Description: The reason why the session transitioned from operational to nonexistent state. Can be one of the following: unknown reason, hold time expired, connection time expired, all adjacencies down, received bad tlv, received bad pdu, connection error, connection reset, received notification from peer, received unexpected end-of-file, clear mpls ldp, error during initialization, graceful restart was aborted or client command. If no such changes have occurred since the last re-initialization of the local management subsystem, then this object contains a zero value.