PCEP Extension for SR-MPLS Entropy Label Position
draft-peng-pce-entropy-label-position-05

PCE                                                              S. Peng
Internet-Draft                                                  Q. Xiong
Intended status: Standards Track                         ZTE Corporation
Expires: August 23, 2021                                          F. Qin
                                                            China Mobile
                                                       February 19, 2021

           PCEP Extension for SR-MPLS Entropy Label Position
                draft-peng-pce-entropy-label-position-05

Abstract

   This document proposes a set of extensions for PCEP to configure the
   entropy label position for SR-MPLS networks.

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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.  Entropy Labels in SR-MPLS Scenario with PCE . . . . . . . . .   3
   4.  PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  The OPEN Object . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  The LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . . . .   5
     4.3.  The ERO Object  . . . . . . . . . . . . . . . . . . . . .   6
   5.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  New SR PCE Capability Flag Registry . . . . . . . . . . .   7
     8.2.  New LSP-EXTENDED-FLAG Flag Registry . . . . . . . . . . .   7
     8.3.  New SR-ERO Flag Registry  . . . . . . . . . . . . . . . .   7
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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, as well as a PCC to request a path subject to
   certain constraint(s) and optimization criteria in SR networks.

   Entropy label (EL) [RFC6790] is a technique used in the MPLS data
   plane to improve load-balancing.  Entropy Label Indicator (ELI) can
   be immediately preceding an EL in the MPLS label stack.  The idea
   behind the EL is that the ingress router computes a hash based on
   several fields from a given packet and places the result in an

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   additional label, named "entropy label".  Then, this entropy label
   can be used as part of the hash keys used by an LSR.  Using the
   entropy label as part of the hash keys reduces the need for deep
   packet inspection in the LSR while keeping a good level of entropy in
   the load-balancing.  When the entropy label is used, the keys used in
   the hashing functions are still a local configuration matter and an
   LSR may use solely the entropy label or a combination of multiple
   fields from the incoming packet.

   [RFC8662] proposes to use entropy labels for SR-MPLS networks and
   mutiple <ELI, EL> pairs SHOULD be inserted in the SR-MPLS label
   stack.  The ingress node may decide the number and place of the ELI/
   ELs which need to be inserted into the label stack.  But in some
   cases, the the controller (e.g.  PCE) could be used to perform the TE
   path computation as well as the Entropy Label Position (ELP) which is
   useful for inter-domain scenarios.  This document proposes a set of
   extensions for PCEP to configure the ELP information for SR-MPLS
   networks.

2.  Conventions used in this document

2.1.  Terminology

   The terminology is defined as [RFC5440], [RFC6790], [RFC8664] and
   [RFC8662].

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.  Entropy Labels in SR-MPLS Scenario with PCE

   [RFC8662] proposes to use entropy labels for SR-MPLS networks.  The
   Entropy Readable Label Depth (ERLD) is defined as the number of
   labels which means that the router will perform load-balancing using
   the ELI/EL.  An appropriate algorithm should consider the following
   criteria:

   o  a limited number of <ELI, EL> pairs SHOULD be inserted in the SR-
      MPLS label stack;

   o  the inserted positions SHOULD be whithin the ERLD of a maximize
      number of transit LSRs;

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   o  a minimum number of <ELI, EL> pairs SHOULD be inserted while
      satisfying the above criteria.

   As the Figure 1 shown, in SR-MPLS inter-domain scenario, the ingress
   node of the first domain could not get the ERLD information of other
   nodes of other domains.  The PCE MAY perform the computation of the
   end-to-end path as well as the the Entropy Label Position (ELP)
   including the number and the place of the ELI/ELs.  The ingress nodes
   MUST support the capabilities of inserting multiple ELI/ELs and
   advertise the capabilities to the PCEs.  The PCEs SHOULD get the
   information of all nodes such as MSD, ELC and ERLD through IGP/BGP-LS
   protocol.

          +-----+                +-----+                 +-----+
          |PCE-1|                |PCE-2|                 |PCE-3|
          +--+--+                +--+--+                 +--+--+
             |                      |                       |
    .........+..........   .........+..........    .........+...........
    .                  .   .                  .    .                   .
    .+---+       +---+ .   . +---+      +---+ .    .+---+      +----+  .
    .| A |-------| B |------ | C |------| X |-------| Y |------| Z  |  .
    .+---+       +---+ .   . +---+      +---+ .    .+---+      +----+  .
    .    SR-AS 1       .   .   SR-AS 2        .    .     SR-AS 3       .
    ....................   ....................    .....................

         Figure 1: Entropy Labels in SR-MPLS Inter-Domain Scenario

4.  PCEP Extensions

4.1.  The OPEN Object

   As defined in [RFC8664], PCEP speakers use SR PCE Capability sub-TLV
   to exchange information about their SR capability when PST=1 in the
   PST List of the PATH-SETUP-TYPE-CAPABILITY TLV carried in Open
   object.  This document defined a new flag (E-flag) for SR PCE
   Capability sub-TLV as shown in Figure 2.

