Cisco Systems, Inc. Cisco Systems, Inc. Verizon Wireless ZTE Corp. This document specifies encapsulations for the Simple Two-Way Active Measurement Protocol (STAMP), defined in RFC 8762, and its optional extensions, defined in RFC 8972, in MPLS networks. It specifies the encapsulation of STAMP test packets for point-to-point Label Switched Paths (LSPs) and point-to-point single-segment Pseudowires (PWs), with or without an IP/UDP header, so that the test packets experience the same forwarding and Equal-Cost Multi-Path (ECMP) behavior as the data traffic being measured. In addition, two new MPLS Generic Associated Channel (G-ACh) types are defined. This document updates RFC 8762 and RFC 8972 to allow STAMP to operate without an IP/UDP header when STAMP test packets are carried over MPLS LSPs and PWs, and specifies the resulting changes to the processing of the STAMP session identifier, the TTL and IPv6 Hop Limit, and the STAMP TLV extensions. This document specifies the requirements for IPv6 STAMP in unauthenticated mode using UDP zero-checksum, which deviates from the integrity requirement in RFC 6936.