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Versions: 00 01 02 03 04 05 draft-ietf-idr-bgp-ls-segment-routing-msd

IDR Working Group                                            J. Tantsura
Internet-Draft                                               U. Chunduri
Intended status: Standards Track                               G. Mirsky
Expires: July 14, 2017                                        Individual
                                                            S. Sivabalan
                                                                   Cisco
                                                        January 10, 2017


  Signaling Maximum SID Depth using Border Gateway Protocol Link-State
            draft-tantsura-idr-bgp-ls-segment-routing-msd-02

Abstract

   This document discusses use of BGP-LS to expose node and/or link on a
   node MSD "Maximum SID Depth" to a centralized controller (PCE/SDN).

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
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   This Internet-Draft will expire on July 14, 2017.

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   Copyright (c) 2017 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions used in this document . . . . . . . . . . . .   2
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   2
       1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   3
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   3.  MSD supported by a node . . . . . . . . . . . . . . . . . . .   3
   4.  MSD supported on a link . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   When Segment Routing tunnels are computed by a centralized
   controller, it is crucial that the controller knows MSD "Maximum SID
   Depth" of the node or link SR tunnel exits over, so it doesn't
   download a path with SID (label stack) of a depth more than the node
   or link configured is capable of imposing.This document describes how
   to use BGP-LS to expose the MSD of the node or link configured to a
   centralized controller.

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






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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]

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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     MSD       |
     +-+-+-+-+-+-+-+-+

                      Figure 1: Node attribute format

   Type : A 2-octet field specifiying code-point of the new TLV type.
   Code-point: TBA (suggested 1050) 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

   MSD: Node MSD is a number in the range of 0-254.  The vaule of 0
   represents lack of ability to push MSD of any depth, any other value
   represents that of the node.







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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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     MSD       |
     +-+-+-+-+-+-+-+-+

                      Figure 2: Link attribute format

   Type : A 2-octet field specifiying code-point of the new TLV type.
   Code-point: TBA (suggested 1110) 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

   MSD: Link MSD is a number in the range of 0-254.  The vaule of 0
   represents lack of ability to push MSD of any depth, any other value
   represents that of the link.

5.  IANA Considerations

   This document requests assigning 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 for the valuable comments.

8.  References

8.1.  Normative References







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   [I-D.ietf-isis-segment-routing-msd]
              Tantsura, J. and U. Chunduri, "Signaling MSD (Maximum SID
              Depth) using IS-IS", draft-ietf-isis-segment-routing-
              msd-00 (work in progress), November 2016.

   [I-D.ietf-ospf-segment-routing-msd]
              Tantsura, J. and U. Chunduri, "Signaling MSD (Maximum SID
              Depth) using OSPF", draft-ietf-ospf-segment-routing-msd-00
              (work in progress), November 2016.

   [I-D.ietf-pce-segment-routing]
              Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E.,
              Raszuk, R., Lopez, V., Tantsura, J., Henderickx, W., and
              J. Hardwick, "PCEP Extensions for Segment Routing", draft-
              ietf-pce-segment-routing-08 (work in progress), October
              2016.

   [I-D.ietf-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Shakir, R.,
              jefftant@gmail.com, j., and E. Crabbe, "Segment Routing
              with MPLS data plane", draft-ietf-spring-segment-routing-
              mpls-05 (work in progress), July 2016.

   [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-09 (work in progress), October
              2016.








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   [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-10 (work in progress), October 2016.

Authors' Addresses

   Jeff Tantsura
   Individual

   Email: jefftant.ietf@gmail.com


   Uma Chunduri
   Individual

   Email: uma.chunduri@gmail.com


   Greg Mirsky
   Individual

   Email: gregimirsky@gmail.com


   Siva Sivabalan
   Cisco

   Email: msiva@cisco.com





















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