Editing .arpa

{{Short description|Internet top-level domain}}
{{Use mdy dates|date=June 2020}}
{{Use American English|date=March 2021}}
{{Infobox top level domain
|name=.arpa
||introduced={{start date and age|1985|1|1}}
|type=Infrastructure domain
|status=Active
|registry=[[Internet Assigned Numbers Authority|IANA]]
|sponsor=[[Internet Architecture Board]]
|intendeduse=A temporary TLD to facilitate the transition from [[ARPANET]] to the DNS.
|actualuse=Internet infrastructure such as reverse DNS lookup.
|restrictions=No domain registrations possible, new subdomains rarely added
|structure=Second-level domains used for various functions related to Internet infrastructure as defined by RFCs.
|document={{IETF RFC|3172}}; {{IETF RFC|9120}}
|disputepolicy=None
|website=[https://www.iana.org/domains/arpa IANA .arpa info]
|dnssec=Yes
}}
The domain name '''arpa''' is a [[top-level domain]] (TLD) in the [[Domain Name System]] (DNS) of the [[Internet]]. 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]] and [[IPv6]] addresses, respectively.

The name originally was the [[acronym]] for the [[Advanced Research Projects Agency]] (ARPA), the funding organization in the United States that developed the [[ARPANET]], 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]] '''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]].

==Purpose==
Each computer using the [[Internet Protocol]] is identified by a numerical [[IP address]] for identification and location addressing.{{Ref RFC|791}} 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 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 [[Domain Name System]] (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,{{Ref RFC|881}} 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.<ref name=rfc881/>

===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 [[IPv6]].

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]]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.{{Ref RFC|8375}} In addition, the use of ''home.'' led to domain name leakage to the Internet root name servers. The [[authoritative name server]]s for home.arpa are the AS112 [[blackhole server]]s<ref>{{Cite report |url=https://datatracker.ietf.org/doc/html/rfc8375.html |title=Special-Use Domain 'home.arpa.' |last=Pfister |first=Pierre |last2=Lemon |first2=Ted |date=May 2018 |publisher=Internet Engineering Task Force |issue=RFC 8375}}</ref>, which prevent leaked queries for home.arpa from burdening the root servers<ref>{{Cite report |url=https://datatracker.ietf.org/doc/html/rfc6305.html |title=I'm Being Attacked by PRISONER.IANA.ORG! |last=Maton |first=William F. |last2=Abley |first2=Joe |date=July 2011 |publisher=Internet Engineering Task Force |issue=RFC 6305}}</ref>.

==History==
The [[ARPANET]], named for the [[Advanced Research Projects Agency]] (ARPA), was launched in 1969, and is considered the earliest predecessor of the [[Internet]]. 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]] networking in January 1983.{{Ref RFC|881}} 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|com]] for commercial users, [[.org|org]] for organizations, [[.edu|edu]] for educational institutions, [[.gov|gov]] for government entities, and [[.mil|mil]] for networks of the United States military.{{Ref RFC|920}}

It was expected that the use of ''arpa'' would be temporary and that the existing systems would be migrated to other domains.<ref name=rfc920/> 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.{{Ref RFC|1035|rsection=3.5}}

Originally, the IETF intended that new infrastructure databases would be created in the top-level domain [[.int|''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.<ref name="IAB Statement2">{{cite web|url=https://www.iab.org/documents/docs/iab-arpa-stmt.txt|title=IAB Statement on Infrastructure Domain and Subdomains|access-date=2019-08-01|archive-date=2003-08-27|archive-url=https://web.archive.org/web/20030827065632/https://www.iab.org/documents/docs/iab-arpa-stmt.txt|df=dmy-all}}</ref>  ''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 [[backronym]].{{Ref RFC|3172|rp=7|quote=Further, as indicated by DARPA, the arpa TLD string should be given a different expansion such as "Address and Routing Parameter Area" to avoid any implication that DARPA has operational responsibility for the domain.}} 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]] (DNSSEC).<ref>{{Cite web | url=http://dnssec-deployment.org/pipermail/dnssec-deployment/2010-March/003730.html | archive-url=https://web.archive.org/web/20100328000016/http://dnssec-deployment.org/pipermail/dnssec-deployment/2010-March/003730.html | url-status=dead | archive-date=2010-03-28 | title=[Dnssec-deployment] Signing of the ARPA zone}}</ref>

