The domain name arpa is a

top-level domain A top-level domain (TLD) is one of the domain name, domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain. The top-level domain names are installed in the DNS root zone, root zone of the nam ...

(TLD) in the

Domain Name System The Domain Name System (DNS) is a hierarchical and distributed name service that provides a naming system for computers, services, and other resources on the Internet or other Internet Protocol (IP) networks. It associates various information ...

(DNS) of the

Internet The Internet (or internet) is the Global network, global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a internetworking, network of networks ...

. It is used predominantly for the management of technical network infrastructure. Prominent among such functions are the subdomains ''in-addr.arpa'' and ''ip6.arpa'', which provide namespaces for

reverse DNS lookup In computer networks, a reverse DNS lookup or reverse DNS resolution (rDNS) is the querying technique of the Domain Name System (DNS) to determine the domain name associated with an IP address – the reverse of the usual "forward" DNS lookup o ...

IPv4 Internet Protocol version 4 (IPv4) is the first version of the Internet Protocol (IP) as a standalone specification. It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. ...

and

IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...

addresses, respectively. The name originally was the

acronym An acronym is a type of abbreviation consisting of a phrase whose only pronounced elements are the initial letters or initial sounds of words inside that phrase. Acronyms are often spelled with the initial Letter (alphabet), letter of each wor ...

for the

Advanced Research Projects Agency The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Adva ...

(ARPA), the funding organization in the United States that developed the

ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first computer networks to implement the TCP/IP protocol suite. Both technologies became the tec ...

, the precursor of the Internet. It was the first domain defined for the network in preparation for a hierarchical naming system for the delegation of authority, autonomy, and responsibility. It was originally intended only to serve in a temporary function for facilitating the systematic naming of the ARPANET computers. However, it became practically difficult to remove the domain after infrastructural uses had been sanctioned. As a result, the name was redefined as the

backronym A backronym is an acronym formed from an already existing word by expanding its letters into the words of a phrase. Backronyms may be invented with either serious or humorous intent, or they may be a type of false etymology or folk etymology. The ...

Address and Routing Parameter Area. Domain-name registrations in arpa are not possible, and new subdomains are infrequently added by the

Internet Engineering Task Force The Internet Engineering Task Force (IETF) is a standards organization for the Internet standard, Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster ...

Purpose

Each computer using the

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. IP ...

is identified by a numerical

IP address An Internet Protocol address (IP address) is a numerical label such as that is assigned to a device connected to a computer network that uses the Internet Protocol for communication. IP addresses serve two main functions: network interface i ...

for identification and location addressing. Each host is also assigned a more memorable

hostname In computer networking, a hostname (archaically nodename) is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication, such as the World Wide Web. Hos ...

, which often relates to the purpose or ownership of the host, and is used more conveniently in user interaction with network functions, such as when connecting to or accessing a resource. Originally, the mapping between names and addresses was a cumbersome mechanical process using lookup tables distributed as computer files between network administrators. The

(DNS) solved this inefficiency by automating the lookup function with a hierarchical naming system using domain names. When a user requests a network service using a domain name, the protocol implementation (''protocol stack'') translates the name to an address that can be used to reach a remote host. This naming function, often called ''forward resolution'', was the original purpose of the top-level domain "ARPA". It was the first domain defined in the first naming system of the nascent Internet, and was supposed to be an initial container domain for all then-existing ARPANET hosts. The next stage of development of the naming architecture foresaw the establishment of specific domains for other purposes based on certain requirements.

Reverse IP address mapping

In many applications the reverse of the name-to-address mapping is also required. The host receiving a service request may require the domain name of the originating computer, for example, to customize the service, or for verification purposes. This latter function, called

Reverse DNS lookup In computer networks, a reverse DNS lookup or reverse DNS resolution (rDNS) is the querying technique of the Domain Name System (DNS) to determine the domain name associated with an IP address – the reverse of the usual "forward" DNS lookup o ...

, is implemented in the major uses of the domain ''arpa'': its subdomains ''in-addr.arpa'' for

Internet Protocol version 4 Internet Protocol version 4 (IPv4) is the first version of the Internet Protocol (IP) as a standalone specification. It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks ...

