Huawei Huawei Huawei Segment routing (SR) leverages the source routing mechanism. It allows for a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological sub-paths which are called segments. These segments are advertised by the link-state routing protocols (IS-IS and OSPF). Unlike the MPLS, SR does not have the specific path construction signaling so that it cannot support the Path MTU. This draft provides the necessary IS-IS and OSPF extensions about the Path MTU that need to be used on SR. Here, the term "OSPF" means both OSPFv2 and OSPFv3.