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Versions: (draft-tantsura-idr-bgp-ls-segment-routing-msd) 00

IDR Working Group                                            J. Tantsura
Internet-Draft                                                Individual
Intended status: Standards Track                             U. Chunduri
Expires: January 18, 2018                            Huawei Technologies
                                                               G. Mirsky
                                                               ZTE Corp.
                                                            S. Sivabalan
                                                                   Cisco
                                                           July 17, 2017


  Signaling Maximum SID Depth using Border Gateway Protocol Link-State
              draft-ietf-idr-bgp-ls-segment-routing-msd-00

Abstract

   This document proposes a way to signal Maximum SID Depth (MSD)
   supported by a node at node and/or link granularity by a BGP-LS
   speaker.  In a Segment Routing (SR) enabled network a centralized
   controller that programs SR tunnels needs to know the MSD supported
   by the head-end at node and/or link granularity to push the SID stack
   of an appropriate depth.  MSD is relevant to the head-end of a SR
   tunnel or Binding-SID anchor node where Binding-SID expansions might
   result in creation of a new SID stack.

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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   This Internet-Draft will expire on January 18, 2018.

Copyright Notice

   Copyright (c) 2017 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
   (http://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
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   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
       1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   3
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   3.  MSD supported by a node . . . . . . . . . . . . . . . . . . .   4
   4.  MSD supported on a link . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   When Segment Routing tunnels are computed by a centralized
   controller, it is critical that the controller learns the MSD
   "Maximum SID Depth" of the node or link SR tunnel exits over, so the
   SID stack depth of a path computed doesn't exceed the number of SIDs
   the node is capable of imposing.  This document describes how to use
   BGP-LS to signal the MSD of a node or link to a centralized
   controller.

   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 of sub-type 1, called Base MSD as defined in Section 3 is used to
   signal the number of SID's a node is capable of imposing, to be used



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   by a path computation element/controller.  In case, there are
   additional labels (e.g. service) that are to be pushed to the stack -
   this would be signaled with an another MSD type (TBD), no adjustment
   to the Base MSD should be made.  In the future, new MSD types could
   be defined to signal additional capabilities: entropy labels, labels
   that can be pushed thru recirculation, or 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

   MSD: Maximum SID Depth

   PCC: Path Computation Client

   PCE: Path Computation Element

   PCEP: Path Computation Element Protocol

   SID: Segment Identifier

   SR: Segment routing

1.1.2.  Requirements Language

   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
   [RFC2119].

2.  Problem Statement

   In existing technology only PCEP has extension to signal the MSD (SR
   PCE Capability TLV/ METRIC Object as defined in
   [I-D.ietf-pce-segment-routing],If PCEP is not supported by the node
   (head-end of the SR tunnel) controller has no way to learn the MSD of
   the node/link configured.  OSPF and IS-IS extensions are defined in:

   [I-D.ietf-ospf-segment-routing-msd]

   [I-D.ietf-isis-segment-routing-msd]







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3.  MSD supported by a node

   Node MSD is encoded in a new Node Attribute TLV, as defined in
   [RFC7752]

      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 attribute format

   Type : A 2-octet field specifiying code-point of the new TLV type.
   Code-point:(to be assigned by IANA) from BGP-LS Node Descriptor, Link
   Descriptor, Prefix Descriptor, and Attribute TLVs registry

   Length: A 2-octet field that indicates the length of the value
   portion

   Sub-Type and value fields are as defined in corresponding OSPF
   [I-D.ietf-ospf-segment-routing-msd] and IS-IS
   [I-D.ietf-isis-segment-routing-msd] extensions.

4.  MSD supported on a link

   Link MSD is encoded in a New Link Attribute TLV, as defined in
   [RFC7752]

      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 attribute format

   Type : A 2-octet field specifiying code-point of the new TLV type.
   Code-point:(to be assigned by IANA) from BGP-LS Node Descriptor, Link
   Descriptor, Prefix Descriptor, and Attribute TLVs registry

   Length: A 2-octet field that indicates the length of the value
   portion




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   Sub-Type and value fields are as defined in corresponding OSPF
   [I-D.ietf-ospf-segment-routing-msd] and IS-IS
   [I-D.ietf-isis-segment-routing-msd] extensions.

5.  IANA Considerations

   This document requests IANA to assign 2 new code-points from the BGP-
   LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
   TLVs registry as specified in sections 3 and 4.

6.  Security Considerations

   This document does not introduce security issues beyond those
   discussed in [RFC7752]

7.  Acknowledgements

   We like to thank Nikos Triantafillis, Stephane Litkowski and Bruno
   Decraene for their reviews and valuable comments.

8.  References

8.1.  Normative References

   [I-D.ietf-isis-segment-routing-msd]
              Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling MSD (Maximum SID Depth) using IS-IS", draft-
              ietf-isis-segment-routing-msd-04 (work in progress), June
              2017.

   [I-D.ietf-ospf-segment-routing-msd]
              Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
              "Signaling MSD (Maximum SID Depth) using OSPF", draft-
              ietf-ospf-segment-routing-msd-05 (work in progress), June
              2017.

   [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-09 (work in progress),
              April 2017.

   [I-D.ietf-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing with MPLS
              data plane", draft-ietf-spring-segment-routing-mpls-10
              (work in progress), June 2017.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [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,
              <http://www.rfc-editor.org/info/rfc7752>.

8.2.  Informative References

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
              Litkowski, S., Decraene, B., and j. jefftant@gmail.com,
              "IS-IS Extensions for Segment Routing", draft-ietf-isis-
              segment-routing-extensions-13 (work in progress), June
              2017.

   [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-17 (work in progress), June 2017.

Authors' Addresses

   Jeff Tantsura
   Individual

   Email: jefftant.ietf@gmail.com


   Uma Chunduri
   Huawei Technologies

   Email: uma.chunduri@huawei.com


   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com







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   Siva Sivabalan
   Cisco

   Email: msiva@cisco.com















































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