Registry included below
Assigned Internet Protocol Numbers
IESG Approval or Standards Action
In the Internet Protocol version 4 (IPv4) [RFC791] there is a field called "Protocol" to identify the next level protocol. This is an 8 bit field. In Internet Protocol version 6 (IPv6) [RFC8200], this field is called the "Next Header" field.
Values that are also IPv6 Extension Header Types should be listed in the IPv6 Extension Header Types registry at [IANA registry ipv6-parameters].