Cisco Systems Cisco Systems Cisco Systems Orange Orange Deutsche Telekom Telekom Srbija British Telecom TDC Oy Alcatel-Lucent Ericsson Individual Contributor A Segment Routing (SR) node steers a packet through a controlled set of instructions, called segments, by prepending the packet with an SR header. A segment can represent any instruction, topological or service-based. SR allows to enforce a flow through any topological path and service chain while maintaining per-flow state only at the ingress node to the SR domain. The Segment Routing architecture can be directly applied to the MPLS data plane with no change in the forwarding plane. This drafts describes how Segment Routing operates in a network where LDP is deployed and in the case where SR-capable and non-SR-capable nodes coexist.