http://www.rfc-editor.org/rfc/rfc4684.txt
RFC 4684: Constrained Route Distribution for Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual Private Networks (VPNs), P. Marques, R. Bonica, L. Fang, L. Martini, R. Raszuk, K. Patel, J. Guichard2006-11-01T23:00:00-00:00This document defines Multi-Protocol BGP (MP-BGP) procedures that allow BGP speakers to exchange Route Target reachability information. This information can be used to build a route distribution graph in order to limit the propagation of Virtual Private Network (VPN) Network Layer Reachability Information (NLRI) between different autonomous systems or distinct clusters of the same autonomous system. This document updates RFC 4364. [STANDARDS-TRACK]