Cisco Systems, Inc. Cisco Systems, Inc. ZTE Corporation Huawei Technologies Nokia The Algorithm associated with a prefix Segment-ID (SID) defines the path computation Algorithm used by Interior Gateway Protocols (IGPs). This information is available to controllers such as the Path Computation Element (PCE) via topology learning. This document proposes an approach for informing headend routers regarding the Algorithm associated with each prefix SID used in PCE-computed paths, as well as signalling a specific SR algorithm as a constraint to the PCE.