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Versions: (draft-ketant-idr-bgp-ls-flex-algo) 00 01

Inter-Domain Routing                                       K. Talaulikar
Internet-Draft                                                 P. Psenak
Intended status: Standards Track                           Cisco Systems
Expires: December 1, 2019                                       S. Zandi
                                                                G. Dawra
                                                                LinkedIn
                                                            May 30, 2019


    Flexible Algorithm Definition Advertisement with BGP Link-State
                   draft-ietf-idr-bgp-ls-flex-algo-00

Abstract

   Flexible Algorithm is a solution that allows routing protocols (viz.
   OSPF and IS-IS) to compute paths over a network based on user-defined
   (and hence, flexible) constraints and metrics.  The computation is
   performed by routers participating in the specific network in a
   distribute manner using a Flex Algorithm definition.  This definition
   provisioned on one or more routers and propagated (viz.  OSPF and IS-
   IS flooding) through the network.

   BGP Link-State (BGP-LS) enables the collection of various topology
   information from the network.  This draft defines extensions to BGP-
   LS address-family to advertise the Flexible Algorithm Definition as a
   part of the topology information from the network.

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

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any




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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 December 1, 2019.

Copyright Notice

   Copyright (c) 2019 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
   (https://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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  BGP-LS Extensions for Flex Algo Definition  . . . . . . . . .   4
     2.1.  Flex Algo Exclude Any Affinity  . . . . . . . . . . . . .   5
     2.2.  Flex Algo Include Any Affinity  . . . . . . . . . . . . .   6
     2.3.  Flex Algo Include All Affinity  . . . . . . . . . . . . .   7
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   4.  Manageability Considerations  . . . . . . . . . . . . . . . .   8
     4.1.  Operational Considerations  . . . . . . . . . . . . . . .   8
     4.2.  Management Considerations . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   IGP protocols (OSPF and IS-IS) traditionally compute best paths over
   the network based on the IGP metric assigned to the links.  Many
   network deployments use RSVP-TE [RFC3209] based or Segment Routing
   (SR) Policy [I-D.ietf-spring-segment-routing-policy] based solutions
   to enforce traffic over a path that is computed using different
   metrics or constraints than the shortest IGP path.
   [I-D.ietf-lsr-flex-algo] defines the Flexible Algorithm solution that




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   allows IGPs themselves to compute constraint based paths over the
   network.

   Flexible Algorithm is called so as it allows a user the flexibility
   to define

   o  the type of calculation to be used (e.g. shortest path)

   o  the metric type to be used (e.g.  IGP metric or TE metric)

   o  the set of constraints to be used (e.g. inclusion or exclusion of
      certain links using affinities)

   The operations of the flexible algorithm solution is described in
   detail in [I-D.ietf-lsr-flex-algo] and a high level summary of the
   same is described here for clarity.  The network operator enables the
   participation of specific nodes in the network for a specific
   algorithm and then provisions the definition of that flexible
   algorithm on one or more of these nodes.  The nodes where the
   flexible algorithm definition is advertised then flood these
   definitions via respective IGP (IS-IS and OSPFv2/v3) mechanisms to
   all other nodes in the network.  The nodes select the definition for
   each algorithm based on the flooded information in a deterministic
   manner and thus all nodes participating in a flexible algorithm
   computation arrive at a common understanding of the type of
   calculation that they need to use.

   When using Segment Routing (SR) [RFC8402] forwarding plane, the
   result of a flex algorithm computation is the provisioning of the
   Prefix SIDs associated with that algorithm with paths based on the
   topology computed based on that algorithm.  This flex algorithm
   computation is within an IGP area or level similar to the default
   shortest path tree (SPT) algorithm.

   The BGP-LS extensions for SR are defined in
   [I-D.ietf-idr-bgp-ls-segment-routing-ext] and includes the

   o  SR Algorithm TLV to indicate the participation of a node in a flex
      algorithm computation

   o  Prefix SID TLV to indicate the association of the Prefix-SIDs to a
      specific flex algorithm

   Thus a controller or a Path Computation Engine (PCE) is aware of the
   IGP topology across multiple domains which includes the above
   information related to the flexible algorithm.  This draft defines
   extensions to BGP-LS for carrying the Flexible Algorithm Definition
   information so that it enables the controller/PCE to learn the



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   mapping of the flex algorithm number to its definition in each area/
   domain of the underlying IGP.  The controller/PCE also learns the
   type of computation used and the constraints for the same.  This
   information can then be leveraged by it for setting up SR Policy
   paths end to end across domains by leveraging the appropriate Flex
   Algorithm specific Prefix SIDs in its Segment List
   [I-D.ietf-spring-segment-routing-policy]. e.g. picking the Flex
   Algorithm Prefix SID or ABRs/ASBRs corresponding to a definition that
   optimizes on the delay metric enables the PCE/controller to build an
   end to end low latency path across IGP domains with minimal Prefix-
   SIDs in the SID list.

