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Versions: 00 03

PCE                                                             Q. Xiong
Internet-Draft                                                   S. Peng
Intended status: Standards Track                         ZTE Corporation
Expires: November 12, 2020                                  May 11, 2020


                  PCEP Extension for SRv6 Unified SIDs
           draft-xiong-pce-segment-routing-ipv6-complement-03

Abstract

   This document proposes PCEP extensions for SRv6 Path which applied to
   the use of SRv6 Unified SIDs.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on November 12, 2020.

Copyright Notice

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  PCEP Extensions for SRv6 Unified SIDs . . . . . . . . . . . .   3
     3.1.  The OPEN Object . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  The LSP Object  . . . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  The UNIFIED-SID-INFO TLV  . . . . . . . . . . . . . .   6
     3.3.  The ERO Object  . . . . . . . . . . . . . . . . . . . . .   6
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  New SR PCE Capability Flag Registry . . . . . . . . . . .   8
     7.2.  New LSP Flag Registry . . . . . . . . . . . . . . . . . .   8
     7.3.  Extension for SRv6-ERO Registry . . . . . . . . . . . . .   8
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   [RFC5440] describes the Path Computation Element Protocol (PCEP)
   which is used between a Path Computation Element (PCE) and a Path
   Computation Client (PCC) (or other PCE) to enable computation of
   Multi-protocol Label Switching (MPLS) for Traffic Engineering Label
   Switched Path (TE LSP).  PCEP Extensions for the Stateful PCE Model
   [RFC8231] describes a set of extensions to PCEP to enable active
   control of MPLS-TE and Generalized MPLS (GMPLS) tunnels.  [RFC8281]
   describes the setup and teardown of PCE-initiated LSPs under the
   active stateful PCE model, without the need for local configuration
   on the PCC, thus allowing for dynamic centralized control of a
   network.

   Segment Routing (SR) leverages the source routing paradigm.  Segment
   Routing can be instantiated on MPLS data plane which is referred to
   as SR-MPLS [RFC8660].  SR-MPLS leverages the MPLS label stack to
   construct the SR path.  PCEP Extensions for Segment Routing [RFC8664]
   specifies extensions to the PCEP that allow a stateful PCE to compute
   and initiate TE paths in SR networks.  Segment Routing can be applied
   to the IPv6 architecture which is called SRv6 with the Segment
   Routing Header (SRH) [RFC8754].  [I-D.ietf-pce-segment-routing-ipv6]
   extends the PCEP to support SRv6.

   [I-D.ietf-spring-srv6-network-programming] proposes the SRv6 Network
   Programming to specify a packet processing program by encoding a
   sequence of instructions in the IPv6 packet header.  It defined the



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   SID as two parts, LOC:FUNCT or a complete structure is
   BLOCK:NODE:FUNCT:ARGS.  However, the size of SRv6 SID faces a scaling
   challenge to use topological instructions.
   [I-D.mirsky-6man-unified-id-sr] proposed an extension of SRH that
   enables the use of unified segment identifiers which is referred to
   as unified SID, such as MPLS label or IPv4 address, to compress the
   SRH.  So the controller (i.e.  PCE) should indicate the SRv6 path
   with SRv6 unified SIDs in a 128-bit classic SRv6 SID.
   [I-D.liu-idr-segment-routing-te-policy-complement] defined the BGP
   extensions to advertise Unified SIDs in SR-TE policies.

   This document proposes PCEP extensions for SRv6 Path which applied to
   the use of SRv6 Unified SIDs.

2.  Conventions used in this document

2.1.  Terminology

   The terminology is defined as [RFC5440], [RFC8660],
   [I-D.ietf-spring-srv6-network-programming] and
   [I-D.ietf-pce-segment-routing-ipv6].

2.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  PCEP Extensions for SRv6 Unified SIDs

   As defined in [I-D.mirsky-6man-unified-id-sr], the unified SID is
   used to compress the SRH, and a new field Size (two-bits) in the SRH
   Flags field is defined as UET (U-SID Encapsulation Type) which is
   used to indicate which UET domain the packet is currently in.
   Especially for UET 0b01 domain, the SIDs which allocated by SRv6
   nodes are in the same SRv6 SID Locator Block, SRH only needs to store
   the difference between SIDs, such as NODE:FUNCT:ARGS.  The 128-bits
   SRv6 SID can be compressed and truncated and does not need to contain
   the SRv6 SID Locator Block information but the truncated information.
   The length of SRv6 SID Locator Block (BL) and the length of truncated
   SRv6 SID (TL) in a 128-bits classic SRv6 SID should be advertised
   with each SID from PCE to PCC.

