"The control protocol used for constructing Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths (""MP LSPs"") contains a field that identifies the address of a ""root node"". Intermediate nodes are expected to be able to look up that address in their routing tables. However@ this is not possible if the route to the root node is a BGP route and the intermediate nodes are part of a BGP-free core. This document specifies procedures that enable an MP LSP to be constructed through a BGP-free core. In these procedures@ the root node address is temporarily replaced by an address that is known to the intermediate nodes and is on the path to the true root node."
RFC 6512-2012 history
2012RFC 6512-2012 Using Multipoint LDP When the Backbone Has No Route to the Root