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Versions: 00 01 02 03                                                   
IDR Working Group                                               Yao. Liu
Internet-Draft                                              Shaofu. Peng
Intended status: Standards Track                               ZTE Corp.
Expires: August 26, 2021                               February 22, 2021


            BGP Extension for SR-MPLS Entropy Label Position
                    draft-zhou-idr-bgp-srmpls-elp-02

Abstract

   This document proposes extensions for BGP to indicate the entropy
   label position in the SR-MPLS label stack when distributing SR Policy
   candidate paths.

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
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   This Internet-Draft will expire on August 26, 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  Terminology and Acronyms  . . . . . . . . . . . . . . . .   3
   3.  Entropy Labels in SR-MPLS Scenario with a Controller  . . . .   3
   4.  BGP Extensions  . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   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.

   Entropy labels (ELs) [RFC6790] are used in the MPLS data plane to
   provide entropy for load-balancing.  The idea behind the entropy
   label 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.

   [RFC8662] proposes to use entropy labels for SR-MPLS networks and
   mutiple < ELI, EL> pairs may be inserted in the SR-MPLS label stack.
   The ingress node may decide the number and position of the ELI/ELs
   which need to be inserted into the label stack, that is termed as ELP
   (Entropy Label Position).  In some cases, centralized controllers are
   used to perform the TE path computation for intra or inter-domain
   scenarios, thus it is also the responsibility of the controller to
   calculate ELP and inform it to the headend of the SR-TE path.

   [I-D.ietf-idr-segment-routing-te-policy] defines the specific process
   of how the controller/PCE in the SR network passes the path
   calculation result of the SR-TE policy to the headend of the network
   through BGP.






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   This document proposes extensions for BGP to indicate the ELP in the
   segment list when distribute SR Policy candidate paths using BGP for
   SR-MPLS networks.

2.  Conventions used in this document

2.1.  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.

2.2.  Terminology and Acronyms

   EL: Entropy Label

   ELI: Entropy Label Indicator

   ELC: Entropy Label Capability

   ERLD: Entropy Readable Label Depth

   ELP: Entropy Label Position

   MSD: Maximum SID Depth

3.  Entropy Labels in SR-MPLS Scenario with a Controller

   [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;

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

   As shown in Figure 1, in SR-MPLS inter-domain scenario, an path from
   A to Z is required, a centralized controller performs the computation
   of the end-to-end path, along which traffic load-balancing is



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   required.  The controller can also be used to perform the computation
   of the the Entropy Label Position (ELP) of the segment list that
   corresponds to the path.  The ELP includs the number and the position
   of the ELI/ELs.

   Multiple limitations MUST be taken into account by the controller
   during path calculation, including Entropy Readable Label Depth
   (ERLD) and Maximum SID Depth (MSD) etc.  The ERLD is defined as the
   number of labels which means that the node will perform load-
   balancing using the ELI/EL pairs.  And each ELI/EL pair must be
   within the ERLD of the node.  The Maximum SID Depth (MSD) defines the
   maximum number of any kind of labels(service, entropy, transport,
   etc.) and it is a limit when the ingress node imposing ELI/EL pairs
   on the SR label stack.

   The controller can get ERLD value and MSD via protocols.  The ERLD
   value can be advertised via IS-IS[I-D.ietf-isis-mpls-elc],
   OSPF[I-D.ietf-ospf-mpls-elc], BGP-
   LS[I-D.ietf-idr-bgp-ls-segment-routing-ext].  [RFC8476], [RFC8491],
   and[RFC8814] provide examples of advertisement of the MSD.

   As specified in section 7.2 [RFC8662], other criteria includes
   segment type, preference for a part of the path, and etc.  It's a
   matter of implementation.

    ....................   ....................    .....................
    .                  .   .                  .    .                   .
    .+---+       +---+ .   . +---+      +---+ .    .+---+      +----+  .
    .| A |-------| B |------ | C |------| X |-------| Y |------| Z  |  .
    .+---+       +---+ .   . +---+      +---+ .    .+---+      +----+  .
    .     domain 1     .   .      domain 2    .    .     domain 3      .
    ....................   ....................    .....................

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

4.  BGP Extensions

   The Segment Flags for Segment Sub-TLVs are defined in
   Section 2.4.4.2.12 of [I-D.ietf-idr-segment-routing-te-policy].  In
   this document, the ELP information is transmitted by extending the
   flags of Segment Sub-TLVs.

       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      |V|A|S|B|E|     |
      +-+-+-+-+-+-+-+-+





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   E-Flag: This flag, when set, indicates that presence of < ELI, EL>
   label pairs which are inserted after this segment.  E-Flag is
   applicable to Segment Types A, C, D, E, F, G and H.  If E-Flag
   appears with Segment Types B, I, J and K, it MUST be ignored. .

5.  Operations

   Node A receives an SR Policy NLRI with an Segment List sub-TLV from
   the controller.  The Segment List sub-TLV contains multiple Segment
   sub-TLVs, for example, <S1, S2, S3, S4, S5, S6>, the E-Flags of S3
   and S6 are set, it indicates that if load-balancing is required, two
   <ELI, EL> pairs SHOULD be inserted into the label stack of the SR-TE
   forwarding entry, respectively after the Label for S3 and Label for
   S6.

   The value of EL is supplemented by the ingress node according to
   load-balancing function of the appropriate keys extracted from a
   given packet.  After inserting ELI/ELs, the label stack on the
   ingress node would be <label1, label2, label3, ELI, EL, label4,
   label5, label6, ELI, EL>.

6.  Security Considerations

   TBD

7.  IANA Considerations

   This document requests bit 4 for Entropy Label Flag.

       Bit     Description                                Reference
      ------------------------------------------------------------------
        4     Entropy Label Position Flag(E-Flag)         This document

8.  References

8.1.  Normative References

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
              Rosen, E., Jain, D., and S. Lin, "Advertising Segment
              Routing Policies in BGP", draft-ietf-idr-segment-routing-
              te-policy-11 (work in progress), November 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>.




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   [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>.

   [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>.

8.2.  Informative References

   [I-D.ietf-idr-bgp-ls-segment-routing-ext]
              Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
              and M. Chen, "BGP Link-State extensions for Segment
              Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
              (work in progress), June 2019.

   [I-D.ietf-isis-mpls-elc]
              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", draft-ietf-
              isis-mpls-elc-13 (work in progress), May 2020.

   [I-D.ietf-ospf-mpls-elc]
              Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
              and M. Bocci, "Signaling Entropy Label Capability and
              Entropy Readable Label Depth Using OSPF", draft-ietf-ospf-
              mpls-elc-15 (work in progress), June 2020.

   [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>.







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   [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>.

   [RFC8814]  Tantsura, J., Chunduri, U., Talaulikar, K., Mirsky, G.,
              and N. Triantafillis, "Signaling Maximum SID Depth (MSD)
              Using the Border Gateway Protocol - Link State", RFC 8814,
              DOI 10.17487/RFC8814, August 2020,
              <https://www.rfc-editor.org/info/rfc8814>.

Authors' Addresses

   Liu Yao
   ZTE Corp.

   Email: liu.yao71@zte.com.cn


   Peng Shaofu
   ZTE Corp.

   Email: peng.shaofu@zte.com.cn



























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