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Versions: 00 01

Network Working Group                                         J. He, Ed.
Internet-Draft                                                    B. Nie
Intended status: Standards Track                                 Z. Zhao
Expires: January 1, 2021                                        Ericsson
                                                           June 30, 2020


                           MPLS Entropy Block
                   draft-jiang-mpls-entropy-block-01

Abstract

   Load balancing across MPLS networks requires entropy information to
   be carried in MPLS label stack and to be handled by the downstream
   Label Switching Routers.  This document describes the problems using
   existing approaches and introduces an approach to the solution.

Status of This Memo

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

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   This Internet-Draft will expire on January 1, 2021.

Copyright Notice

   Copyright (c) 2020 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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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Approach  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  End-to-End Processing . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Example 1 Entropy Block advertisement through signaling .   3
     4.2.  Example 2 Entropy Block advertisement through global
           configuration . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Signaling for Entropy Block . . . . . . . . . . . . . . . . .   5
   6.  Issues  . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Anycast Segment . . . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Traffic load balancing improves bandwidth utilization in MPLS
   networks.  The entropy information is required to be carried in MPLS
   label stack of each packet in the MPLS network, and to be handled
   along the path by Label Switching Routers (LSR) towards egress node.
   [RFC6790] provides a technique used in the MPLS data plane to provide
   entropy for load-balancing, using a combination of Entropy Label
   Indicator and Entropy Label.  [RFC6391] provides another technique
   used in the MPLS data plane while only serve for pseudowire based
   services.

   An LSR may have limitations in the number of labels it can push.  It
   may also have a limitation in the number of labels it can inspect
   when looking for entropy information.  The limitations become obvious
   for traffic-engineering applications such as Segment Routing
   [RFC8402] and Resource ReserVation Protocol-Traffic Engineering
   (RSVP-TE) [RFC3209].  Some proposals are discussed in [RFC8662].

   This document describes an approach to mitigate the limitations, by
   allocating a specific MPLS label block for entropy usage.  Thus the
   entropy information can be carried in the MPLS label stack and
   handled by the downstream LSRs.  It adds additional alternatives
   beyond those discussed in [RFC6790] section 2.  This single entropy
   label approach improves efficiency when compared with [RFC6790] which
   uses label pair (ELI/EL).  It also accommodates label location
   flexibility and service agnostic when compared with [RFC6391].
   Considerations from [RFC8662] are still applicable, whether it is
   ELI/EL or EL only.  As described there, systems involved still need



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   to carefully consider issues such as MSD, and determine how many
   entropy labels are needed, and where they need to be placed.  This
   draft reduces the overhead of these labels from 2 labels to 1.

   In the document we see some issues with all the alternatives and are
   looking for further discussion.

2.  Terminology

   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.  Approach

   The entropy information is encoded as an additional label in MPLS
   label stack.  Since the single Entropy Label (EL) is encapsulated by
   an ingress LSR while terminated at an egress LSR, both ingress LSR
   and egress LSR MUST be able to distinguish unambiguously between
   entropy label and other labels.  To accomplish this, a dedicated
   label range is allocated for entropy label, named Entropy Block (EB).

   The Entropy Block can be advertised through signals (E.g. through
   IGP) or globally configured (E.g. through NMS).

   On ingress LSR, when encoding entropy information in MPLS label stack
   towards an egress LSR, the label value shall be in the range of the
   Entropy Block.  When received on the egress LSR and the entropy label
   appears from the MPLS label stack, it is simply popped.

4.  End-to-End Processing

4.1.  Example 1 Entropy Block advertisement through signaling

   In this example, Entropy Block is advertised by each LSR through IGP
   (E.g.  IS-IS).  Each LSR may have different Entropy Block.  One
   traffic flow is forwarded through a Traffic Engineering (TE) tunnel,
   LSR1->LSR4->LSR6.

   On ingress LSR, entropy value is calculated from packet received, and
   adjusted to the Entropy Block of LSR6 as it is to be popped by LSR6.

