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Versions: (draft-tantsura-ospf-segment-routing-msd) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 RFC 8476

OSPF Working Group                                           J. Tantsura
Internet-Draft                                               U. Chunduri
Intended status: Standards Track                              Individual
Expires: May 20, 2017                                  November 16, 2016


              Signaling MSD (Maximum SID Depth) using OSPF
                 draft-ietf-ospf-segment-routing-msd-00

Abstract

   This document proposes a way to expose Maximum SID Depth (MSD)
   supported by a node at node and/or link level by an OSPF Router.  In
   a Segment Routing (SR) enabled network a centralized controller that
   programs SR tunnels at the head-end node needs to know the MSD
   information at node level and/or link level to push the label stack
   of an appropriate depth .  Here the term OSPF means both OSPFv2 and
   OSPFv3.

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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   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 May 20, 2017.

Copyright Notice

   Copyright (c) 2016 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
   (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
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Node MSD TLV  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  LINK MSD sub-TLV  . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Node MSD vs Link MSD conflict resolution  . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  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 the 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 used is capable of imposing.  This document describes how to
   use OSPF to expose the MSD of the node or link to a centralized
   controller.

   PCEP SR extensions [I-D.ietf-pce-segment-routing] has defined MSD, to
   signal in SR PCE Capability TLV, METRIC Object.  However, If PCEP is
   not supported by a node (head-end of the SR tunnel) and controller
   does not participate in IGP routing it has no way to learn the MSD of
   the node or link configured.  BGP-LS [RFC7752] defines a way to
   expose topology and associated different attributes, capabilities of
   the nodes in that topology to a centralized controller and MSD has
   been defined in [I-D.tantsura-bgp-ls-segment-routing-msd].  For this
   information to be advertised by BGP for the all nodes and links of
   the network, where this is provisioned, OSPF module should have this
   information in the LSDB.

   [I-D.ietf-ospf-mpls-elc] defines, RLSDC which indicates how many
   labels a node can read to take a decision to insert an Entropy Label
   (EL) and is different than how many labels a node can push as defined
   by MSD in this draft.




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1.1.  Conventions used in this document

1.1.1.  Terminology

   BGP-LS: Distribution of Link-State and TE Information using Border
   Gateway Protocol

   OSPF: Open Shortest Path First

   MSD: Maximum SID Depth

   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].

2.  Terminology

   This memo makes use of the terms defined in [RFC4970].

3.  Node MSD TLV

   A new TLV within the body of the OSPF RI Opaque LSA, called Node MSD
   TLV is defined to carry the provisioned SID depth of the router
   originating the RI LSA.  Node MSD is the lowest MSD supported by the
   node.

   The Type (2 bytes) of this TLV is TBD.

   Length is 2 bytes, and

   the Value field contains MSD of the router originating the RI LSA.
   Node MSD is a number in the range of 0-254. 0 represents lack of the
   ability to push MSD of any depth; any other value represents that of
   the node.  This value SHOULD represent the lowest value supported by
   node.




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   This TLV is applicable to OSPFv2 and to OSPFv3 [RFC5838] and is
   optional.  The scope of the advertisement is specific to the
   deployment.

4.  LINK MSD sub-TLV

   A new sub-TLV called Link MSD sub-TLV is defined to carry the
   provisioned SID depth of the interface associated with the link.

   The Type (2 bytes) of this TLV is TBD.

   Length is 2 bytes, and

   the Value field contains Link MSD of the router originating the
   corresponding LSA as specified for OSPFv3 and OSPFv3.  Link MSD is a
   number in the range of 0-254. 0 represents lack of the ability to
   push MSD of any depth; any other value represents that of the
   particular link MSD value.

   For OSPFv2, the Link level MSD value is advertised as an optional
   Sub-TLV of OSPFv2 Extended Link TLV as defined in [RFC7684].

   For OSPFv3, the Link level MSD value is advertised as an optional
   Sub-TLV of the Router-Link TLV as defined in
   [I-D.ietf-ospf-ospfv3-lsa-extend].

5.  Node MSD vs Link MSD conflict resolution

   When both Node MSD and Link MSD are present, the value in the Link
   MSD MUST be used.

6.  Acknowledgements

   TBD

7.  IANA Considerations

   This document includes a request to IANA to allocate TLV type codes
   for the new TLV proposed in Section 3 of this document from OSPF
   Router Information (RI) TLVs Registry as defined by [RFC4970].  Also
   for link MSD, we request IANA to allocate new sub-TLV codes as
   proposed in Section 4 from OSPFv2 Extended Link Opaque LSAs Extended
   Link TLV registry and from Router-Link TLV defined in OSPFv3 Extend-
   LSA Sub-TLV registry.







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8.  Security Considerations

   This document describes a mechanism for advertising Segment Routing
   SID depth supported at node and link level information through OSPF
   LSAs and does not introduce any new security issues.

9.  References

9.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4970]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July
              2007, <http://www.rfc-editor.org/info/rfc4970>.

9.2.  Informative References

   [I-D.ietf-ospf-mpls-elc]
              Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "Signaling Entropy Label Capability Using
              OSPF", draft-ietf-ospf-mpls-elc-03 (work in progress),
              October 2016.

   [I-D.ietf-ospf-ospfv3-lsa-extend]
              Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
              LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-13
              (work in progress), October 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.tantsura-bgp-ls-segment-routing-msd]
              Tantsura, J., Mirsky, G., Sivabalan, S., and U. Chunduri,
              "Signaling Maximum SID Depth using Border Gateway Protocol
              Link-State", draft-tantsura-bgp-ls-segment-routing-msd-02
              (work in progress), January 2016.






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   [RFC5838]  Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
              R. Aggarwal, "Support of Address Families in OSPFv3",
              RFC 5838, DOI 10.17487/RFC5838, April 2010,
              <http://www.rfc-editor.org/info/rfc5838>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <http://www.rfc-editor.org/info/rfc7684>.

   [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>.

Authors' Addresses

   Jeff Tantsura
   Individual

   Email: jefftant.ietf@gmail.com


   Uma Chunduri
   Individual

   Email: uma.chunduri@gmail.com























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