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OSPF Working Group                                                 X. Xu
Internet-Draft                                               Alibaba Inc
Intended status: Standards Track                                 S. Kini
Expires: April 27, 2020
                                                               P. Psenak
                                                             C. Filsfils
                                                            S. Litkowski
                                                     Cisco Systems, Inc.
                                                                M. Bocci
                                                                   Nokia
                                                        October 25, 2019


  Signaling Entropy Label Capability and Entropy Readable Label-stack
                            Depth Using OSPF
                      draft-ietf-ospf-mpls-elc-12

Abstract

   Multiprotocol Label Switching (MPLS) has defined a mechanism to load-
   balance traffic flows using Entropy Labels (EL).  An ingress Label
   Switching Router (LSR) cannot insert ELs for packets going into a
   given tunnel unless an egress LSR has indicated via signaling that it
   has the capability to process ELs, referred to as Entropy Label
   Capability (ELC), on that tunnel.  In addition, it would be useful
   for ingress LSRs to know each LSR's capability of reading the maximum
   label stack depth and performing EL-based load-balancing, referred to
   as Entropy Readable Label Depth (ERLD).  This document defines a
   mechanism to signal these two capabilities using OSPF and OSPFv3.
   These mechanism is particularly useful in the environment where
   Segment Routing (SR) is used, where label advertisements are done via
   protocols like OSPF and OSPFv3.

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
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   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."




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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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Advertising ELC Using OSPF  . . . . . . . . . . . . . . . . .   3
     3.1.  Advertising ELC Using OSPFv2  . . . . . . . . . . . . . .   4
     3.2.  Advertising ELC Using OSPFv3  . . . . . . . . . . . . . .   4
   4.  Advertising ERLD Using OSPF . . . . . . . . . . . . . . . . .   4
   5.  Signaling ELC and ERLD in BGP-LS  . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   5
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   [RFC6790] describes a method to load-balance Multiprotocol Label
   Switching (MPLS) traffic flows using Entropy Labels (EL).  It also
   introduces the concept of Entropy Label Capability (ELC) and defines
   the signaling of this capability via MPLS signaling protocols.
   Recently, mechanisms have been defined to signal labels via link-
   state Interior Gateway Protocols (IGP) such as OSPF
   [I-D.ietf-ospf-segment-routing-extensions].  In such scenarios, the
   signaling mechanisms defined in [RFC6790] are inadequate.  This draft
   defines a mechanism to signal the ELC using OSPF.  This mechanism is
   useful when the label advertisement is also done via OSPF.




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   In addition, in the cases where stacked LSPs are used for whatever
   reasons (e.g., SR-MPLS [I-D.ietf-spring-segment-routing-mpls]), it
   would be useful for ingress LSRs to know each intermediate LSR's
   capability of reading the maximum label stack depth and performing
   EL-based load-balancing.  This capability, referred to as Entropy
   Readable Label Depth (ERLD) as defined in
   [I-D.ietf-mpls-spring-entropy-label] may be used by ingress LSRs to
   determine the position of the EL label in the stack, and whether it's
   necessary to insert multiple ELs at different positions in the label
   stack.

2.  Terminology

   This document makes use of the terms defined in [RFC6790], [RFC7770]
   and [I-D.ietf-mpls-spring-entropy-label].

   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
   [BCP14] [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Advertising ELC Using OSPF

   Even though ELC is a property of the node, in some cases it is
   advantageous to associate and advertise the ELC with the prefix.  In
   multi-area networks, routers may not know the identity of the prefix
   originator in a remote area, or may not know the capabilities of such
   originator.  Similarly, in a multi domain network, the identity of
   the prefix originator and its capabilities may not be known to the
   ingress LSR.

   If a router has multiple line cards, the router MUST NOT announce ELC
   unless all of its line-cards are capable of processing ELs.

   If the router supports ELs on all of its line cards, it SHOULD
   advertise the ELC with every local host prefix it advertises in OSPF.

   When an OSPF Area Border Router (ABR) advertises the prefix to the
   connected area based on the intra-area or inter-area prefix that is
   reachable in some other area, it MUST preserve the ELC signalling for
   such prefix.

   When an OSPF Autonomous System Boundary Router (ASBR) redistributes
   the prefix from another instance of the OSPF or from some other
   protocol, it SHOULD preserve the ELC signaling for the prefix.  The
   exact mechanism used to exchange ELC between protocol instances on




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   the ASBR is outside of the scope of this document and is
   implementation specific.

3.1.  Advertising ELC Using OSPFv2

   [RFC7684] defines the OSPFv2 Extended Prefix TLV to advertise
   additional attributes associated with a prefix.  The OSPFv2 Extended
   Prefix TLV includes a one octet Flags field.  A new flag in the Flags
   field is used to signal the ELC for the prefix:

      0x20 - E-Flag (ELC Flag): Set by the advertising router to
      indicate that the prefix originator is capable of processing ELs.

