Internet DRAFT - draft-lin-pce-srv6-segment-list-optimize

draft-lin-pce-srv6-segment-list-optimize



PCE Working Group                                                C. Lin
Internet-Draft                                     New H3C Technologies
Intended status: Standards Track                                 Y. Liu
Expires: July 5, 2024                                      China Mobile
                                                                R. Chen
                                                                    ZTE
                                                                 Y. Qiu
                                                   New H3C Technologies
                                                        January 5, 2024



          PCEP Extension to Support SRv6 Segment List optimization
                draft-lin-pce-srv6-segment-list-optimize-01


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   respect to this document. Code Components extracted from this
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Abstract

   The Path Computation Element Communication Protocol (PCEP) provides
   mechanisms for Path Computation Elements (PCEs) to perform path
   computations in response to Path Computation Clients (PCCs) requests.
   Segment routing (SR) leverages the source routing and tunneling
   paradigms. The Stateful PCEP extensions allow stateful control of
   Segment Routing Traffic Engineering (TE) Paths.  Furthermore, PCEP
   can be used for computing SR TE paths in the network.

   This document defines PCEP extensions for optimizing the arrangement
   of segment lists to solve the problem of the penultimate segment
   node being unable to perform PSP behavior when the egress node has
   both End SID and service SID, and improve the forwarding efficiency
   of data packets.

Table of Contents


   1. Introduction ................................................ 3
   2. Terminology ................................................. 3
   3. Requirement Background ...................................... 4
   4. Extend the Flags of SRv6-ERO subobject ...................... 4
   5. Operation ................................................... 5
   6. IANA Considerations ......................................... 5
   7. Security Considerations ..................................... 5
   8. References .................................................. 6
      8.1. Normative References ................................... 6
      8.2. Informative References ................................. 7
   9. Acknowledgments ............................................. 7
   Authors' Addresses ............................................. 7













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   1. Introduction

   Segment Routing (SR) [RFC8402] allows a headend node to steer a
   packet flow along any path. Intermediate per-path states are
   eliminated thanks to source routing.

   The headend node is said to steer a flow into an SR Policy [RFC8402].
   The packets steered into an SR Policy carry an ordered list of
   segments associated with that SR Policy.

   The Path Computation Element Communication Protocol (PCEP) provides
   mechanisms for Path Computation Elements (PCEs) to perform path
   computations in response to Path Computation Clients (PCCs) requests.
   The Stateful PCEP extensions allow stateful control of Segment
   Routing Traffic Engineering (TE) Paths.

   [I-D.ietf-pce-segment-routing-ipv6] provides a mechanism for a
   network controller (acting as a PCE) to instantiate candidate paths
   for an SR Policy onto a head-end node (acting as a PCC) using PCEP.

   This document defines PCEP extensions for optimizing the arrangement
   of segment lists to solve the problem of the penultimate segment
   node being unable to perform PSP behavior when the egress node has
   both End SID and service SID, and improve the forwarding efficiency
   of data packets.

   2. Terminology

   The following terminologies are used in this document.

   SR: Segment Routing

   SRv6: SR for IPv6

   SRH: Segment Routing Header

   SID: Segment Identifier

   CE: Customer Edge

   PE: Provider Edge

   VPN: Virtual Private Network

   PSP: Penultimate Segment Pop

   PCEP: Path Computation Element Communication Protocol


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   PCE: Path Computation Element

   PCC: Path Computation Client

   3. Requirement Background

   The requirement background of optimizing the arrangement of segment
   lists is specified in [I-D.liu-idr-srv6-segment-list-optimize].

   When instantiating the candidate path of SRv6 Policy to the ingress
   node via PCEP, it is also necessary to inform the ingress node which
   is the egress node's SID.

   After the head node receives the PCEP message, when the SID is used
   as the egress node's SID of the SRv6 forwarding path, if
   SRH.SegmentList already contains the service SID of the egress node,
   the egress node's SID will not be encapsulated at the same time.

   4. Extend the Flags of SRv6-ERO subobject

   Extend the Flags of the SRv6-ERO subobject defined in [I-D.ietf-pce-
   segment-routing-ipv6]. Define a E bit to identify which is the
   egress node's SID.

