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Versions: 00 01 02                                                      
IDR Working Group                                            J. Tantsura
Internet-Draft                                                 G. Mirsky
Intended status: Standards Track                                Ericsson
Expires: January 7, 2016                                    July 6, 2015


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

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).

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   This Internet-Draft will expire on January 7, 2016.

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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 . . . . . . . . . . . . . . . . . . .   3
   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  . . . . . . . . . . . . . . . . . . . . . . .   5

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 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.

3.  MSD supported by a node

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

   Node MSD is encoded in the Opaque Node Attribute TLV, as defined in
   [I-D.ietf-idr-ls-distribution]

      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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //               Opaque node attributes (variable)             //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 1: Opaque Node attribute format

4.  MSD supported on a link

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

   Link MSD is encoded in the Opaque Link Attribute TLV, as defined in
   [I-D.ietf-idr-ls-distribution]









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      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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                Opaque link attributes (variable)            //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 2: Opaque link attribute format

5.  IANA Considerations

   TBA

6.  Security Considerations

   This document does not introduce security issues beyond those
   discussed in [I-D.ietf-idr-ls-distribution]

7.  Acknowledgements

   We like to thank Nikos Triantafillis for the valuable comments.

8.  References

8.1.  Normative References

   [I-D.ietf-idr-ls-distribution]
              Gredler, H., Medved, J., Previdi, S., Farrel, A., and S.
              Ray, "North-Bound Distribution of Link-State and TE
              Information using BGP", draft-ietf-idr-ls-distribution-11
              (work in progress), June 2015.

   [I-D.ietf-pce-segment-routing]
              Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E.,
              Lopez, V., Tantsura, J., Henderickx, W., and J. Hardwick,
              "PCEP Extensions for Segment Routing", draft-ietf-pce-
              segment-routing-05 (work in progress), May 2015.

   [I-D.ietf-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J.,
              and E. Crabbe, "Segment Routing with MPLS data plane",
              draft-ietf-spring-segment-routing-mpls-01 (work in
              progress), May 2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.



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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. Tantsura, "IS-IS
              Extensions for Segment Routing", draft-ietf-isis-segment-
              routing-extensions-05 (work in progress), June 2015.

   [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-05 (work in progress), June 2015.

Authors' Addresses

   Jeff  Tantsura
   Ericsson

   Email: jeff.tantsura@ericsson.com


   Greg Mirsky
   Ericsson

   Email: gregory.mirsky@ericsson.com

























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