The domain name arpa is a

top-level domain A top-level domain (TLD) is one of the 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 root zone of the name space. For all domains in ...

(TLD) in the

Domain Name System The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned ...

(DNS) of the

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

. 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 of

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

and

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

addresses, respectively. The name originally was the

acronym An acronym is a word or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in '' NATO'' (''North Atlantic Treaty Organization''), but sometimes use syllables, a ...

for the Advanced Research Projects Agency (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 networks to implement the TCP/IP protocol suite. Both technologies became the technical fo ...

, 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. Th ...

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 and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and ...

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. ...

is identified by a numerical

IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ide ...

for identification and location addressing. Each host is also assigned a more memorable hostname, which often relates to the purpose or ownership of the host, and is used more conveniently in user interaction with network functions, such 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,, ''The Domain Name Plan and Schedule'', J. Postel, IETF (November 1983) 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, is implemented in the major uses of the domain ''arpa'': its subdomains ''in-addr.arpa'' for Internet Protocol version 4, 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 a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices ...

s through the ENUM 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 for non-unique DNS services in residential networking, to avoid the use of the top-level domain ''home.'', which would require DNSSEC signatures., ''Special-Use Domain home.arpa'', P. Pfister, T. Lemon, IETF (May 2018) In addition, the use of ''home.'' led to domain name leakage to the Internet root name servers. The authoritative name servers for home.arpa intercept locally unresolved queries for the domain and return addresses for certain blackhole servers.

History

The

, named for the Advanced Research Projects Agency (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 set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...

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., J. Postel, J. Reynolds, ''Domain Requirements'', IETF (October 1984) 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 reverse DNS lookup 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

. In March 2010, zone arpa was secured with digital signatures within the Domain Name System Security Extensions (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 number allocation, root zone management in the Domain Name System (DNS), media types, and other Intern ...

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

References

External links

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