http://www.rfc-editor.org/rfc/rfc5496.txt
RFC 5496: The Reverse Path Forwarding (RPF) Vector TLV, IJ. Wijnands, A. Boers, E. Rosen2009-03-01T23:00:00-00:00This document describes a use of the Protocol Independent Multicast (PIM) Join Attribute as defined in RFC 5384, which enables PIM to build multicast trees through an MPLS-enabled network, even if that network's IGP does not have a route to the source of the tree. [STANDARDS-TRACK]