Segment routing, a form of computer networking, is a modern variant of source routing that is being developed within the SPRING and IPv6 working groups of the IETF. In a segment routed network, an ingress node may prepend a header to packets that contain a list of segments, which are instructions that are executed on subsequent nodes in the network. These instructions may be forwarding instructions, such as an instruction to forward a packet to a specific destination or interface.
Segment routing works either on top of a MPLS network or on an IPv6 network.[1] [2] In an MPLS network, segments are encoded as MPLS labels. Under IPv6, a new header called a Segment Routing Header (SRH) is used. Segments in a SRH are encoded in a list of IPv6 addresses. The 5f00::/16 prefix has been allocated for this purpose as part of an Internet-Draft.[3]