Path Computation Element Communication Protocol (PCEP) Extension for SR-MPLS Entropy Label Positions
draft-peng-pce-entropy-label-position-10

PCE                                                             Q. Xiong
Internet-Draft                                                   S. Peng
Intended status: Standards Track                         ZTE Corporation
Expires: 12 April 2024                                            F. Qin
                                                            China Mobile
                                                                 J. Zhao
                                                                   CAICT
                                                         10 October 2023

Path Computation Element Communication Protocol (PCEP) Extension for SR-
                      MPLS Entropy Label Positions
                draft-peng-pce-entropy-label-position-10

Abstract

   Entropy label (EL) can be used in the SR-MPLS data plane to improve
   load-balancing and multiple Entropy Label Indicator (ELI)/EL pairs
   SHOULD be inserted in the SR-MPLS label stack.

   This document proposes a set of extensions for Path Computation
   Element Communication Protocol (PCEP) to configure the entropy label
   positions 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-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 12 April 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Xiong, et al.             Expires 12 April 2024                 [Page 1]
Internet-Draft      PCEP for Entropy Label Positions        October 2023

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  Entropy Labels in SR-MPLS Scenario with PCE . . . . . . . . .   4
   4.  PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  The OPEN Object . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  The LSP-EXTENDED-FLAG TLV . . . . . . . . . . . . . . . .   5
     4.3.  The SR-ERO Object . . . . . . . . . . . . . . . . . . . .   6
   5.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  New SR PCE Capability Flag Registry . . . . . . . . . . .   6
     7.2.  New LSP-EXTENDED-FLAG Flag Registry . . . . . . . . . . .   7
     7.3.  New SR-ERO Flag Registry  . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   [RFC5440] describes the Path Computation Element Computation 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.

Xiong, et al.             Expires 12 April 2024                 [Page 2]
Internet-Draft      PCEP for Entropy Label Positions        October 2023

   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
   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
   multiple <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.  The extensions
   for Border Gateway Protocol (BGP) to indicate the entropy label
   positions in the SR-MPLS label stack has been proposed in
   [I-D.ietf-idr-bgp-srmpls-elp].

   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].

Xiong, et al.             Expires 12 April 2024                 [Page 3]
Internet-Draft      PCEP for Entropy Label Positions        October 2023

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.

   As described in [RFC8662] section 7, the ERLD value is important for
   inserting ELI/EL and the ingress node need to evaluate the minimum
   ERLD value along the node segment path.  But it will add complexity
   in the ELI/EL insertion process.  Moreover, the ingress node cannot
   find the minimum ERLD along the path and does not support the
   computation of the minimum ERLD especially in inter-domain scenarios.
   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.

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

Xiong, et al.             Expires 12 April 2024                 [Page 4]
Internet-Draft      PCEP for Entropy Label Positions        October 2023

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

   The PCEs could get the information of all nodes such as Maximum SID
   Depth (MSD) (e.g.  Base MPLS Imposition MSD (BMI-MSD) or ERLD-MSD)
   through Interior Gateway Protocol (IGP) and can compute the minimum
   ERLD along the end-to-end path.  IS-IS [RFC8491] and OSPF [RFC8476]
   provide examples of advertisement of the MSD.  The ERLD value can be
   collected via IS-IS [RFC9088], and OSPF [RFC9089].  Moreover, the
   PCEs also can compute the Entropy Label Position (ELP) including the
   number and the places of the ELI/ELs.  Then the ingress nodes MAY be
   required to support the capabilities of inserting multiple ELI/ELs
   and need to advertise the capabilities to the PCEs.

   This document proposes the extensions for PCE to perform the
   computation of the end-to-end path as well as the positions of
   entropy labels in SR-MPLS networks.  The ingress nodes can directly
   insert the ELI/ELs based on the positions.

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.

   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
   defined a new flag (E-flag) for the LSP-EXTENDED-FLAG TLV carried in
   LSP Object as defined in [RFC9357].