2.  BGP-LS Extensions for Flex Algo Definition

   The BGP-LS [RFC7752] specifies the Node NLRI for advertisement of
   nodes and their attributes using the BGP-LS Attribute.  The Flexible
   Algorithm Definition (FAD) advertised by a node are considered as its
   node level attributes and advertised as such.

   This document defines a new BGP-LS Attribute TLV called the Flexible
   Algorithm Definition (FAD) TLV and its format is as follows:

      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            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Flex-Algorithm |   Metric-Type |   Calc-Type   |    Priority   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                sub-TLVs       ...                            //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 1: Flex Algorithm Definition TLV

     where:

   o  Type: TBD (see IANA Considerations Section 3)

   o  Length: variable.  Minimum of 8 octets.

   o  Flex-Algorithm : 1 octet value in the range between 128 and 255
      inclusive which is the range defined for Flexible Algorithms in
      the IANA "IGP Parameters" registries under the "IGP Algorithm
      Types" registry [I-D.ietf-lsr-flex-algo].

   o  Metric-Type : 1 octet value indicating the type of the metric used
      in the computation.  Values allowed come from the IANA "IGP




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      Parameters" registries under the "Flexible Algorithm Definition
      Metric-Type" registry [I-D.ietf-lsr-flex-algo].

   o  Calculation-Type : 1 octet value in the range between 0 and 127
      inclusive which is the range defined for the standard algorithms
      in the IANA "IGP Parameters" registries under the "IGP Algorithm
      Types" registry [I-D.ietf-lsr-flex-algo].

   o  Priority : 1 octet value between 0 and 255 inclusive that
      specifies the priority of the FAD.

   o  sub-TLVs : zero or more sub-TLVs may be included as described
      further in this section.

   The FAD TLV can only be added to the BGP-LS Attribute of the Node
   NLRI if the corresponding node originates the underlying IGP TLV/sub-
   TLV as described below.  This information is derived from the
   protocol specific advertisements as below..

   o  IS-IS, as defined by the ISIS Flexible Algorithm Definition sub-
      TLV in [I-D.ietf-lsr-flex-algo].

   o  OSPFv2/OSPFv3, as defined by the OSPF Flexible Algorithm
      Definition TLV in [I-D.ietf-lsr-flex-algo].

   The following sub-sections define the sub-TLVs for the FAD TLV.

2.1.  Flex Algo Exclude Any Affinity

   The Flex Algo Exclude Any Affinity sub-TLV is an optional sub-TLV
   that is used to carry the affinity constraints [RFC2702] associated
   with the flex algo definition and enable the exclusion of links
   carrying any of the specified affinities from the computation of the
   specific algorithm as described in [I-D.ietf-lsr-flex-algo].  The
   affinity is expressed in terms of Extended Admin Group (EAG) as
   defined in [RFC7308].

   The TLV has the following format:

    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           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Exclude-Any EAG (variable)                       //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:



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   o  Type: TBD (see IANA Considerations Section 3)

   o  Length: variable, dependent on the size of the Extended Admin
      Group.  MUST be a multiple of 4 octets.

   o  Exclude-Any EAG : the bitmask used to represent the affinities to
      be excluded.

   The information in the Flex Algo Exclude Any Affinity sub-TLV is
   derived from the IS-IS and OSPF protocol specific Flexible Algorithm
   Exclude Admin Group sub-TLV as defined in [I-D.ietf-lsr-flex-algo].

2.2.  Flex Algo Include Any Affinity

   The Flex Algo Incude Any Affinity sub-TLV is an optional sub-TLV that
   is used to carry the affinity constraints [RFC2702] associated with
   the flex algo definition and enable the inclusion of links carrying
   any of the specified affinities in the computation of the specific
   algorithm as described in [I-D.ietf-lsr-flex-algo].  The affinity is
   expressed in terms of Extended Admin Group (EAG) as defined in
   [RFC7308].

   The TLV has the following format:

    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           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Include-Any EAG (variable)                       //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o  Type: TBD (see IANA Considerations Section 3)

   o  Length: variable, dependent on the size of the Extended Admin
      Group.  MUST be a multiple of 4 octets.

   o  Include-Any EAG : the bitmask used to represent the affinities to
      be included.