   An SR path that can be optimized by short U-SIDs and the 128-bit SID
   can be compressed to a truncated SID.  To verify the TL of the SID, a
   PCE may collect U-SID encapsulation capability (UEC) information and



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   SID allocation per UET flavor of all SRv6 nodes.  Each node can
   support one or more UEC in SRv6 networks.  A border node may belong
   to multiple UET domains, so it may support more than one UEC.  If a
   node support an UEC, it should also allocate related SIDs for this
   UET flavor.  For a SID with specific UET flavor allocated by a node,
   from the perspective of this node, it starts a specific UET domain.
   When a PCE computes an SRv6 path, it can check the UEC of each node
   along this path and outline which UET domain the SRv6 path crosses.
   The UET flavor attribute may be advertised with each SID by PCE to
   indicate the type of UET domain which the next segment node belongs
   to.  The PCC should optimize each original 128-bits SID to a short
   one (e.g, 32-bits) along the path and verify the result according to
   the UET flavor of previous SID.

   The UET flavor attribute and BL and TL information of each SID can be
   directly obtained from the link-state database that is used for path
   computation by PCE.  So when a PCE is used to support path
   computation in SRv6 networks, the capability of SRv6 path with
   unified SIDs should be advertised between the PCE and PCC.  The
   information of BL, TL and UET with a 128-bit classic SRv6 SID should
   be configured from PCE to PCC.

3.1.  The OPEN Object

   When the PCEP is used to support path computation in SRv6 networks,
   the capability of SRv6 path with unified SIDs should be advertised
   between the PCE and PCC.

   As defined in [I-D.ietf-pce-segment-routing-ipv6], PCEP speakers use
   SRv6 PCE Capability sub-TLV to exchange information about their SRv6
   capability carried in Open object.  This document defined a new flag
   (U-flag) for SRv6 PCE Capability sub-TLV as shown in Figure 1.



















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       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=TBD1          |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Reserved           |             Flags       |U|N|X|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   MSD-Type    | MSD-Value     |   MSD-Type    | MSD-Value     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                             ...                             //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   MSD-Type    | MSD-Value     |           Padding             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


              Figure 1: U-flag in SRv6-PCE-CAPABILITY sub-TLV

   U (SRv6 unified SIDs is supported) : A PCE sets this flag bit to 1
   carried in Open message to indicate that it supports the
   configuration of SRv6 path with unified SIDs.  A PCC sets this flag
   to 1 to indicate that it supports the capability of processing the
   unified SIDs and and supports the results of SRv6 path with unified
   SIDs.

3.2.  The LSP Object

   The LSP Object is defined in Section 7.3 of [RFC8231].  This document
   defiend a new flag (U-flag) for the LSP Object as Figure 2 shown:


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                PLSP-ID                |        Flag         |U|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                        TLVs                                 //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                      Figure 2: U-flag in LSP Object

   U (SRv6 Unified SIDs bit) : If the bit is set to 1, it indicates that
   the PCC requests PCE to compute the SRv6 path with the unified SIDs
   information.  A PCE would set this bit to 1 and include a UNIFIED-
   SID-INFO TLV in the LSP object to configure the SRv6 unified SIDs
   information in the PCEP message.




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3.2.1.  The UNIFIED-SID-INFO TLV

   The UNIFIED-SID-INFO TLV is an optional TLV for use in the LSP Object
   for SRv6 path computation.  The type of this TLV is to be allocated
   by IANA.  The format is as shown below.


       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Reserved                        |FSU|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                 Figure 3: The UNIFIED-SID-INFO TLV Format

   FSU (First SID UET-domain flag, 2bits), indicates the first UET
   domain constructed by the headend and the first segment node.  The
   value as per [I-D.mirsky-6man-unified-id-sr].

3.3.  The ERO Object

   SRv6-ERO subobject is used for SRv6 path which consists of one or
   more SRv6 SIDs as defined in [I-D.ietf-pce-segment-routing-ipv6].
   This document extends the SRv6-ERO for supporting the SRv6 unified
   SIDs as Figure 2 shown:

          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=TBD3  |     Length    | NT    |     Flags     |UET|F|S|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Block Len  | Truncated Len |        Function Code          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                      SRv6 SID (optional)                      |
       |                     (128-bit)                                 |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //                    NAI (variable, optional)                 //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                Figure 4: Extension for SRv6-ERO Subobject





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   UET (U-SID Encapsulation Type, 2bits), indicates the UET domain
   constructed by the current segment node and the next segment node.
   The value as per [I-D.mirsky-6man-unified-id-sr].  Especially, the
   UET-flag of the last SID will determine whether the overlay VPN SID
   can be optimized or not in SRH.

   Block Len (BL, 8bits), indicates the bit length of SRv6 SID Locator
   Block information of a 128-bit SID.  The value range is [1~128].  If
   the SID is MPLS label, the value of BL is set to 0.

