http://www.rfc-editor.org/rfc/rfc6720.txt
RFC 6720: The Generalized TTL Security Mechanism (GTSM) for the Label Distribution Protocol (LDP), C. Pignataro, R. Asati2012-08-01T23:00:00-00:00This specification uses a bit reserved in RFC 5036 and therefore updates RFC 5036. [STANDARDS-TRACK]