IANA is a standards organization that controls global IP address allocation, autonomous system number (ASN) allocation, Domain Name System (DNS) root zone managegement, media types (MIME type) and other Internet Protocol related symbols. Currently IANA ia a function of Internet Corporation for Assigned Names and Numbers (ICANN) organization. They delegates allocations of IP address blocks to Regional Internet Registries (RIRs).
In the Internet Protocol version 4 (IPv4), a 8-bit field called "Protocol" identifies the next level protocol.
In Internet Protocol version 6 (IPv6), a field (also 8-bit) is called the "Next Header". Next header can contain Extension Header options that are located between IPv6 header and the transport-layer header in a packet. IPv6 extension headers can have arbitrary length.