   Truncated Len (TL, 8bits), indicates the bit length of SRv6 SID
   Locator Truncated SID information of a 128-bit SID.  The value range
   is [1~128].  It is the length of the Node:Func:ARGs which is
   immediately followed the SRv6 SID Locator Block.  For example, if the
   128-bit SID is truncated to 32 bits, the TL is set to 32.  And if it
   is 128-bit SID and not be truncated, the TL is set to 128.  If the
   SID is MPLS label, the value of TL is set to 32.

4.  Operations

   The PCC and PCE exchanges the capability of supporting SRv6
   compresses SIDs with U bit set to 1 with in SRv6 PCE Capability sub-
   TLV carried in Open message.  The SRv6 path is initiated by PCE or
   PCC with PCReq, PCInitiated or PCUpd messages.

   When PCC received the SRv6 path, if the U-Flag in the LSP object is
   set to 1, the SRv6 path could be optimized to an SID list that
   contains short U-SIDs.

   For each original SID in SRv6-ERO subobject, it will be optimized to
   an U-SID with the help of BL and TL field and verified according to
   the UET of prev SID.  Especially, the original first SID could be
   verified with a short U-SID according the FSU flag within UNIFIED-
   SID-INFO TLV.

   The SRH will contain the optimized U-SIDs, and the initial UET of SRH
   will be set as FSU.  Other procedures refer to
   [I-D.mirsky-6man-unified-id-sr].

5.  Security Considerations

   TBA

6.  Acknowledgements

   TBA





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7.  IANA Considerations

7.1.  New SR PCE Capability Flag Registry

   SR PCE Capability TLV is defined in
   [I-D.ietf-pce-segment-routing-ipv6], and the registry to manage the
   Flag field of the SRv6 PCE Capability TLV is requested in
   [I-D.ietf-pce-segment-routing-ipv6].  IANA is requested to make
   allocations from the registry, as follows:

   +--------+-----------------------------------------+----------------+
   |  Value |                   Name                  |    Reference   |
   +--------+-----------------------------------------+----------------+
   |  TBD1  |     SRv6 unified SIDs is supported is   |     [this      |
   |        |              supported (U)              |   document]    |
   +--------+-----------------------------------------+----------------+

                                  Table 1

7.2.  New LSP Flag Registry

   [RFC8231] defines the LSP object; per that RFC, IANA created a
   registry to manage the value of the LSP object's Flag field.  IANA is
   requested to make allocations from the registry, as follows:

        +---------+----------------------------+------------------+
        |   Value |            Name            |     Reference    |
        +---------+----------------------------+------------------+
        |   TBD2  |  SRv6 Unified SIDs bit (U) | [this document]  |
        |   TBD3  |    UNIFIED-SID-INFO TLV    | [this document]  |
        +---------+----------------------------+------------------+

                                  Table 2

7.3.  Extension for SRv6-ERO Registry

   SRv6-ERO subobject is defined in [I-D.ietf-pce-segment-routing-ipv6],
   and the registry to manage the Flag field of SR-ERO is requested in
   [I-D.ietf-pce-segment-routing-ipv6].  IANA is requested to make
   allocations from the registry, as follows:

    +---------+------------------------------------+------------------+
    |   Value |                Name                |     Reference    |
    +---------+------------------------------------+------------------+
    |   TBD4  |  Extension for SRv6-ERO Subobject  | [this document]  |
    +---------+------------------------------------+------------------+

                                  Table 3



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8.  Normative References

   [I-D.ietf-pce-segment-routing-ipv6]
              Negi, M., Li, C., Sivabalan, S., Kaladharan, P., and Y.
              Zhu, "PCEP Extensions for Segment Routing leveraging the
              IPv6 data plane", draft-ietf-pce-segment-routing-ipv6-04
              (work in progress), March 2020.

   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-15 (work in
              progress), March 2020.

   [I-D.liu-idr-segment-routing-te-policy-complement]
              Yao, L. and S. Peng, "BGP Extensions for Unified SID in TE
              Policy", draft-liu-idr-segment-routing-te-policy-
              complement-02 (work in progress), May 2020.

   [I-D.mirsky-6man-unified-id-sr]
              Cheng, W., Mirsky, G., Peng, S., Aihua, L., Wan, X., and
              C. Wei, "Unified Identifier in IPv6 Segment Routing
              Networks", draft-mirsky-6man-unified-id-sr-06 (work in
              progress), March 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,
              <https://www.rfc-editor.org/info/rfc8231>.







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   [RFC8281]  Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for PCE-Initiated LSP Setup in a Stateful PCE
              Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
              <https://www.rfc-editor.org/info/rfc8281>.

   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.

   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

   [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>.

Authors' Addresses

   Quan Xiong
   ZTE Corporation
   No.6 Huashi Park Rd
   Wuhan, Hubei  430223
   China

   Email: xiong.quan@zte.com.cn


   Shaofu Peng
   ZTE Corporation
   No.50 Software Avenue
   Nanjing, Jiangsu  210012
   China

   Email: peng.shaofu@zte.com.cn










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