http://www.rfc-editor.org/rfc/rfc3107.txt
RFC 3107: Carrying Label Information in BGP-4, Y. Rekhter, E. Rosen2001-05-01T23:00:00-00:00This document specifies the way in which the label mapping information for a particular route is piggybacked in the same Border Gateway Protocol (BGP) Update message that is used to distribute the route itself. [STANDARDS-TRACK]