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Versions: (draft-tantsura-isis-segment-routing-msd) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19

IS-IS Working Group                                          J. Tantsura
Internet-Draft                                                Individual
Intended status: Standards Track                             U. Chunduri
Expires: July 14, 2018                               Huawei Technologies
                                                               S. Aldrin
                                                             Google, Inc
                                                             L. Ginsberg
                                                           Cisco Systems
                                                        January 10, 2018


             Signaling MSD (Maximum SID Depth) using IS-IS
                 draft-ietf-isis-segment-routing-msd-09

Abstract

   This document defines a way for an IS-IS 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.

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
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   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 July 14, 2018.

Copyright Notice

   Copyright (c) 2018 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
   Provisions Relating to IETF Documents



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   (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.  Node MSD Advertisement  . . . . . . . . . . . . . . . . . . .   4
   3.  Link MSD Advertisement  . . . . . . . . . . . . . . . . . . .   4
   4.  Using Node and Link MSD Advertisements  . . . . . . . . . . .   5
   5.  Base MPLS Imposition MSD  . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   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
   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




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   capabilites should be advertised to every IS-IS router in the
   network.

   Other types of MSD are known to be useful.  For example,
   [I-D.ietf-isis-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 IS-IS 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

   IS-IS: Intermediate System to Intermediate System

   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.  Node MSD Advertisement

   A new sub-TLV "Node MSD sub-TLV" is defined within the body of the
   IS-IS Router Capability TLV [RFC7981], to carry the provisioned
   MSD(s) of the router originating the Router Capability TLV.  Node MSD
   is the lowest MSD supported by the node on any interface.  MSD values
   may be learned via a hardware API or may be provisioned.

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

         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |    Type       |   Length      |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |   MSD-Type    | MSD Value     |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         //     ...................     //
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |   MSD-Type    | MSD Value     |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                        Figure 1: Node MSD Sub-TLV

   The Type (1 byte) of this sub-TLV has value of 23.

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

   Value field consists of one or more pairs of a 1 octet MSD-Type (IANA
   Registry) and 1 octet Value.

   Node MSD value is a number in the range of 0-255. 0 represents lack
   of the ability to support SID stack of any depth; any other value
   represents that of the node.  This value MUST represent the lowest
   value supported by any link associated with the node.

   This sub-TLV is optional.  The scope of the advertisement is specific
   to the deployment.

3.  Link MSD Advertisement

   A new sub-TLV - Link MSD sub-TLV is defined for TLVs 22, 23, 141,
   222, and 223 to carry the MSD of the interface associated with the
   link.  MSD values may be learned via a hardware API or may be
   provisioned.





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

         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |    Type       |   Length      |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |   MSD-Type    | MSD Value     |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         //     ...................     //
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |   MSD-Type    | MSD Value     |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                        Figure 2: Link MSD Sub-TLV

   The Type (1 byte) of this sub-TLV has value of 15.

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

   Value field consists of one or more pairs of a 1 octet MSD-Type (IANA
   Registry) and 1 octet Value.

   Link MSD value is a number in the range of 0-255. 0 represents lack
   of the ability to support SID stack of any depth; any other value
   represents that of the link when used as an outgoing link.

   This sub-TLV is optional.  The scope of the advertisement is specific
   to the deployment.

4.  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.

   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.








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5.  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.

6.  IANA Considerations

   This document requests IANA to allocate a sub-TLV type code for the
   new sub TLV proposed in Section 2 of this document from IS-IS Router
   Capability TLV Registry as defined by [RFC7981].

   The following value has been allocated by IANA:


      Value     Description                      Reference
      -----     ---------------                  -------------
      23        Node MSD                         This document

                            Figure 3: Node MSD

   This document requests IANA to allocate a sub-TLV type code as
   defined in Section 3 from Sub-TLVs for TLVs 22, 23, 141, 222 and 223
   registry.

   The following value has been allocated by IANA:


      Value     Description                      Reference
      -----     ---------------                  -------------
      15        Link MSD                         This document

                            Figure 4: Link MSD

   Per TLV information where Link MSD sub-TLV can be part of:


      TLV  22 23 25 141 222 223
      ---  --------------------
           y  y  y  y   y   y

           Figure 5: TLVs where LINK MSD Sub-TLV can be present

   This document requests creation of a new IANA managed registry under
   a new category of "Interior Gateway Protocol (IGP) Parameters" IANA



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   registries to identify MSD types as proposed in Section 2 and
   Section 3.  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 6: MSD Types Codepoints Registry

7.  Security Considerations

   Security considerations, as specified by [RFC7981] are applicable to
   this document

8.  Contributors

   The following people contributed to this document:

   Peter Psenak

   Email: ppsenak@cisco.com

9.  Acknowledgements

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

10.  References

10.1.  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>.

   [RFC7981]  Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
              for Advertising Router Information", RFC 7981,
              DOI 10.17487/RFC7981, October 2016,
              <https://www.rfc-editor.org/info/rfc7981>.



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10.2.  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.

   [I-D.ietf-isis-mpls-elc]
              Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "Signaling Entropy Label Capability and
              Readable Label-stack Depth Using IS-IS", draft-ietf-isis-
              mpls-elc-03 (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.

   [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
   Individual

   Email: jefftant.ietf@gmail.com


   Uma Chunduri
   Huawei Technologies

   Email: uma.chunduri@huawei.com








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   Sam Aldrin
   Google, Inc

   Email: aldrin.ietf@gmail.com


   Les Ginsberg
   Cisco Systems

   Email: ginsberg@cisco.com









































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