OSPF Working Group                                           J. Tantsura
Internet-Draft                                            Nuage Networks
Intended status: Standards Track                             U. Chunduri
Expires: August 30, October 7, 2018                             Huawei Technologies
                                                               S. Aldrin
                                                             Google, Inc
                                                               P. Psenak
                                                           Cisco Systems
                                                       February 26,
                                                          April 05, 2018

              Signaling MSD (Maximum SID Depth) using OSPF
                 draft-ietf-ospf-segment-routing-msd-09
                 draft-ietf-ospf-segment-routing-msd-10

Abstract

   This document defines a way for an OSPF Router to advertise multiple
   types of supported Maximum SID Depths (MSDs) at node and/or link
   granularity.  Such advertisements allow entities (e.g., centralized
   controllers) to determine whether a particular SID stack is
   supportable can be
   supported in a given network.  This document only defines one type of
   MSD (maximum maximum label imposition) - imposition, but defines an encoding which can
   support other MSD types.  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
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   This Internet-Draft will expire on August 30, October 7, 2018.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions used in this document . . . . . . . . . . . .   3
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Node MSD TLV  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Link MSD sub-TLV  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Using Node and Link MSD Advertisements  . . . . . . . . . . .   5
   6.  Base MPLS Imposition MSD  . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     11.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   When Segment Routing(SR) paths are computed by a centralized
   controller, it is critical that the controller learns the Maximum SID
   Depth(MSD) which that can be imposed at the each node/link a given SR path is
   applied so as to
   insure that the SID stack depth of a computed path doesn't exceed the
   number of SIDs the node is capable of imposing.

   The 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 an 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 signaling by BGP-LS has
   been defined in [I-D.ietf-idr-bgp-ls-segment-routing-msd].
   Typically, BGP-LS is configured on a small number of nodes, nodes that do
   not necessarily act as head-ends.  In order, order for BGP-LS to signal MSD
   for all the nodes and links in the network MSD is relevant, MSD
   capabilites should be advertised to every OSPF router in the network.

   Other types of MSD are known to be useful.  For example,
   [I-D.ietf-ospf-mpls-elc] defines Readable Label Depth Capability
   (RLDC) that is used by a head-end to insert an Entropy Label (EL) at
   appropriate depth, so it could
   a depth that can be read by transit nodes.

   This document defines an extension to OSPF used to advertise one or
   more types of MSD at node and/or link granularity.  It also creates
   an IANA registry for assigning MSD type identifiers.  It also laso defines
   one MSD type called
   the Base MPLS Imposition MSD. MSD type.  In the future it is
   expected expected,
   that new MSD types will be defined to signal additional capabilities
   e.g., entropy labels, SIDs that can be imposed through recirculation,
   or SIDs associated with 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

   BMI: Base MPLS Imposition is the number of MPLS labels which that can be
   imposed inclusive of any service/transport labels

   OSPF: Open Shortest Path First

   MSD: Maximum SID Depth - the number of SIDs a node or a link on a
   node one of its
   links can support

   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", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
   BCP14 [RFC2119], [RFC8174] when, and only when they appear in all
   capitals, as shown here .

2.  Terminology

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

3.  Node MSD TLV

   A new

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

        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 MSD TLV

   The Type (2 bytes) of this TLV has value of 12.

   Length is Type: TBD1

   Length: variable (minimum of 2, multiple of 2 octets) and represents
   the total length of value field.

   Value field

   Value: consists of a 1 octet sub-type (IANA Registry) and 1 octet
   value.

   Sub-Type 1 (IANA Section), MSD and the Value field contains maximum
   MSD of the router originating the RI LSA.  Node Maximum MSD is a
   number in the range of 0-254. 0 represents lack of the ability to
   impose MSD stack of any depth; any other value represents that of the
   node.  This value SHOULD represent the lowest minimum value supported by a
   node.

   Other Sub-types other than defined above are reserved for future
   extensions.

   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.

        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 MSD Sub-TLV

   The Type (2 bytes) of this TLV:

   Type:

   For OSPFv2, the Link level MSD value is advertised as an optional
   Sub-TLV of the OSPFv2 Extended Link TLV as defined in [RFC7684], and
   has value of 6. TBD2.

