SegmentRoutingHeader

Segment Routing Header, often abbreviated as SRH, is an extension to the IPv6 header that enables Segment Routing. Segment Routing is a traffic engineering technique that simplifies network core and edge device functions by pushing the routing intelligence to the source. The SRH allows a source to specify an ordered list of network segments, called a segment list, that the packet must traverse. Each segment in the list represents a node or a link in the network. The SRH carries this segment list, and the network forwards the packet based on the instructions within the header.

The SRH is identified by a specific Next Header value in the IPv6 header. It contains fields such as the Segment Routing Type, the first segment in the segment list, and a variable-length list of segments. As the packet traverses the network, the egress node of each segment pops the current segment and forwards the packet to the next segment in the list. This allows for explicit path control, traffic engineering, and simplified network device configurations. SRH is a key component in enabling Software-Defined Networking (SDN) and Network Function Virtualization (NFV) by providing a flexible and programmable way to steer traffic through the network. It is standardized by the Internet Engineering Task Force (IETF).