of top-level domains only assignable to represent countries listed in the ISO 3166-1 standard. At present these are two-letter codes like .DE etc., however in the future it is expected there will be non-Latin equivalents also available. Much of the policy-making for individual country-code top-level domains is vested with a local sponsoring organization, as opposed to other top-level domains where ICANN sets the policy. It is a requirement that ccTLDs are operated within the country they are designated so appropriate local laws, governments etc. have a say in how the domain is run.
Cross-Registry Information Service Protocol (CRISP)
The name of the working group at the IETF that developed the Internet Registry Information Service (IRIS), a next-generation WHOIS protocol replacement.
A subset of IRIS for performing checks on whether a domain name is available to register. It is more lightweight, and has less privacy implications, than DREG as it does not transmit registration data other than simple availability.
Any transfer of responsibility to another entity. In the domain name system, one name server can provide pointers to more useful name servers for a given request by returning NS records. On an administrative level, sub-domains are delegated to other entities. IANA also delegates IP address blocks to regional Internet registries.
A technology that can be added to the Domain Name System to verify the authenticity of its data. The works by adding verifiable chains of trust that can be validated to the domain name system.
A section of the Domain Name System name space. By default, the Root Zone contains all domain names, however in practice sections of this are delegated into smaller zones in a hierarchical fashion. For example, the .COM zone would refer to the portion of the DNS delegated that ends in .COM.
A unique identifier with a set of properties attached to it so that computers can perform conversions. A typical domain name is "icann.org". Most commonly the property attached is an IP address, like "220.127.116.11", so that computers can convert the domain name into an IP address. However the DNS is used for many other purposes. The domain name may also be a delegation, which transfers responsibility of all sub-domains within that domain to another entity. domain name label a constituent part of a domain name. The labels of domain names are connected by dots. For example, "www.iana.org" contains three labels — "www", "iana" and "org". For internationalised domain names, the labels may be referred to as A-labels and U-labels.
Domain Name Registrar
An entity offering domain name registration services, as an agent between registrants and registries. Usually multiple registrars exist who compete with each other, and are accredited. For most generic top-level domains, domain name registrars are accredited by ICANN.
Domain Name Registry
A registry tasked with managing the contents of a DNS zone, by giving registrations of sub-domains to registrants.
Domain Name Server
A general term for a system on the Internet that answers requests to convert domain names into something else. These can be subdivided into authoritative name servers, which store the database for a particular DNS zone; as well as recursive name servers and caching name servers.
Domain Name System (DNS)
The global hierarchical system of domain names. A global distributed database contains the information to perform the domain name conversations, and the most central part of that database, known as the root zone is coordinated by IANA.
Extensible Provisioning Protocol (EPP)
A protocol used for electronic communication between a registrar and a registry for provisioning domain names.
first come, first served (FCFS)
IANA registries are administered on a "first come, first served" basis.
fully-qualified domain name (FQDN)
A complete domain name including all its components, i.e. "www.icann.org" as opposed to "www".
A document, formally known as the Principles for the Delegation and Administration of ccTLDs. This document was developed by the ICANN Governmental Advisory Committee and documents a set of principles agreed by governments on how ccTLDs should be delegated and run.
Generic top-level domains (gTLDs)
A class of top-level domains that are used for general purposes, where ICANN has a strong role in coordination (as opposed to country-code top-level domains, which are managed locally).
An explicit notation of the IP address of a name server, placed in a zone outside of the zone that would ordinarily contain that information.. All name servers are in-bailiwick of the Root Zone, therefore glue records is required for all name servers listed there. Also referred to as just "glue".
A file stored in DNS software (i.e. recursive name servers) that tells it where the DNS root servers are located.
The name of a computer. Typically the left-most part of a fully-qualified domain name.
A component of RFCs that refer to any work required by IANA to maintain registries for a specific protocol.
The contract between ICANN and the US Government that governs how various IANA functions are performed.
Internationalised domain name (IDN)
A domain name that uses characters outside the 37 characters allowed by the "LDH rule", using a system known as IDNA. This allows for domain names in non-Latin scripts, such as Arabic, Japanese or Cyrillic.
Internet Architecture Board (IAB)
The oversight body of the IETF, responsible for overall strategic direction of Internet standardisation efforts. The IAB works with ICANN on how the IANA protocol parameter registries should be managed. The IAB is an activity of the Internet Society, a non-profit organization.
Internet Assigned Numbers Authority (IANA)
A department of ICANN tasked with providing various Internet coordination functions, primarily those described in a contract between ICANN and the US Government. The functions relate to ensuring globally-unique protocol parameter assignment, including management of the root of the Domain Name System and IP Address Space. ICANN staff within this department is often referred to as "IANA Staff".
Internet Coordination Policy (ICP)
A series of documents created by ICANN between 1999 and 2000 describing management procedures.
Internet Engineering Steering Group (IESG)
The committee of area experts of the IETF’s areas of work, that acts as its board of management.
Internet Engineering Task Force (IETF)
The key Internet standardisation forum. The standards developed within the IETF are published as RFCs.
A top-level domain devoted solely to international treaty organizations that have independent legal personality. Such organizations are not governed by the laws of any specific country, rather by mutual agreement between multiple countries. IANA maintains the domain registry for this domain.
Internet Protocol (IP)
The fundamental protocol that is used to transmit information over the Internet. Data transmitted over the Internet is transmitted using the Internet Protocol, usually in conjunction with a more specialised protocol. Computers are uniquely identified on the Internet using an IP Address.
