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BGP Link-State extensions for Segment Routing

BGP Link-State extensions for Segment Routing. Hannes Gredler Saikat Ray Stefano Previdi Clarence Filsfils Mach( Guoyi ) Chen Jeff Tantsura. Introduction. Segment routing A flexible, scalable way of doing source routing Segments are “instructions”

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BGP Link-State extensions for Segment Routing

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  1. BGP Link-State extensions for Segment Routing Hannes Gredler Saikat Ray Stefano Previdi Clarence Filsfils Mach(Guoyi) Chen Jeff Tantsura

  2. Introduction • Segment routing • A flexible, scalable way of doing source routing • Segments are “instructions” • “Go to node N via shortest path”, “use link L”, etc. • Each segment is identified by a “Segment ID” (SID) • IGPs advertise the <Segments, SID> • Ingress node adds SID stack to data packets to determine the packet path • Per-flow state is only at the ingress node • SIDs map to MPLS labels for MPLS data plane

  3. Need for BGP LS +------------+ | Consumer | +------------+ ^ | v +-------------------+ | BGP Speaker | +-----------+ | (Route-Reflector) | | Consumer | +-------------------+ +-----------+ ^ ^ ^ ^ | | | | +---------------+ | +-------------------+ | | | | | v vvv +-----------+ +-----------+ +-----------+ | BGP | | BGP | | BGP | | Speaker | | Speaker | . . . | Speaker | +-----------+ +-----------+ +-----------+ ^ ^ ^ | | | IGP IGPIGP • Segments are used to set up end-to-end paths (topological and services) • Paths may span IGP areas, or even ASes • Segment information from one IGP area alone does not work • BGP LS collects LSDB from all IGP areas • BGP LS provides visibility into segment information required for building end-to-end paths

  4. BGP LS • BGP LS models the IGP network as a collection of three types of objects: (i) Nodes, (ii) Links (ordered pair of nodes) and (iii) Prefixes • Each object is encoded as BGP object • The “key” portion of the objects is the NLRI • The rest of the properties of the object are in the BGP-LS attribute • BGP-LS attribute is a set of TLVs; easily extended • Approach: Add the segment information in the BGP-LS attribute of the corresponding object

  5. Segment routing TLVs • SR information TLVs are defined in I-D.previdi-isis-segment-routing-extensions • TLV for Prefix-SID • TLV for Adjacency-SID between two nodes as well as between nodes in a LAN • TLV for SID/Label binding for advertising paths from other protocols (and their optional ERO) • TLV for SR Capabilities • TLV for SR Algorithm • Encoding Defined in this draft 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // Value (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ From IS-IS

  6. SR TLVs in Node Attribute • The following SR TLVs are in the node attribute (BGP-LS attribute that is added to a node NLRI) +---------------+-------------------+----------+--------------------+ | TLV Code | Description | Length | IS-IS SR | | Point | | | TLV/sub-TLV | +---------------+-------------------+----------+--------------------+ | 1033 | SID/Label Binding | variable | 149 | | 1034 | SR Capabilities | variable | 2 | | 1035 | SR Algorithm | variable | 15 | +---------------+-------------------+----------+--------------------+

  7. SR TLVs in Link Attribute • The following TLVs are added to a link attribute +-----------+----------------------------+----------+---------------+ | TLV Code | Description | Length | IS-IS SR | | Point | | | TLV/sub-TLV | +-----------+----------------------------+----------+---------------+ | 1099 | Adjacency Segment | variable | 31 | | | Identifier (Adj-SID) TLV | | | | 1100 | LAN Adjacency Segment | variable | 32 | | | Identifier (Adj-SID) TLV | | | +-----------+----------------------------+----------+---------------+

  8. SR TLVs in Prefix Attribute • The following TLVs are added to a Prefix attribute +----------------+-------------+----------+----------------------+ | TLV Code Point | Description | Length | IS-IS SR TLV/sub-TLV | +----------------+-------------+----------+----------------------+ | 1158 | Prefix SID | variable | 3 | +----------------+-------------+----------+----------------------+

  9. What next • WG document • Add more details on SID/label binding TLV • Prototype implementations

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