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IDR Working Group                                               Yao. Liu
Internet-Draft                                              Shaofu. Peng
Intended status: Standards Track                               ZTE Corp.
Expires: February 22, 2021                               August 21, 2020


            BGP Extension for SR-MPLS Entropy Label Position
                    draft-zhou-idr-bgp-srmpls-elp-01

Abstract

   This document proposed an extension for BGP to configure the entropy
   label position for SR-MPLS networks.

Status of This Memo

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   This Internet-Draft will expire on February 22, 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Entropy Labels in SR-MPLS Scenario with a Controller  . . . .   2
   3.  BGP Extensions  . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   Entropy Label(EL) [RFC6790]is a technology that can be used for load-
   balancing in Segment Routing (SR) MPLS.

   [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 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, the
   controller is 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 in the SR network passes the path calculation
   result of the SR-TE policy to the headend of the network through BGP.

   In this document, the ELP information is transmitted by extending the
   flags of Segment List Sub-TLV in the BGP.

2.  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.



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   As shown in Figure 1 , in SR-MPLS inter-domain scenario, the
   controller may perform the computation of the end-to-end path as well
   as the the Entropy Label Position (ELP) including the number and the
   position of the ELI/ELs.  The controller has the capability to get
   the ERLD information of all nodes in inter-domain scenarios.

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

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

3.  BGP Extensions

   The Segment Flags is defined in Section 2.4.3.2.12 of
   [I-D.ietf-idr-segment-routing-te-policy].

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

   E-Flag: This flag indicates that presence of < ELI, EL> label pairs
   are inserted after this segment.  It is applicable to all SR-MPLS
   Segment Types.

4.  Operations

   Supposed the head end had received a SR-TE path from the controller
   with multiple Segment List Sub-TLVs, for example, <S1, S2, S3, S4,
   S5, S6>, especially S3 and S6 with E-flag.  It indicates that 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.  With EL information, the label stack for SR-MPLS would be
   <label1, label2, label3, ELI, EL, label4, label5, label6, ELI, EL>.

   Note that the value of EL is supplemented by headend, according to
   load-balancing function of the appropriate keys extracted from a
   given packet.








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5.  IANA Considerations

   This document requests bit 2 for Entropy Label Flag.

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

6.  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-09 (work in progress), May 2020.

   [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>.

   [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>.

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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