Internet Registry Information Service (IRIS)
A sophisticated protocol for looking up registration data. It is designed to supplant the WHOIS protocol.
Internet Telephony Administrative Domain (ITAD)
A unique numbering system used by Telephone Routing over Internet Protocol (TRIP) to label phone services within an organization.
Interim Trust Anchor Repository (ITAR)
A proposed IANA service whereby the trust anchors for top-level domains can be listed separately from the DNS root zone. This is a temporary measure due to the inability to use DNSSEC to sign the root zone.
A unique identifier for a device on the Internet. The identifier is used to accurately route Internet traffic to that device. IP addresses must be unique on the global Internet.
Internet Protocol version 4. Refers to the version of Internet protocol that supports 32-bit IP addresses.
Internet Protocol version 6. Refers to the version of Internet protocol that supports 128-bit IP addresses.
a type of record in a DNS zone that signifies part of that zone is delegated to a different set of authoritative name servers.
the domain above a domain in the DNS hierarchy. For all top-level domains, the Root Zone is the parent domain. The Root Zone has no parent domain as it is as the top of the hierarchy. Opposite of sub-domain.
Private enterprise numbers (PENs)
A unique numbering system used by several different Internet protocols (such as SNMP and LDAP) that use Abstract Notation Syntax One (ASN.1).
The representation of a IP address to domain name mapping in the DNS system.
Recursive Name Server
A domain name server configured to perform DNS lookups on behalf of other computers.
The transfer of a delegation from one entity to another. Most commonly used to refer to the redelegation process used for top-level domains.
A special type of root zone change where there is a significant change involving the transfer of operations of a top-level domain to a new entity.
Regional Internet Registry (RIR)
A registry responsible for allocation of IP address resources within a particular region.
The entity that has acquired the right to use an Internet resource. Usually this is via some form of revocable grant given by a registrar to list their registration in a registry.
An entity that can act on requests from a registrant in making changes in a registry. Usually the registrar is the same entity that operates a registry, although for domain names this role is often split to allow for competition between multiple registrars who offer different levels of support.
The authoritative record of registrations for a particular set of data. Most often used to refer to domain name registry, but all protocol parameters that IANA maintains are also registries.
The entity that runs a registry.
A method of translating an IP address into a domain name, so-called as it is the opposite of a typical lookup that converts a domain name to an IP address.
A series of Internet engineering documents describing Internet standards, as well as discussion papers, informational memorandums and best practices. Internet standards that are published in an RFC originate from the IETF. The RFC series is published by the RFC Editor.
the authoritative name servers for the Root Zone.
The top of the domain name system hierarchy. The root zone contains all of the delegations for top-level domains, as well as the list of root servers, and is managed by IANA.
Root Zone Management RZM
The management of the DNS Root Zone by IANA.
A project to automate many aspects of the Root Zone Management function within IANA. Based on a software tool originally called "eIANA".
The entity acting as the trustee of a top-level domain on behalf of its designated community.
A domain that resides within another domain. For example, "www.icann.org" is a sub-domain of "icann.org", and "icann.org" is a sub-domain of "org". Sub-domains are entrusted to other entities through a process of delegation.
Top-level domain (TLD)
The highest level of subdivisions with the domain name system. These domains, such as ".COM" and ".UK" are delegated from the DNS Root zone. They are generally divided into two distinct categories, generic top-level domains and country-code top-level domains.
A known good cryptographic certificate that can be used to validate a chain of trust.
trust anchor repository (TAR)
Any repository of public keys that can be used as trust anchors for validating chains of trust. See Interim Trust Anchor Repository (ITAR) for one such repository for top-level domain operators using DNSSEC.
An entity entrusted with the operations of an Internet resource for the benefit of the wider community. In IANA circles, usually in reference to the sponsoring organization of a top-level domain.
The Unicode representation of an internationalised domain name, i.e. how it is shown to the end-user. Contrast with A-label.
A standard describing a repertoire of characters used to represent most of the worlds languages in written form. Unicode is the basis for internationalized domain names.
Unsponsored top-level domain
a sub-classification of generic top-level domain, where there is no formal community of interest.
A standard used for transmitting Unicode characters.
In the context of internationalised domain names, an alternative domain name that can be registered, or mean the same thing, because some of its characters can be registered in multiple different ways due to the way the language works. Depending on registry policy, variants may be registered together in one block called a variant bundle. For example, "internationalise" and "internationalize" may be considered variants in English.
A collection of multiple domain names that are grouped together because some of the characters are considered variants of the others.
A type of IDN table that describes the variants for a particular language or script. For example, a variant table may map Simplified Chinese characters to Traditional Chinese characters for the purpose of constructing a variant bundle.
A simple plain text-based protocol for looking up registration data within a registry. Typically used for domain name registries and IP address registries to find out who has registered a particular resource. (Usage note: not "Whois" or "whois")
Used to refer to parts of a registry’s database that are made public using the WHOIS protocol, or via similar mechanisms using other protocols (such as web pages, or IRIS). Most commonly used to refer to a domain name registry’s public database.
An interface, usually a web-based form, that will perform a look-up to a WHOIS server. This allows one to find WHOIS information without needing a specialised computer program that speaks the WHOIS protocol.
A system running on port number 43 that accepts queries using the WHOIS protocol.
The format of data when it is transmitted over the Internet (i.e. "over the wire"). For example, an A-label is the wire format of an internationalised domain name; and UTF-8 is a possible wire format of Unicode.
A machine-readable file format for storing structured data. Used to represent web pages (in a subset called HTML) etc. Used by IANA for storing protocol parameter registries.