   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], and has value of 16 (Suggested
   value - to be assigned by IANA).

   Length is TBD3.

   Length: variable and similar to what is defined in Section 3.

   Value field

   Value: consists of a 1 octet sub-type (IANA Registry) and 1 octet
   value.

   Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD
   of the router originating the corresponding LSA as specified for
   OSPFv2 and OSPFv3.  Link MSD is a number in the range of 0-254. 0
   represents lack of the ability to impose MSD stack of any depth; any
   other value represents that of the particular link MSD value.

   Other Sub-types other than defined above are reserved for future
   extensions.

5.  Using Node and Link MSD Advertisements

   When Link MSD is present for a given MSD type, the value of the Link
   MSD MUST be used in take preference to over the Node MSD.

   The meaning of the absence of both Node and Link MSD advertisements
   for a given MSD type is specific to the MSD type.  Generally it can
   only be inferred that the advertising node does not support
   advertisement of that MSD type.  However, in some cases the lack of
   advertisement might imply that the functionality associated with the
   MSD type is not supported.  The correct interpretation MUST be
   specified when an MSD type is defined.

6.  Base MPLS Imposition MSD

   The Base MPLS Imposition MSD (BMI-MSD) signals the total number of
   MPLS labels a node is capable of imposing, including any service/transport service/
   transport labels.

   Absence of BMI-MSD advertisements indicates only solely that the
   advertising node does not support advertisement of this capability.

7.  IANA Considerations

   This document includes a request to requests IANA to allocate TLV type codes
   for the new TLV proposed in Section 3 of this document (TBD1) from the OSPF
   Router Information (RI) TLVs Registry as defined by [RFC4970].  For  IANA
   has allocated the link MSD, we request value 12 through the early assignment process.
   Also, this document requests IANA to allocate new a sub-TLV codes as
   proposed in Section 4 type (TBD2)
   from the OSPFv2 Extended Link TLV Sub-TLVs registry
   and registry.  IANA has
   allocated the the value 6 through the early assignment process.
   Finally, this document requests IANA to allocate a sub-TLV type
   (TBD3) from Router-Link TLV defined in the OSPFv3 Extend-LSA Extended-LSA Sub-TLV registry.

   This document requests creation of a new an IANA managed registry under a
   new category of "Interior Gateway Protocol (IGP) Parameters" IANA
   registries to identify MSD types as proposed in Section 3, Section 4.
   The registration procedure is "Expert Review" as defined in
   [RFC8126].  Suggested  The suggested registry name is "MSD types".  Types are an
   unsigned 8 bit number.  The following values are defined by this
   document
   document.

              Value     Name                             Reference
              -----     ---------------------            -------------
              0         Reserved                         This document
              1         Base MPLS Imposition MSD         This document
              2-250     Unassigned                       This document
              251-254   Experimental                     This document
              255       Reserved                         This document

                  Figure 3: MSD Types Codepoints Registry

8.  Security Considerations

   Security considerations, as specified by [RFC7770] are applicable to
   this document

9.  Contributors

   The following people contributed to this document:

   Les Ginsberg

   Email: ginsberg@cisco.com

10.  Acknowledgements

   The authors would like to thank Acee Lindem, Stephane Litkowski and
   Bruno Decraene for their reviews and valuable comments.

11.  References

11.1.  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,
              <https://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, <https://www.rfc-editor.org/info/rfc4970>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [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>.

11.2.  Informative References

   [I-D.ietf-idr-bgp-ls-segment-routing-msd]
              Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
              "Signaling Maximum SID Depth using Border Gateway Protocol
              Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01
              (work in progress), October 2017.

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

   [I-D.ietf-ospf-ospfv3-lsa-extend]
              Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.
              Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-
              lsa-extend-23 (work in progress), January 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-11 (work in progress),
              November 2017.

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

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Authors' Addresses

   Jeff Tantsura
   Nuage Networks

   Email: jefftant.ietf@gmail.com
   Uma Chunduri
   Huawei Technologies

   Email: uma.chunduri@huawei.com

   Sam Aldrin
   Google, Inc

   Email: aldrin.ietf@gmail.com

   Peter Psenak
   Cisco Systems

   Email: ppsenak@cisco.com