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Versions: (draft-tantsura-ospf-segment-routing-msd) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 RFC 8476

OSPF Working Group                                           J. Tantsura
Internet-Draft                                            Nuage Networks
Intended status: Standards Track                             U. Chunduri
Expires: August 30, 2018                             Huawei Technologies
                                                               S. Aldrin
                                                             Google, Inc
                                                               P. Psenak
                                                           Cisco Systems
                                                       February 26, 2018


              Signaling MSD (Maximum SID Depth) using OSPF
                 draft-ietf-ospf-segment-routing-msd-09

Abstract

   This document defines a way for an OSPF Router to advertise multiple
   types of supported Maximum SID Depths (MSDs) at node and/or link
   granularity.  Such advertisements allow entities (e.g., centralized
   controllers) to determine whether a particular SID stack is
   supportable in a given network.  This document only defines one type
   of MSD (maximum label imposition) - but defines an encoding which can
   support other MSD types.  Here the term OSPF means both OSPFv2 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
   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 August 30, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions used in this document . . . . . . . . . . . .   3
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Node MSD TLV  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Link MSD sub-TLV  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Using Node and Link MSD Advertisements  . . . . . . . . . . .   5
   6.  Base MPLS Imposition MSD  . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     11.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   When Segment Routing(SR) paths are computed by a centralized
   controller, it is critical that the controller learns the Maximum SID
   Depth(MSD) which can be imposed at the node/link a given SR path is
   applied so as to insure that the SID stack depth of a computed path
   doesn't exceed the number of SIDs the node is capable of imposing.

   PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD
   in SR PCE Capability TLV and METRIC Object.  However, if PCEP is not
   supported/configured on the head-end of a SR tunnel or a Binding-SID
   anchor node and controller does not participate in IGP routing, it
   has no way to learn the MSD of nodes and links which has been
   configured.  BGP-LS [RFC7752] defines a way to expose topology and
   associated attributes and capabilities of the nodes in that topology
   to a centralized controller.  MSD signaling by BGP-LS has been
   defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd].  Typically,
   BGP-LS is configured on a small number of nodes, that do not



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   necessarily act as head-ends.  In order, for BGP-LS to signal MSD for
   all the nodes and links in the network MSD is relevant, MSD
   capabilites should be advertised to every OSPF router in the network.

   Other types of MSD are known to be useful.  For example,
   [I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability
   (RLDC) that is used by a head-end to insert Entropy Label (EL) at
   appropriate depth, so it could be read by transit nodes.

   This document defines an extension to OSPF used to advertise one or
   more types of MSD at node and/or link granularity.  It also creates
   an IANA registry for assigning MSD type identifiers.  It also defines
   one MSD type called Base MPLS Imposition MSD.  In the future it is
   expected that new MSD types will be defined to signal additional
   capabilities e.g., entropy labels, SIDs that can be imposed through
   recirculation, or SIDs associated with another dataplane e.g., IPv6.

1.1.  Conventions used in this document

1.1.1.  Terminology

   BGP-LS: Distribution of Link-State and TE Information using Border
   Gateway Protocol

   BMI: Base MPLS Imposition is the number of MPLS labels which can be
   imposed inclusive of any service/transport labels

   OSPF: Open Shortest Path First

   MSD: Maximum SID Depth - the number of SIDs a node or a link on a
   node can support

   PCC: Path Computation Client

   PCE: Path Computation Element

   PCEP: Path Computation Element Protocol

   SID: Segment Identifier

   SR: Segment Routing

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].




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2.  Terminology

   This memo makes use of the terms defined in [RFC4970].

3.  Node MSD TLV

   A new TLV within the body of the OSPF RI Opaque LSA, called Node MSD
   TLV is defined to carry the provisioned SID depth of the router
   originating the RI LSA.  Node MSD is the lowest MSD supported by the
   node.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Type                       |         Length                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Sub-Type and Value ...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...


                          Figure 1: Node MSD TLV

   The Type (2 bytes) of this TLV has value of 12.

   Length is variable (minimum of 2, multiple of 2 octets) and
   represents the total length of value field.

   Value field consists of a 1 octet sub-type (IANA Registry) and 1
   octet value.

   Sub-Type 1 (IANA Section), MSD and the Value field contains maximum
   MSD of the router originating the RI LSA.  Node Maximum MSD is a
   number in the range of 0-254. 0 represents lack of the ability to
   impose MSD stack of any depth; any other value represents that of the
   node.  This value SHOULD represent the lowest value supported by
   node.

   Other Sub-types other than defined above are reserved for future
   extensions.

   This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is
   optional.  The scope of the advertisement is specific to the
   deployment.







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4.  Link MSD sub-TLV

   A new sub-TLV called Link MSD sub-TLV is defined to carry the
   provisioned SID depth of the interface associated with the link.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Type                       |         Length                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Sub-Type and Value ...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...


