Editing .arpa (section)

==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>.