   The information in the Flex Algo Include Any Affinity sub-TLV is
   derived from the IS-IS and OSPF protocol specific Flexible Algorithm
   Include-Any Admin Group sub-TLV as defined in
   [I-D.ietf-lsr-flex-algo].





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2.3.  Flex Algo Include All Affinity

   The Flex Algo Incude All Affinity sub-TLV is an optional sub-TLV that
   is used to carry the affinity constraints [RFC2702] associated with
   the flex algo definition and enable the inclusion of links carrying
   all of the specified affinities in the computation of the specific
   algorithm as described in [I-D.ietf-lsr-flex-algo].  The affinity is
   expressed in terms of Extended Admin Group (EAG) as defined in
   [RFC7308].

   The TLV has the following format:

    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           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Include-All EAG (variable)                       //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o  Type: TBD (see IANA Considerations Section 3)

   o  Length: variable, dependent on the size of the Extended Admin
      Group.  MUST be a multiple of 4 octets.

   o  Include-All EAG : the bitmask used to represent the affinities to
      be included.

   The information in the Flex Algo Include All Affinity sub-TLV is
   derived from the IS-IS and OSPF protocol specific Flexible Algorithm
   Include-All Admin Group sub-TLV as defined in
   [I-D.ietf-lsr-flex-algo].

3.  IANA Considerations

   This document requests assigning code-points from the registry "BGP-
   LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
   TLVs" based on table below.  The column "IS-IS TLV/Sub-TLV" defined
   in the registry does not require any value and should be left empty.










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    +------------+----------------------------------------+----------+
    | Code Point |         Description                    | Length   |
    +------------+----------------------------------------+----------+
    |    TBD     | Flex Algorithm Definition TLV          | variable |
    |    TBD     | Flex Algo Exclude Any Affinity sub-TLV | variable |
    |    TBD     | Flex Algo Include Any Affinity sub-TLV | variable |
    |    TBD     | Flex Algo Include All Affinity sub-TLV | variable |
    +------------+----------------------------------------+----------+


4.  Manageability Considerations

   This section is structured as recommended in [RFC5706].

   The new protocol extensions introduced in this document augment the
   existing IGP topology information that was distributed via [RFC7752].
   Procedures and protocol extensions defined in this document do not
   affect the BGP protocol operations and management other than as
   discussed in the Manageability Considerations section of [RFC7752].
   Specifically, the malformed NLRIs attribute tests in the Fault
   Management section of [RFC7752] now encompass the new TLVs for the
   BGP-LS NLRI in this document.

4.1.  Operational Considerations

   No additional operation considerations are defined in this document.

4.2.  Management Considerations

   No additional management considerations are defined in this document.

5.  Security Considerations

   The new protocol extensions introduced in this document augment the
   existing IGP topology information that was distributed via [RFC7752].
   Procedures and protocol extensions defined in this document do not
   affect the BGP security model other than as discussed in the Security
   Considerations section of [RFC7752].

6.  Acknowledgements

   The authors would like to thank Les Ginsberg for his reviews and
   contributions to this work.








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7.  References

7.1.  Normative References

   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
              algo-02 (work in progress), May 2019.

   [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>.

7.2.  Informative References

   [I-D.ietf-idr-bgp-ls-segment-routing-ext]
              Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
              and M. Chen, "BGP Link-State extensions for Segment
              Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-15
              (work in progress), May 2019.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
              bogdanov@google.com, b., and P. Mattes, "Segment Routing
              Policy Architecture", draft-ietf-spring-segment-routing-
              policy-03 (work in progress), May 2019.

   [RFC2702]  Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
              McManus, "Requirements for Traffic Engineering Over MPLS",
              RFC 2702, DOI 10.17487/RFC2702, September 1999,
              <https://www.rfc-editor.org/info/rfc2702>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.




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   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions",
              RFC 5706, DOI 10.17487/RFC5706, November 2009,
              <https://www.rfc-editor.org/info/rfc5706>.

   [RFC7308]  Osborne, E., "Extended Administrative Groups in MPLS
              Traffic Engineering (MPLS-TE)", RFC 7308,
              DOI 10.17487/RFC7308, July 2014,
              <https://www.rfc-editor.org/info/rfc7308>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

Authors' Addresses

   Ketan Talaulikar
   Cisco Systems
   India

   Email: ketant@cisco.com


   Peter Psenak
   Cisco Systems
   Slovakia

   Email: ppsenak@cisco.com


   Shawn Zandi
   LinkedIn
   USA

   Email: szandi@linkedin.com


   Gaurav Dawra
   LinkedIn
   USA

   Email: gdawra.ietf@gmail.com








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