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PCE                                                              S. Peng
Internet-Draft                                                  Q. Xiong
Intended status: Standards Track                         ZTE Corporation
Expires: March 14, 2020                               September 11, 2019


           PCEP Extension for SR-MPLS Entropy Label Position
                draft-peng-pce-entropy-label-position-01

Abstract

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

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
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   This Internet-Draft will expire on March 14, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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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 . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  The OPEN Object . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  The LSP Object  . . . . . . . . . . . . . . . . . . . . .   4
       3.2.1.  The LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . .   5
     3.3.  The ERO Object  . . . . . . . . . . . . . . . . . . . . .   5
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  New SR PCE Capability Flag Registry . . . . . . . . . . .   6
     7.2.  New LSP Flag Registry . . . . . . . . . . . . . . . . . .   6
     7.3.  New SR-ERO Flag Registry  . . . . . . . . . . . . . . . .   7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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 [I-D.ietf-spring-segment-routing-mpls].  SR-MPLS leverages
   the MPLS label stack to construct the SR path.  PCEP Extensions for
   Segment Routing [I-D.ietf-pce-segment-routing] 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 provide entropy for 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



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   based on several fields from a given packet and places the result in
   an 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.

   [I-D.ietf-mpls-spring-entropy-label] 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
   would consider the following goals:

   o  a limited number of <ELI, EL> pairs should be inserted deeper in
      the label-stack.

   o  the inserted position should be whithin the ERLD of most transit
      nodes.

   o  a minimum number of <ELI, EL> to satisfy the above criteria.

   In some cases, It is required for the controller (e.g.  PCE) to
   perform the TE path computation as well as the Entropy Label Position
   (ELP), because the contoller has the ERLD information of all nodes,
   especially 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],
   [I-D.ietf-pce-segment-routing] and
   [I-D.ietf-mpls-spring-entropy-label].

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.





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3.  PCEP Extensions

3.1.  The OPEN Object

   As defined in [I-D.ietf-pce-segment-routing], 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 1.


           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 1: E-flag in SR-PCE-CAPABILITY sub-TLV

   E (ELP Configuration is supported) : A PCC or PCE sets this flag bit
   to 1 carried in Open message to indicate that it supports the SR path
   with ELP configuration.

3.2.  The LSP Object

   The LSP Object is defined in Section 7.3 of [RFC8231].  This document
   defiend a new flag (E-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|E|C|  O  |A|R|S|D|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                        TLVs                                 //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                      Figure 2: E-flag in LSP Object

   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




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   ELP information is included by PCE and encoded in the PCRep, PCUpd or
   PCInitiate message.

3.2.1.  The LSP-EXTENDED-FLAG TLV

   As defined in [RFC8231], the length of LSP Object Flag field is 12
   bits and it defined the value from bit 5 to bit 11.  The bits from 1
   to 3 are defined in [RFC8623], the bit value 4 is used in [RFC8281].
   So all bits of the flag has been used and this document proposes to
   define a new LSP-EXTENDED-FLAG TLV for LSP object to extend the
   length of the flag as the Figure 3 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Type=TBD             |       Length                 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Extended Flag                         |E|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                  Figure 3: LSP-EXTENDED-FLAG TLV Format

   The bit E has the same defination with section 3.2 and the other bits
   of the Extended flag can be used for other drafts in the future.

3.3.  The ERO Object

   SR-ERO subobject is used for SR-TE path which consists of one or more
   SIDs as defined in [I-D.ietf-pce-segment-routing].  This document
   defiend a new flag (E-flag) for the SR-ERO subobject as Figure 3
   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




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   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.

4.  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>.

5.  Security Considerations

   TBA

6.  Acknowledgements

   TBA

7.  IANA Considerations

7.1.  New SR PCE Capability Flag Registry

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

    +--------+-------------------------------------+------------------+
    | Value  |                 Name                |    Reference     |
    +--------+-------------------------------------+------------------+
    | TBD11  |  ELP Configuration is supported (E) | [this 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:





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

                                  Table 2

7.3.  New SR-ERO Flag Registry

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

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

                                  Table 3

8.  Normative References

   [I-D.ietf-mpls-spring-entropy-label]
              Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
              Shakir, R., and J. Tantsura, "Entropy label for SPRING
              tunnels", draft-ietf-mpls-spring-entropy-label-12 (work in
              progress), July 2018.

   [I-D.ietf-pce-segment-routing]
              Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "PCEP Extensions for Segment Routing",
              draft-ietf-pce-segment-routing-16 (work in progress),
              March 2019.

   [I-D.ietf-spring-segment-routing-mpls]
              Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing with MPLS
              data plane", draft-ietf-spring-segment-routing-mpls-22
              (work in progress), May 2019.

   [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>.



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   [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>.

Authors' Addresses

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

   Email: peng.shaofu@zte.com.cn










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

   Email: xiong.quan@zte.com.cn












































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