                        Figure 2: Link MSD Sub-TLV

   The Type (2 bytes) of this TLV:

   For OSPFv2, the Link level MSD value is advertised as an optional
   Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684], and has
   value of 6.

   For OSPFv3, the Link level MSD value is advertised as an optional
   Sub-TLV of the Router-Link TLV as defined in
   [I-D.ietf-ospf-ospfv3-lsa-extend], and has value of 16 (Suggested
   value - to be assigned by IANA).

   Length is variable and similar to what is defined in Section 3.

   Value field consists of a 1 octet sub-type (IANA Registry) and 1
   octet value.

   Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD
   of the router originating the corresponding LSA as specified for
   OSPFv2 and OSPFv3.  Link MSD is a number in the range of 0-254. 0
   represents lack of the ability to impose MSD stack of any depth; any
   other value represents that of the particular link MSD value.

   Other Sub-types other than defined above are reserved for future
   extensions.

5.  Using Node and Link MSD Advertisements

   When Link MSD is present for a given MSD type, the value of the Link
   MSD MUST be used in preference to the Node MSD.





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   The meaning of the absence of both Node and Link MSD advertisements
   for a given MSD type is specific to the MSD type.  Generally it can
   only be inferred that the advertising node does not support
   advertisement of that MSD type.  However, in some cases the lack of
   advertisement might imply that the functionality associated with the
   MSD type is not supported.  The correct interpretation MUST be
   specified when an MSD type is defined.

6.  Base MPLS Imposition MSD

   Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS
   labels a node is capable of imposing, including any service/transport
   labels.

   Absence of BMI-MSD advertisements indicates only that the advertising
   node does not support advertisement of this capability.

7.  IANA Considerations

   This document includes a request to IANA to allocate TLV type codes
   for the new TLV proposed in Section 3 of this document from OSPF
   Router Information (RI) TLVs Registry as defined by [RFC4970].  For
   the link MSD, we request IANA to allocate new sub-TLV codes as
   proposed in Section 4 from OSPFv2 Extended Link TLV Sub-TLVs registry
   and from Router-Link TLV defined in OSPFv3 Extend-LSA Sub-TLV
   registry.

   This document requests creation of a new IANA managed registry under
   a new category of "Interior Gateway Protocol (IGP) Parameters" IANA
   registries to identify MSD types as proposed in Section 3, Section 4.
   The registration procedure is "Expert Review" as defined in
   [RFC8126].  Suggested registry name is "MSD types".  Types are an
   unsigned 8 bit number.  The following values are defined by this
   document


              Value     Name                             Reference
              -----     ---------------------            -------------
              0         Reserved                         This document
              1         Base MPLS Imposition MSD         This document
              2-250     Unassigned                       This document
              251-254   Experimental                     This document
              255       Reserved                         This document

                  Figure 3: MSD Types Codepoints Registry






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8.  Security Considerations

   Security considerations, as specified by [RFC7770] are applicable to
   this document

9.  Contributors

   The following people contributed to this document:

   Les Ginsberg

   Email: ginsberg@cisco.com

10.  Acknowledgements

   The authors would like to thank Stephane Litkowski and Bruno Decraene
   for their reviews and valuable comments.

11.  References

11.1.  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>.

   [RFC4970]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July
              2007, <https://www.rfc-editor.org/info/rfc4970>.

   [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>.

11.2.  Informative References

   [I-D.ietf-idr-bgp-ls-segment-routing-msd]
              Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
              "Signaling Maximum SID Depth using Border Gateway Protocol
              Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01
              (work in progress), October 2017.







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   [I-D.ietf-ospf-mpls-elc]
              Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "Signaling Entropy Label Capability and
              Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
              mpls-elc-05 (work in progress), January 2018.

   [I-D.ietf-ospf-ospfv3-lsa-extend]
              Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.
              Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-
              lsa-extend-23 (work in progress), January 2018.

   [I-D.ietf-pce-segment-routing]
              Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "PCEP Extensions for Segment Routing",
              draft-ietf-pce-segment-routing-11 (work in progress),
              November 2017.

   [RFC5838]  Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
              R. Aggarwal, "Support of Address Families in OSPFv3",
              RFC 5838, DOI 10.17487/RFC5838, April 2010,
              <https://www.rfc-editor.org/info/rfc5838>.

   [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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Authors' Addresses

   Jeff Tantsura
   Nuage Networks

   Email: jefftant.ietf@gmail.com







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   Uma Chunduri
   Huawei Technologies

   Email: uma.chunduri@huawei.com


   Sam Aldrin
   Google, Inc

   Email: aldrin.ietf@gmail.com


   Peter Psenak
   Cisco Systems

   Email: ppsenak@cisco.com



































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