   On transit LSRs, such as LSR2 or LSR3, the entropy information in the
   packet is utilized for load balancing.  When packet reaches LSR4, the
   steering point of the TE tunnel, the topmost tunnel label is popped




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   and packet continues to egress LSR, LSR6.  After the second tunnel
   label is popped, the entropy label is popped and packet is sent out.


           | ------------------  IGP  ---------------------- |

                                +===== LSR4 ======+
                                |                 |
           LSR1 ==== LSR2 ==== LSR3 ============ LSR5 ==== LSR6

       -->    +---------+               +---------+           -->
       Pkt    | Payload |               | Payload |           Pkt
              +---------+               +---------+
              |   EL6   |               |   EL6   |
              +---------+               +---------+
              |  LSR6   |               |  LSR6   |
              +---------+               +---------+
              |  LSR4   |
              +---------+

            Figure 1: Single EL for TE tunnel LSR1->LSR4->LSR6

4.2.  Example 2 Entropy Block advertisement through global configuration

   In this example, Entropy Block is globally configured by NMS.  All
   LSRs have the identical Entropy Block.  One traffic flow is forwarded
   through a Traffic Engineering (TE) tunnel, LSR1->LSR4->LSR6.  LSR2
   and LSR3 have Less entropy reachability capability.

   Considering the entropy reachability capability on some LSRs, more
   entropy labels are encapsulated in the MPLS stack.  On ingress LSR,
   entropy value is calculated from packet received, and adjusted to
   Entropy Block globally configured.

   On transit LSRs, such as LSR2 or LSR3, the entropy information in the
   packet is utilized for load balancing.  When packet reaches LSR4, the
   steering point of the TE tunnel, the topmost tunnel label is popped
   and the first entropy label is popped.  Then packet continues to
   egress LSR, LSR6.  After the second tunnel label is popped, the
   second entropy label is popped and packet is sent out.











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                  +----------------+
                  |      NMS       |
                  +----------------+
                        / | \

                                +===== LSR4 ======+
                                |                 |
           LSR1 ==== LSR2 ==== LSR3 ============ LSR5 ==== LSR6

       -->    +---------+               +---------+           -->
       Pkt    | Payload |               | Payload |           Pkt
              +---------+               +---------+
              |   ELx   |               |   ELx   |
              +---------+               +---------+
              |  LSR6   |               |  LSR6   |
              +---------+               +---------+
              |   ELx   |
              +---------+
              |  LSR4   |
              +---------+


           Figure 2: Multiple ELs for TE tunnel LSR1->LSR4->LSR6

5.  Signaling for Entropy Block

   The Entropy Block is advertised through signals (E.g.  IGP) with new
   extensions.  It could be represented as range size together with base
   label value, or the two boundary label values.

   The detail formats of the extensions are left for further discussion.

6.  Issues

6.1.  Anycast Segment

   In Segment Routing networks [RFC8402] when anycast segment is
   deployed, special care is required.

   An anycast segment is not reference a particular node, but a group of
   nodes.  In case each node in the group has different Entropy Block,
   ingress LSR cannot encapsulate an appropriate entropy label behind
   the anycast segment in the MPLS stack.

   To ease the use of Entropy Block with anycast segment, it is
   recommended to configure identical Entropy Block on all nodes of a
   particular anycast group.  Using an anycast segment without




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   configuring identical Entropy Block on all nodes belonging to the
   same anycast group may lead to misrouting.

7.  IANA Considerations

   TBD.

8.  Security Considerations

   With the use of the extensions defined in this document, Entropy
   information will be used to program the MPLS data plane [RFC3031].
   Using an anycast segment without configuring identical Entropy Block
   on all nodes belonging to the same anycast group may lead to
   misrouting.

9.  References

9.1.  Normative References

   [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>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [RFC6391]  Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V.,
              Regan, J., and S. Amante, "Flow-Aware Transport of
              Pseudowires over an MPLS Packet Switched Network",
              RFC 6391, DOI 10.17487/RFC6391, November 2011,
              <https://www.rfc-editor.org/info/rfc6391>.

   [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>.








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9.2.  Informative References

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [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

   Jiang He (editor)
   Ericsson
   No. 5, Lize east street, Chaoyang district
   Beijing  100102
   CN

   Email: jiang.he@ericsson.com


   Bolin Nie
   Ericsson
   No. 5, Lize east street, Chaoyang district
   Beijing  100102
   CN

   Email: zephyr.nie@ericsson.com


   Zhenning Zhao
   Ericsson
   No. 5, Lize east street, Chaoyang district
   Beijing  100102
   CN

   Email: navid.zhao@ericsson.com






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