Contains technical and organizational documents about the Internet, including the technical specifications and policy documents produced by the Internet Engineering Task Force (IETF)."
RFCs are subject to detailed licensing terms as documented by the RFC editor. It appears that some rights are reserved, so that they are not public domain. The "boiler-plate" copyright details required for all RFCs can be found on the submission page.
It appears that RFCs start with a "Status of this memo" section which includes "Distribution of this memo is unlimited". However, this is not mentioned in the discussion of copyright bolier-plate.