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+.. _srv6_doc:
+
+SRv6: Segment Routing for IPv6
+==============================
+
+This is a memo intended to contain documentation of the VPP SRv6
+implementation. Everything that is not directly obvious should come
+here. For any feedback on content that should be explained please
+mailto:pcamaril@cisco.com
+
+Segment Routing
+---------------
+
+Segment routing is a network technology focused on addressing the
+limitations of existing IP and Multiprotocol Label Switching (MPLS)
+networks in terms of simplicity, scale, and ease of operation. It is a
+foundation for application engineered routing as it prepares the
+networks for new business models where applications can control the
+network behavior.
+
+Segment routing seeks the right balance between distributed intelligence
+and centralized optimization and programming. It was built for the
+software-defined networking (SDN) era.
+
+Segment routing enhances packet forwarding behavior by enabling a
+network to transport unicast packets through a specific forwarding path,
+different from the normal path that a packet usually takes (IGP shortest
+path or BGP best path). This capability benefits many use cases, and one
+can build those specific paths based on application requirements.
+
+Segment routing uses the source routing paradigm. A node, usually a
+router but also a switch, a trusted server, or a virtual forwarder
+running on a hypervisor, steers a packet through an ordered list of
+instructions, called segments. A segment can represent any instruction,
+topological or service-based. A segment can have a local semantic to a
+segment-routing node or global within a segment-routing network. Segment
+routing allows an operator to enforce a flow through any topological
+path and service chain while maintaining per-flow state only at the
+ingress node to the segment-routing network. Segment routing also
+supports equal-cost multipath (ECMP) by design.
+
+Segment routing can operate with either an MPLS or an IPv6 data plane.
+All the currently available MPLS services, such as Layer 3 VPN (L3VPN),
+L2VPN (Virtual Private Wire Service [VPWS], Virtual Private LAN Services
+[VPLS], Ethernet VPN [E-VPN], and Provider Backbone Bridging Ethernet
+VPN [PBB-EVPN]), can run on top of a segment-routing transport network.
+
+**The implementation of Segment Routing in VPP covers both the IPv6 data
+plane (SRv6) as well as the MPLS data plane (SR-MPLS). This page
+contains the SRv6 documentation.**
+
+Segment Routing terminology
+---------------------------
+
+-  Segment Routing Header (SRH): IPv6 routing extension header of type
+   ‘Segment Routing’. (draft-ietf-6man-segment-routing-header-05)
+-  SegmentID (SID): is an IPv6 address.
+-  Segment List (SL) (SID List): is the sequence of SIDs that the packet
+   will traverse.
+-  SR Policy: defines the SRH that will be applied to a packet. A packet
+   steered into an SR policy may either receive the SRH by IPv6 header
+   encapsulation (as recommended in draft-ietf-6man-rfc2460bis) or it
+   could be inserted within an existing IPv6 header. An SR policy is
+   uniquely identified by its Binding SID and associated with a weighted
+   set of Segment Lists. In case several SID lists are defined, traffic
+   steered into the policy is unevenly load-balanced among them
+   according to their respective weights.
+-  Local SID: is a SID associated with a processing function on the
+   local node, which may go from advancing to the next SID in the SRH,
+   to complex user-defined behaviors. When a FIB lookup, either in the
+   main FIB or in a specific VRF, returns a match on a local SID, the
+   associated function is performed.
+-  BindingSID: a BindingSID is a SID (only one) associated one-one with
+   an SR Policy. If a packet arrives with an IPv6 DA corresponding to a
+   BindingSID, then the SR policy will be applied to such packet.
+
+SRv6 Features in VPP
+--------------------
+
+The SRv6 Network Programming
+(*draft-filsfils-spring-srv6-network-programming*) defines the SRv6
+architecture.
+
+VPP supports the following SRv6 LocalSID functions: End, End.X, End.DX6,
+End.DT6, End.DX4, End.DT4, End.DX2, End.B6, End.B6.Encaps.
+
+For further information and how to configure each specific function:
+:ref:`srv6_localsid_doc`
+
+The Segment Routing Policy
+(*draft-filsfils-spring-segment-routing-policy*) defines SR Policies.
+
+VPP supports SRv6 Policies with T.Insert and T.Encaps behaviors.
+
+For further information on how to create SR Policies: :ref:`srv6_policy_doc`
+
+For further information on how to steer traffic into SR Policies:
+:ref:`srv6_steering_doc`
+
+SRv6 LocalSID development framework
+-----------------------------------
+
+One of the *‘key’* concepts about SRv6 is network programmability. This
+is why an SRv6 LocalSID is associated with an specific function.
+
+However, the true way to enable network programmability is allowing
+any developer **easily** create his own SRv6 LocalSID function. That is
+the reason why we have added some API calls such that any developer can
+code his own SRv6 LocalSID behaviors as plugins an add them to the
+running SRv6 code.
+
+The principle is that the developer only codes the behavior -the graph
+node-. However all the FIB handling, SR LocalSID instantiation and so on
+are done by the VPP SRv6 code.
+
+For more information please refer to: :ref:`srv6_plugin_doc`
+
+Available SRv6 plugins include:
+
+-  :ref:`srv6_as_plugin_doc`
+-  :ref:`srv6_ad_plugin_doc`
+-  :ref:`srv6_am_plugin_doc`
+-  :ref:`srv6_mobile_plugin_doc`