3.2.  Advertising ELC Using OSPFv3

   [RFC5340] defines the OSPFv3 PrefixOptions that are advertised along
   with the prefix.  A new bit in the OSPFV3 PrefixOptions is used to
   signal the ELC for the prefix:

      0x04 - E-Flag (ELC Flag): Set by the advertising router to
      indicate that the prefix originator is capable of processing ELs.

4.  Advertising ERLD Using OSPF

   A new MSD (Maximum SID Depth) type of the Node MSD sub-TLV [RFC8476],
   called ERLD is defined to advertise the ERLD of a given router.  The
   scope of the advertisement depends on the application.

   Assignment of a MSD-Type for ERLD is defined in
   [I-D.ietf-isis-mpls-elc].

   If a router has multiple line-cards with different capabilities for
   reading the maximum label stack depth, the router MUST advertise the
   smallest one.

   When the ERLD MSD-Type is received in the OSPFv2 or OSPFv3 Link MSD
   Sub-TLV, it MUST be ignored.

5.  Signaling ELC and ERLD in BGP-LS

   The OSPF extensions defined in this document can be advertised via
   BGP-LS [RFC7752] using existing BGP-LS TLVs.

   The ELC Flag included in the OSPFv2 Extended Prefix TLV and the
   OSPFv3 PrefixOptions, as defined in Section 3, is advertised using
   the Prefix Attribute Flags TLV (TLV 1170) of the BGP-LS IPv4/IPv6
   Prefix NLRI Attribute as defined in section 2.3.2 of
   [I-D.ietf-idr-bgp-ls-segment-routing-ext].



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   The ERLD MSD-type introduced for OSPF in Section 4 is advertised
   using the Node MSD TLV (TLV 266) of the BGP-LS Node NLRI Attribute as
   defined in section 3 of [I-D.ietf-idr-bgp-ls-segment-routing-msd].

6.  Acknowledgements

   The authors would like to thank Yimin Shen, George Swallow, Acee
   Lindem, Les Ginsberg, Ketan Talaulikar, Jeff Tantsura , Bruno
   Decraene and Carlos Pignataro for their valuable comments.

7.  IANA Considerations

   This document requests IANA to allocate one flag from the OSPFv2
   Extended Prefix TLV Flags registry:

      0x20 - E-Flag (ELC Flag)

   This document requests IANA to allocate one flag from the OSPFv3
   Prefix Options registry:

      0x04 - E-Flag (ELC Flag)

8.  Security Considerations

   The security considerations as described in [RFC7770] and
   [I-D.ietf-mpls-spring-entropy-label] are applicable to this document.

   Incorrectly setting the E flag (ELC capable) (during origination,
   inter-area advertisement or redistribution) may lead to black-holing
   of the traffic on the egress node.

   Incorrectly setting of the ERLD value may lead to poor load-balancing
   of the traffic.

9.  Contributors

   The following people contributed to the content of this document and
   should be considered as co-authors:













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      Gunter Van de Velde (editor)
      Nokia
      Antwerp
      BE

      Email: gunter.van_de_velde@nokia.com


      Wim Henderickx
      Nokia
      Belgium

      Email: wim.henderickx@nokia.com

      Keyur Patel
      Arrcus
      USA

      Email: keyur@arrcus.com


10.  References

10.1.  Normative References

   [BCP14]    , <https://tools.ietf.org/html/bcp14>.

   [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-idr-bgp-ls-segment-routing-msd]
              Tantsura, J., Chunduri, U., Talaulikar, K., Mirsky, G.,
              and N. Triantafillis, "Signaling MSD (Maximum SID Depth)
              using Border Gateway Protocol Link-State", draft-ietf-idr-
              bgp-ls-segment-routing-msd-09 (work in progress), October
              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-10 (work in progress), October 2019.






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   [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-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>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [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>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [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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   [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>.

10.2.  Informative References

   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-27 (work in progress), December 2018.

Authors' Addresses

   Xiaohu Xu
   Alibaba Inc

   Email: xiaohu.xxh@alibaba-inc.com


   Sriganesh Kini

   Email: sriganeshkini@gmail.com


   Peter Psenak
   Cisco Systems, Inc.
   Eurovea Centre, Central 3
   Pribinova Street 10
   Bratislava  81109
   Slovakia

   Email: ppsenak@cisco.com


   Clarence Filsfils
   Cisco Systems, Inc.
   Brussels
   Belgium

   Email: cfilsfil@cisco.com









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   Stephane Litkowski
   Cisco Systems, Inc.
   La Rigourdiere
   Cesson Sevigne
   France

   Email: slitkows@cisco.com


   Matthew Bocci
   Nokia
   Shoppenhangers Road
   Maidenhead, Berks
   UK

   Email: matthew.bocci@nokia.com



































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