Infrastructure

Infrastructure top-level domains serve critical technical functions in the domain name system itself. The only infrastructure TLD currently in use is .arpa (Address and Routing Parameter Area), which is managed directly by the Internet Architecture Board (IAB) and IANA. The .arpa domain is essential for reverse DNS lookups: when you query the IP address 192.0.2.1, the DNS system looks up 1.2.0.192.in-addr.arpa to find the associated hostname. This process is fundamental to email authentication (SPF, DKIM), network diagnostics, and security auditing. The .arpa TLD also hosts other infrastructure zones including ip6.arpa for IPv6 reverse lookups and e164.arpa for telephone number mapping (ENUM). Unlike other TLDs, .arpa is not available for public registration — it exists solely to support the internet's core addressing infrastructure.