IDR Working Group                                            J. Tantsura
Internet-Draft                                                Individual                                            Nuage Networks
Intended status: Standards Track                             U. Chunduri
Expires: April 18, 2018 February 14, 2019                                    Huawei Technologies USA
                                                               G. Mirsky
                                                               ZTE Corp.
                                                            S. Sivabalan
                                                                   Cisco
                                                        October 15, 2017
                                                         August 13, 2018

 Signaling Maximum MSD (Maximum SID Depth Depth) using Border Gateway Protocol Link-State
              draft-ietf-idr-bgp-ls-segment-routing-msd-01 Link-
                                 State
              draft-ietf-idr-bgp-ls-segment-routing-msd-02

Abstract

   This document proposes defines a way for a Border Gateway Protocol Link-State
   (BGP-LS) speaker to signal advertise multiple types of supported Maximum SID Depth (MSD)
   supported by a node
   Depths (MSDs) at node and/or link granularity by a BGP-LS
   speaker.  In a Segment Routing (SR) enabled network a granularity.

   Such advertisements allow logically centralized
   controller that programs SR tunnels needs to know the MSD supported
   by the head-end at node and/or link granularity entities (e.g.,
   centralized controllers) to push the determine whether a particular 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
   can be supported in creation of a new SID stack. given network.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on April 18, 2018. February 14, 2019.

Copyright Notice

   Copyright (c) 2017 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Internet-DrafSignaling MSD (Maximum SID Depth) using BGP-LS  August 2018

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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   3
   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   7

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

   Other types 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, are known to be useful.  For example,
   [I-D.ietf-ospf-mpls-elc] and [I-D.ietf-isis-mpls-elc] define Readable

Internet-DrafSignaling MSD (Maximum SID Depth) using BGP-LS  August 2018

   Label Depth Capability (RLDC) that is used by a path computation element/controller.  In case, there are
   additional labels (e.g. service) that are to be pushed head-end to the stack -
   this would be signaled with insert 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
   Entropy Label (EL) at a depth that can be pushed thru recirculation, or another dataplane e.g IPv6. read by transit nodes.

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]. BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here .

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]

Internet-DrafSignaling MSD (Maximum SID Depth) using BGP-LS  August 2018

      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 specifying code-point of the new TLV type.
   Code-point:(TBD1) 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 specifying code-point of the new TLV type.
   Code-point:(TBD2) 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.

Internet-DrafSignaling MSD (Maximum SID Depth) using BGP-LS  August 2018

5.  IANA Considerations

   We request IANA assign code points from the registry BGP-LS Node
   Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs,
   as follows: TLV Code Point Description IS-IS TLV/Sub-TLV Reference
   TBD1 Node MSD 242/23 (this document) TBD2 Link MSD
   (22,23,25,141,222,223)/15 (this document)

6.  Security Considerations

   Advertisement of the additional information defined in this document
   that is false, e.g., an MSD that is incorrect, may result in a path
   computation failing, having a service unavailable, or instantiation
   of a path that can't be supported by the head-end (the node
   performing the imposition).

   This document does not introduce security issues beyond those
   discussed in [RFC7752] [RFC7752], [I-D.ietf-ospf-segment-routing-msd] and
   [I-D.ietf-isis-segment-routing-msd]

7.  Acknowledgements

   We like to thank Nikos Triantafillis, Acee Lindem, Ketan Talaulikar,
   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
              ietf-isis-segment-routing-msd-13 (work in progress), June
              2017. July
              2018.

   [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
              ietf-ospf-segment-routing-msd-15 (work in progress), June
              2017. July
              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-10
              draft-ietf-pce-segment-routing-12 (work in progress),
              October 2017. June
              2018.

Internet-DrafSignaling MSD (Maximum SID Depth) using BGP-LS  August 2018

   [I-D.ietf-spring-segment-routing-mpls]
              Bashandy, A., 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 draft-ietf-spring-segment-routing-mpls-14
              (work in progress), June 2017. 2018.

   [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>.

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

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

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., Litkowski, S., Decraene, B., and j. jefftant@gmail.com, J. Tantsura,
              "IS-IS Extensions for Segment Routing", draft-ietf-isis-
              segment-routing-extensions-13
              segment-routing-extensions-19 (work in progress), June
              2017. July
              2018.

   [I-D.ietf-ospf-mpls-elc]
              Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "Signaling Entropy Label Capability and Entropy
              Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
              mpls-elc-06 (work in progress), August 2018.

   [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-19
              routing-extensions-25 (work in progress), April 2018.

Internet-DrafSignaling MSD (Maximum SID Depth) using BGP-LS  August 2017. 2018

Authors' Addresses

   Jeff Tantsura
   Individual
   Nuage Networks

   Email: jefftant.ietf@gmail.com

   Uma Chunduri
   Huawei Technologies USA

   Email: uma.chunduri@huawei.com

   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com

   Siva Sivabalan
   Cisco

   Email: msiva@cisco.com