.arpa

The domain name .arpa is a top-level domain (TLD) in the Domain Name System. It is used exclusively for technical infrastructure purposes. While the name originally was the acronym for the Advanced Research Projects Agency (ARPA), the funding organization in the United States that developed the precursor of the Internet (ARPANET), it now stands for Address and Routing Parameter Area.

.Arpa contains six subdomains, including the reverse domain name resolution domains in-addr.arpa and ip6.arpa for IPv4 and IPv6, respectively.