http://www.rfc-editor.org/rfc/rfc4379.txt
RFC 4379: Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures, K. Kompella, G. Swallow2006-02-01T23:00:00-00:00This document describes a simple and efficient mechanism that can be used to detect data plane failures in Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs). There are two parts to this document: information carried in an MPLS "echo request" and "echo reply" for the purposes of fault detection and isolation, and mechanisms for reliably sending the echo reply. [STANDARDS-TRACK]