New Host-Host Protocol
RFC 33, “New Host-Host Protocol”, is an Unknown document published in February 1970 by S.D. Crocker. It obsoletes RFC 11. It has since been updated by RFC 36, RFC 47. The canonical text is published by the RFC Editor.
What “Unknown” means
The standards-track status of this early RFC was never formally classified.
The canonical text of RFC 33 is hosted at rfc-editor.org. Available in TXT,HTML.