, and ''ip6.arpa'' for

. Conceptually similar lookup and mapping functionality is provided by other subdomains of ''arpa'' for specific types of data.

Telephone number mapping

The domain e164.arpa provides a lookup function that retrieves information associated with

telephone number A telephone number is the address of a Telecommunications, telecommunication endpoint, such as a telephone, in a telephone network, such as the public switched telephone network (PSTN). A telephone number typically consists of a Number, sequ ...

s through the

ENUM Telephone number mapping is a system of unifying the international telephone number system of the public switched telephone network with the Internet addressing and identification name spaces. Internationally, telephone numbers are systematicall ...

service. This service may be used to obtain the name of a computer that is capable of routing telecommunication requests for a registered telephone number, or obtain an email address to contact the subscriber of a specific telephone number.

Residential networking

The domain name ''home.arpa'' was reserved by the Internet Engineering task force in May 2018 as a

special-use domain name A special-use domain name is a domain name that is defined and reserved in the hierarchy of the Domain Name System of the Internet for special purposes. The designation of a reserved special-use domain is authorized by the Internet Engineering Ta ...

for non-unique DNS services in residential networking, to avoid the use of the top-level domain ''home.'', which would require DNSSEC signatures. In addition, the use of ''home.'' led to domain name leakage to the Internet root name servers. The

authoritative name server A name server is a computer application that implements a network service for providing responses to queries against a directory service. It translates an often humanly meaningful, text-based identifier to a system-internal, often numeric identi ...

s for home.arpa are the AS112 blackhole servers, which prevent leaked queries for home.arpa from burdening the root servers.

History

The

, named for the

(ARPA), was launched in 1969, and is considered the earliest predecessor of the

. The agency's name was adopted as the name for the first formal name space of the network after it had transitioned to

TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are ...

networking in January 1983. The name was used as a naming suffix for all then-existing ARPANET hosts. Hierarchical domain-style names were intended to support delegation of responsibility and authority for adding future hosts to the network. With the formal development of such a hierarchical naming system, the domain also became one of the inaugural members of a set of domain names for specific types of network members, namely com for commercial users, org for organizations, edu for educational institutions, gov for government entities, and mil for networks of the United States military. It was expected that the use of ''arpa'' would be temporary and that the existing systems would be migrated to other domains. But ''arpa'' also provided e-mail addresses associated with the Network Information Center, which administered the naming system. After serving the transitional purpose, it proved impractical to remove the domain. The domain ''in-addr.arpa'' had been installed for

of IP addresses. Originally, the IETF intended that new infrastructure databases would be created in the top-level domain ''int''. In May 2000, this policy was reversed and it was decided that the top-level domain ''int'' should be restricted to use by international organizations. ''Arpa'' was retained for its long-standing purpose, but its full name was changed to the ''Address and Routing Parameter Area'', making the zone name a

. Registrations of internet infrastructure services in .int made prior to this policy change, were optionally grandfathered in and not required to move to .arpa. In March 2010, zone arpa was secured with digital signatures within the

Domain Name System Security Extensions The Domain Name System Security Extensions (DNSSEC) is a suite of Extension Mechanisms for DNS, extension specifications by the Internet Engineering Task Force (IETF) for securing data exchanged in the Domain Name System (DNS hijacking, DNS) in In ...

(DNSSEC).

Subdomains

Subdomains of ''arpa'' are created by resolution in the work groups of the Internet Engineering Task Force via the

Request for Comments A Request for Comments (RFC) is a publication in a series from the principal technical development and standards-setting bodies for the Internet, most prominently the Internet Engineering Task Force (IETF). An RFC is authored by individuals or ...

process, and are maintained by the

Internet Assigned Numbers Authority The Internet Assigned Numbers Authority (IANA) is a standards organization that oversees global IP address allocation, Autonomous system (Internet), autonomous system number allocation, DNS root zone, root zone management in the Domain Name Syste ...

(IANA). The DNS zone ''arpa'' has the following subdomains:

References

(987)

External links

arpa. zone file
{{DEFAULTSORT:ARPA Generic top-level domains Internet properties established in 1985 1985 establishments in the United States