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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=TBD11            |            Length=4           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Reserved              |   Flags |E|N|X|      MSD      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 2: E-flag in SR-PCE-CAPABILITY sub-TLV

   E (Entropy Label Configuration is supported) : A PCE sets this flag
   bit to 1 carried in Open message to indicate that it supports the
   computation of SR path with ELP information.  A PCC sets this flag to
   1 to indicate that it supports the capability of inserting multiple
   ELI/EL pairs and and supports the results of SR path with ELP from
   PCE.

4.2.  The LSP-EXTENDED-FLAG TLV

   The LSP Object is defined in Section 7.3 of [RFC8231].  This document
   defiend a new flag (E-flag) for the LSP-EXTENDED-FLAG TLV carried in
   LSP Object as defined in [I-D.xiong-pce-lsp-flag].  The format is
   shown as Figure 3:

       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=TBD            |          Length               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                             |E|
       //                 LSP Extended Flags                          //
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 3: E-flag in LSP-EXTENDED-FLAG TLV

   E (Request for ELP Configuration) : If the bit is set to 1, it
   indicates that the PCC requests PCE to compute the SR path with ELP
   information.  A PCE would also set this bit to 1 to indicate that the
   ELP information is included by PCE and encoded in the PCRep, PCUpd or
   PCInitiate message.

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4.3.  The ERO Object

   SR-ERO subobject is used for SR-TE path which consists of one or more
   SIDs as defined in [RFC8664].  This document defiend a new flag
   (E-flag) for the SR-ERO subobject as Figure 4 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=36   |     Length    |  NT   |     Flags   |E|F|S|C|M|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         SID (optional)                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //                   NAI (variable, optional)                  //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 4: E-flag in SR-ERO subobject

   E (ELP Configuration) : If this flag is set, it means that the
   position after this SR-ERO subobject is the position to insert <ELI,
   EL>, otherwise it cannot insert <ELI, EL> after this segment.

5.  Operations

   The SR path is initiated by PCE or PCC with PCReq, PCInitiated or
   PCUpd messages and the E bit is set to 1 in LSP object to request the
   ELP configuration.  The SR-TE path being recieved by PCC with SR-ERO
   segment list, for example, <S1, S2, S3, S4, S5, S6>, especially S3
   and S6 with E-flag set.  It indicates that two <ELI, EL> pairs MUST
   be inserted into the label stack of the SR-TE forwarding entry,
   repectively after the label for S3 and label for S6.  With EL
   information, the label stack for SR-MPLS would be <label1, label2,
   label3, ELI, EL, label4, label5, label6, ELI, EL>.

6.  Security Considerations

   TBA

7.  Acknowledgements

   TBA

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8.  IANA Considerations

8.1.  New SR PCE Capability Flag Registry

   SR PCE Capability TLV is defined in [RFC8664], and the registry to
   manage the Flag field of the SR PCE Capability TLV is requested in
   [RFC8664].  IANA is requested to make allocations from the registry,
   as follows:

   +--------+-----------------------------------------+----------------+
   |  Value |                   Name                  |    Reference   |
   +--------+-----------------------------------------+----------------+
   |  TBD11 |      Entropy Label Configuration is     |     [this      |
   |        |              supported (E)              |   document]    |
   +--------+-----------------------------------------+----------------+

                                  Table 1

8.2.  New LSP-EXTENDED-FLAG Flag Registry

   [I-D.xiong-pce-lsp-flag] defines the LSP-EXTENDED-FLAG TLV.  IANA is
   requested to make allocations from the Flag field registry, as
   follows:

   +---------+-------------------------------------+------------------+
   |   Value |                 Name                |     Reference    |
   +---------+-------------------------------------+------------------+
   |    TBD  |   Request for ELP Configuration (E) | [this document]  |
   +---------+-------------------------------------+------------------+

                                  Table 2

8.3.  New SR-ERO Flag Registry

   SR-ERO subobject is defined in [RFC8664], and the registry to manage
   the Flag field of SR-ERO is requested in [RFC8664].  IANA is
   requested to make allocations from the registry, as follows:

         +---------+-------------------------+------------------+
         |   Value |           Name          |     Reference    |
         +---------+-------------------------+------------------+
         |    36   |   ELP Configuration (E) | [this document]  |
         +---------+-------------------------+------------------+

                                  Table 3

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9.  Normative References

   [I-D.xiong-pce-lsp-flag]
              Xiong, Q., "LSP Object Flag Extension of Stateful PCE",
              draft-xiong-pce-lsp-flag-02 (work in progress), May 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>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [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>.

   [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>.

   [RFC8623]  Palle, U., Dhody, D., Tanaka, Y., and V. Beeram, "Stateful
              Path Computation Element (PCE) Protocol Extensions for
              Usage with Point-to-Multipoint TE Label Switched Paths
              (LSPs)", RFC 8623, DOI 10.17487/RFC8623, June 2019,
              <https://www.rfc-editor.org/info/rfc8623>.

   [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>.

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   [RFC8662]  Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
              Shakir, R., and J. Tantsura, "Entropy Label for Source
              Packet Routing in Networking (SPRING) Tunnels", RFC 8662,
              DOI 10.17487/RFC8662, December 2019,
              <https://www.rfc-editor.org/info/rfc8662>.

   [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>.

Authors' Addresses

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

   Email: peng.shaofu@zte.com.cn

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

   Email: xiong.quan@zte.com.cn

   Fengwei Qin
   China Mobile
   Beijing
   China

   Email: qinfengwei@chinamobile.com

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