   The format of SRv6 ERO after adding E bit is as follows:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |L|   Type=40   |     Length    | NT    |     Flags   |E|V|T|F|S|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Reserved         |      Endpoint Behavior        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                  SRv6 SID (optional)                          |
   |                     (128-bit)                                 |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                    NAI (variable, optional)                 //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     SID Structure (optional)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

         E-Flag: This flag, when set, indicates that this segment is
   the egress node's SID.


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   If the SRH.SegmentList of the packet already contains the service
   SID of the egress node, the End SID of the egress node will not be
   encapsulated in the segment list at the same time.

   5. Operation

   After the controller arranges the SRv6 forwarding path, it informs
   the ingress node which is the egress node's SID through the E-Flag.

   When the controller distributes the SRv6 Policy configuration to the
   head node through PCEP, the E bit of Flags field of the SRv6-ERO
   Subobject corresponding to the egress node is set to 1. And the E-
   Flag bits corresponding to the ingress node and intermediate node
   are set to 0.

   After receiving the SRv6 Policy configuration with E bit set to 1,
   the ingress node will not simultaneously arrange the End SID and
   Service SID of the egress node into the SRH.SegmentList of packet.

   For data packets forwarded to VPN through this SRv6 Policy, the
   SRH.SegmentList will not encapsulate the End SID corresponding to
   the egress node in the SID list of SRv6 Policy.

   If the forwarding path does not include the service SID of the
   egress node, then the End SID of the egress node should be
   encapsulated in SRH.SegmentList.

   For the OAM detection message of this SRv6 Policy, all node SIDs of
   the SID lists will be encapsulated.

   6. IANA Considerations

   This document requests that IANA allocate the following registration
   in the "SRv6-ERO Flag Field" sub-registry for the "Path Computation
   Element Protocol (PCEP) Numbers" registry maintained by IANA:

    +-------+-------------------------------------+---------------+
    | Bit   | Description                         | Reference     |
    +=======+=====================================+===============+
    | TBA   | Indication of egress node's SID (E) | This document |
    +-------+-------------------------------------+---------------+

   7. Security Considerations

   [RFC8754] defines the notion of an SR domain and use of SRH within
   the SR domain. Procedures for securing an SR domain are defined the
   section 5.1 and section 7 of [RFC8754].

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   This document does not impose any additional security challenges to
   be considered beyond security threats described in [RFC8754],
   [RFC8679] and [RFC8986].

   8. References

   8.1. Normative References

   [I-D.ietf-pce-segment-routing-ipv6] Li, C., Negi, M., Sivabalan, S.,
             Koldychev, M., Kaladharan, P., Zhu, Y., "Path Computation
             Element Communication Protocol (PCEP) Extensions for
             Segment Routing leveraging the IPv6 dataplane", draft-
             ietf-pce-segment-routing-ipv6-20 (work in progress),
             September 2023.

   [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
             Decraene, B., Litkowski, S., and R. Shakir, "Segment
             Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
             July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [RFC8679] Shen, Y., Jeganathan, M., Decraene, B., Gredler, H.,
             Michel, C., and H. Chen, "MPLS Egress Protection
             Framework", RFC 8679, DOI 10.17487/RFC8679, December 2019,
             <https://www.rfc-editor.org/info/rfc8679>.

   [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
             Matsushima, S., and D. Voyer, "IPv6 Segment Routing
             Header(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
             <https://www.rfc-editor.org/info/rfc8754>.

   [RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
             D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
             (SRv6) Network Programming", RFC 8986, DOI
             10.17487/RFC8986, February 2021, <https://www.rfc-
             editor.org/info/rfc8986>.













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   8.2. Informative References

   TBD

   9. Acknowledgments

   TBD

Authors' Addresses

   Changwang Lin
   New H3C Technologies

   Email: linchangwang.04414@h3c.com

   Yisong Liu
   China Mobile

   Email: liuyisong@chinamobile.com

   Ran Chen
   ZTE Corporation

   Email: chen.ran@zte.com.cn

   Yuanxiang Qiu
   New H3C Technologies

   Email: qiuyuanxiang@h3c.com



















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