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| Introduced | January 1, 1985 |
|---|---|
| TLD type | Infrastructure domain |
| Status | Active |
| Registry | IANA |
| Sponsor | Internet Architecture Board |
| Intended use | A temporary TLD to facilitate the transition from ARPANET to the DNS. |
| Actual use | Internet infrastructure such as reverse DNS lookup. |
| Registration 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. |
| Documents | RFC 3172; RFC 9120 |
| Dispute policies | None |
| DNSSEC | Yes |
| Registry website | IANA .arpa info |
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.