==Subdomains==
Subdomains of ''arpa'' are created by resolution in the work groups of the Internet Engineering Task Force via the [[Request for Comments]] process, and are maintained by the [[Internet Assigned Numbers Authority]] (IANA). The DNS zone ''arpa'' has the following subdomains:<ref>{{cite web
|title=.arpa
|url=https://icannwiki.org/arpa
|publisher=[[ICANN]]
|access-date=2020-06-17
|archive-date=January 7, 2009
|archive-url=https://web.archive.org/web/20090107041018/http://icannwiki.org/ARPA
|url-status=dead
}}</ref><ref>{{cite web|title=.ARPA Zone Management|url=https://www.iana.org/domains/arpa|publisher=Internet Assigned Numbers Authority (IANA)|access-date=2023-03-02|archive-date=May 9, 2008|archive-url=https://web.archive.org/web/20080509090149/https://www.iana.org/domains/arpa|url-status=live}}</ref>
{| class=wikitable
! Domain || Purpose || Authority document ([[RFC (identifier)|RFC]])
|-
| 6tisch.arpa || For IPv6 over the [[Time Slotted Channel Hopping]] mode of [[IEEE 802.15.4]] || {{Sum RFC|9031|title=no|ref=yes}}
|-
| as112.arpa || Sinking of DNS traffic for reverse IP address resolutions, misc. (see [[Blackhole server|Blackhole server)]]|| {{Sum RFC|7535|title=no|ref=yes}}
|-
| e164.arpa || Mapping of [[E.164]] numbers to Internet [[URI]]s || {{Sum RFC|6116|title=no|ref=yes}}
|-
| eap-noob.arpa || For the Nimble Out-Of-Band authentication method of the [[Extensible Authentication Protocol]] framework || {{Sum RFC|9140|title=no|ref=yes}}
|-
| home.arpa || Residential networking || {{Sum RFC|8375|title=no|ref=yes}}
|-
| in-addr.arpa || Mapping of [[IPv4]] addresses to domain names || {{Sum RFC|1035|title=no|ref=yes}}
|-
| ip6.arpa || Mapping of [[IPv6]] addresses to domain names || {{Sum RFC|3152|title=no|ref=yes}}
|-
| in-addr-servers.arpa || rowspan=2|Domains for authoritative DNS servers for the reverse lookup domains || rowspan=2| {{Sum RFC|5855|title=no|ref=yes}}
|-
| ip6-servers.arpa
|-
| ipv4only.arpa || Detection of DNS64 availability and NAT64 prefix || {{Sum RFC|7050|title=no|ref=yes}}
|-
| iris.arpa || Locating Internet registry information services || {{Sum RFC|4698|title=no|ref=yes}}
|-
| ns.arpa || Domain for hosting authoritative DNS servers for the .arpa domain || {{Sum RFC|9120|title=no|ref=yes}}
|-
| resolver.arpa || Domain for discovery of designated DNS resolvers || {{Sum RFC|9462|title=no|ref=yes}}
|-
| service.arpa || For DNS-based service discovery over unicast || draft-ietf-dnssd-srp-25
|-
| uri.arpa || rowspan=2|Resolution of URIs and [[URN]]s,<br>according to the [[Dynamic Delegation Discovery System]] || rowspan=2| {{Sum RFC|3405|title=no|ref=yes}}
|-
| urn.arpa
|-
|}

==References==
{{Reflist}}

==External links==
* [https://www.internic.net/domain/arpa.zone arpa. zone file]

{{GTLD}}

{{DEFAULTSORT:ARPA}}
[[Category:Generic top-level domains]]
[[Category:Internet properties established in 1985]]
[[Category:1985 establishments in the United States]]