Cisco Systems Cisco Systems Bell Canada CNIT Huawei Segment Routing (SR) is applicable to both Multiprotocol Label Switching (SR-MPLS) and IPv6 (SRv6) data planes. This document specifies procedures for using UDP path for sending and processing in-band probe query and response messages for Performance Measurement. The procedure uses the RFC 6374 defined mechanisms for Delay and Loss performance measurement. The procedure specified is applicable to SR-MPLS and SRv6 data planes for both links and end-to-end measurement for SR Policies. This document also defines mechanisms for handling Equal Cost Multipaths (ECMPs) for SR Policies. In addition, this document defines Return Path Segment List TLV for two-way performance measurement and Block Number TLV for loss measurement.