ARIN is one of the 5 RIRs (Regional Internet Registries) responsible for the management and distribution of the Internet number resources known as IP Addresses (IPv4 and IPv6) and ASNs. ARIN serves the region comprised of the United States, Canada, and many Caribbean and North Atlantic islands. ARIN is a nonprofit organization found in 1997. The primary function of ARIN is the registration of IP addresses and ASNs to ensure global uniqueness. Registration service includes allocation. assignment, and transfer of all Internet number resources. ARIN assigns IPv4, IPv6 and ASN numbers to governments, universities, ISPs, and for-profit organizations.

RIRs including ARIN are components of the IANA, and IANA delegates the allocation services to RIRs. IANA is the record-keeper of IP numbers and provides directory services to the public. ARIN provides directory lookup services for IP number registrations so that anyone can search the directory to determine who owns the IP numbers. The following directory services are offered:

• WhoIS lookup service to allow public to search IP address registrations.
• WhoWas historical directory is available to authorized users for IP address and ASN lookups.
• Reverse DNS delegation: ARIN enables individuals to manage their reverse delegation for IPv4 and IPv6 addresses that are assigned to them.
• Internet Routing Registry (IRR) is a searchable database of public routing policy information for networks in the ARIN region.