http://www.rfc-editor.org/rfc/rfc6563.txt
RFC 6563: Moving A6 to Historic Status, S. Jiang, D. Conrad, B. Carpenter2012-03-01T23:00:00-00:00This document provides a summary of issues related to the use of A6 records, discusses the current status, and moves RFC 2874 to Historic status, providing clarity to implementers and operators. This document is not an Internet Standards Track specification; it is published for informational purposes.