Segment routing (SR) is describe in RFC 8402 and offer flexible way to provide traffic engineering based on the source routing. With SR there is no longer needs to maintain a per-application and per-flow state, and traffic can obey the forwarding instruction provided in the packet.

SR relies on some extension to the routing protocols ISIS and OSPF. The SR can support any type of control plane such as distributed, centralized or hybrid.

Each control plane model provide different set of capabilities and how instructions are allocated and signaled. In a distributed scenario, the segments are allocated and signaled by IS-IS or OSPF or BGP and each node individually decides how to proceed with a packet.

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