US Patent 7990888 System and methods for network reachability detection

A mechanism for ASBRs to identify the originating node, or router, in an LSP conversant autonomous system (AS), such as an MPLS VPN environment, maintains the identity of the originating node and successive nodes in subsequent autonomous systems along the path to the node to be pinged. The identity of the transporting nodes is stored in a stack or other object associated with the ping request (ping), such that the pinged node may employ the stored identity as a set of return path routing information. Successive ASBRs store their identity on the stack, in an ordered manner, along the path to the destination. Upon reaching the destination (ping) node, the destination node employs the identity of the first node on the stack to send the acknowledgment, or ping response. Each successive ASBR, therefore, pops (retrieves) the next node identity from the stack and redirects (sends) the ping response to the retrieved node.