Backtrace Messages for Label Switched Paths
Label switched path (LSP) backtrace is a method to backtrack the paths followed by packets in a particular multi protocol label switching (MPLS) forwarding equivalence class (FEC). This document describes encoding and procedures for new label distribution protocol (LDP) messages, backtrace message and backtrace reply message used for performing LSP backtrace. Backtrace message is sent upstream for an established LSP. Backtrace message can be used for LDP LSPs as well as for constraint based label switched paths (CR-LSPs). Data requested through backtrace message is encoded into backtrace reply message. Backtrace reply message is sent in downstream direction. It always travels towards the tail end of an LSP. Backtrace mechanism described in this document can also be used for obtaining additional attributes of LSPs.