   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.

Xiong, et al.             Expires 12 April 2024                 [Page 5]
Internet-Draft      PCEP for Entropy Label Positions        October 2023

4.3.  The SR-ERO Object

   SR-ERO subobject is used for SR-TE path which consists of one or more
   SIDs as defined in [RFC8664].  This document defined a new flag
   (E-flag) for the 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 received 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,
   respectively 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

   This document defines a new E bit for entropy label, which do not
   introduce any new security considerations beyond those already listed
   in [RFC9357], [RFC8662] and [RFC8664].

   Note that this specification enables a network controller to insert
   ELI/ELs pairs and an attacker may set the E bit in SR-ERO subobject
   incorrectly and exceed the length of stack.

7.  IANA Considerations

7.1.  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:

Xiong, et al.             Expires 12 April 2024                 [Page 6]
Internet-Draft      PCEP for Entropy Label Positions        October 2023

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

                                 Table 1

7.2.  New LSP-EXTENDED-FLAG Flag Registry

   [RFC9357] 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

7.3.  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

8.  Acknowledgements

   The authors would like to thank Stephane Litkowski, Dhruv Dhody,
   Tarek Saad, Zhenbin Li and Jeff Tantsura for their review,
   suggestions and comments to this document.

9.  References

9.1.  Normative References

Xiong, et al.             Expires 12 April 2024                 [Page 7]
Internet-Draft      PCEP for Entropy Label Positions        October 2023

   [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>.

   [RFC8476]  Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
              "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
              DOI 10.17487/RFC8476, December 2018,
              <https://www.rfc-editor.org/info/rfc8476>.

   [RFC8491]  Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
              DOI 10.17487/RFC8491, November 2018,
              <https://www.rfc-editor.org/info/rfc8491>.

   [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>.

Xiong, et al.             Expires 12 April 2024                 [Page 8]
Internet-Draft      PCEP for Entropy Label Positions        October 2023

   [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>.

   [RFC9088]  Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
              and M. Bocci, "Signaling Entropy Label Capability and
              Entropy Readable Label Depth Using IS-IS", RFC 9088,
              DOI 10.17487/RFC9088, August 2021,
              <https://www.rfc-editor.org/info/rfc9088>.

   [RFC9089]  Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
              and M. Bocci, "Signaling Entropy Label Capability and
              Entropy Readable Label Depth Using OSPF", RFC 9089,
              DOI 10.17487/RFC9089, August 2021,
              <https://www.rfc-editor.org/info/rfc9089>.

   [RFC9357]  Xiong, Q., "Label Switched Path (LSP) Object Flag
              Extension for Stateful PCE", RFC 9357,
              DOI 10.17487/RFC9357, February 2023,
              <https://www.rfc-editor.org/info/rfc9357>.

9.2.  Informative References

   [I-D.ietf-idr-bgp-srmpls-elp]
              Liu, Y. and S. Peng, "BGP Extension for SR-MPLS Entropy
              Label Position", Work in Progress, Internet-Draft, draft-
              ietf-idr-bgp-srmpls-elp-00, 1 August 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
              srmpls-elp-00>.

Authors' Addresses

   Quan Xiong
   ZTE Corporation
   No.6 Huashi Park Rd
   Wuhan
   Hubei, 430223
   China
   Email: xiong.quan@zte.com.cn

Xiong, et al.             Expires 12 April 2024                 [Page 9]
Internet-Draft      PCEP for Entropy Label Positions        October 2023

   Shaofu Peng
   ZTE Corporation
   No.50 Software Avenue
   Nanjing
   Jiangsu, 210012
   China
   Email: peng.shaofu@zte.com.cn

   Fengwei Qin
   China Mobile
   Beijing
   China
   Email: qinfengwei@chinamobile.com

   Junfeng Zhao
   CAICT
   Beijing
   China
   Email: zhaojunfeng@caict.ac.cn

Xiong, et al.             Expires 12 April 2024                [Page 10]