The Internet Assigned Numbers Authority, or IANA, is the function that keeps the internet’s most basic identifiers globally unique. Independently built systems can only interoperate if they agree on the meaning of certain numbers: which value identifies which protocol, which port a service listens on, which block of addresses belongs to which network. IANA is the central registry that makes those agreements possible. Its own description groups its work into three areas: management of the DNS root, coordination of IP and autonomous-system number resources, and assignment of protocol parameters.
For much of the internet’s early history, IANA was effectively one person. Jon Postel, who also edited the RFC series, personally maintained the registries of assigned numbers for nearly three decades. The reference document for these values was the “Assigned Numbers” RFC, published as RFC 1700 by Joyce Reynolds and Postel in October 1994, which states that “the Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols.” Countless protocol specifications simply pointed at IANA as the authority that would hand out the next available number.
As the internet grew and became commercially and politically significant, this informal arrangement could not continue resting on a single trusted individual. The IANA functions were moved into the newly formed Internet Corporation for Assigned Names and Numbers (ICANN), and the relationship between the IETF’s technical standards and IANA’s registries was formalized in RFC 2860, the June 2000 Memorandum of Understanding among the IETF, IAB, and ICANN. That document specifies that “IANA will assign and register Internet protocol parameters only as directed by the criteria and procedures specified in RFCs.”
The three functional areas remain distinct. Protocol parameter management keeps the many registries that IETF standards reference, from port numbers to media types to header fields. Number resource coordination allocates large blocks of IPv4 and IPv6 address space and autonomous-system numbers to the regional internet registries, which then assign them to operators. DNS root management oversees the contents and operation of the top of the domain name hierarchy, the zone from which all domain name resolution ultimately descends.
Today the IANA functions are delivered through Public Technical Identifiers, an affiliate of ICANN, under arrangements that grew out of the 2016 transition of stewardship away from direct U.S. government oversight. But the essential job has not changed since Postel kept it in a set of files: somebody has to hold the master lists, so that every machine on the internet can agree on what the numbers mean.