Cisco Systems, Inc. Cisco Systems, Inc. Cisco Systems, Inc. Broadcom Goldman Sachs Deutsche Telekom Colt Technology Services Path Tracing provides a record of the packet path as a sequence of interface ids. In addition, it provides a record of end-to-end delay, per-hop delay, and load on each interface that forwards the packet. Path Tracing has the lowest MTU overhead compared to alternative proposals such as [INT], [RFC9197], [I-D.song-opsawg-ifit-framework], and [I-D.kumar-ippm-ifa]. Path Tracing supports fine grained timestamp. It has been designed for linerate hardware implementation in the base pipeline. This document defines the Path Tracing specification for the SR-MPLS dataplane. The Path Tracing specification for the SRv6 dataplane is defined in [I-D.filsfils-spring-path-tracing].