



Inter-Domain Routing                                  K. Talaulikar, Ed.
Internet-Draft                                               Arrcus, Inc
Intended status: Standards Track                               P. Psenak
Expires: 26 February 2023                                  Cisco Systems
                                                                S. Zandi
                                                                G. Dawra
                                                                LinkedIn
                                                          25 August 2022


         Flexible Algorithm Advertisement using BGP Link-State
                   draft-ietf-idr-bgp-ls-flex-algo-12

Abstract

   Flexible Algorithm is a solution that allows some routing protocols
   (e.g., 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 distributed manner using a Flexible Algorithm
   Definition.  This Definition is provisioned on one or more routers
   and propagated through the network by OSPF and IS-IS flooding.

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

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
   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 26 February 2023.







Talaulikar, et al.      Expires 26 February 2023                [Page 1]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


Copyright Notice

   Copyright (c) 2022 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Overview of BGP-LS Extensions for Flexible Algorithm  . . . .   4
   3.  Flexible Algorithm Definition TLV . . . . . . . . . . . . . .   4
     3.1.  Flexible Algorithm Exclude Any Affinity Sub-TLV . . . . .   6
     3.2.  Flexible Algorithm Include Any Affinity Sub-TLV . . . . .   6
     3.3.  Flexible Algorithm Include All Affinity Sub-TLV . . . . .   7
     3.4.  Flexible Algorithm Definition Flags Sub-TLV . . . . . . .   8
     3.5.  Flexible Algorithm Exclude SRLG Sub-TLV . . . . . . . . .   9
     3.6.  Flexible Algorithm Unsupported Sub-TLV  . . . . . . . . .  10
   4.  Flexible Algorithm Prefix Metric TLV  . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   6.  Manageability Considerations  . . . . . . . . . . . . . . . .  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   The classical IGP (e.g., OSPF and IS-IS) computation of best paths
   over the network is based on the IGP metric assigned to the links in
   the network.  Many network deployments use RSVP-TE-based [RFC3209] or
   Segment Routing (SR) Policy-based [RFC8402] 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 allows IGPs themselves
   to compute constraint based paths over the network.





Talaulikar, et al.      Expires 26 February 2023                [Page 2]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


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

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

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

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

   The operations of the IGP flexible algorithm solution are described
   in detail in [I-D.ietf-lsr-flex-algo].

   The BGP-LS extensions for SR are defined in [RFC9085] and
   [I-D.ietf-idr-bgpls-srv6-ext] for SR-MPLS and Segment Routing over
   IPv6 (SRv6), respectively.  They include the extensions for
   advertisement of SR information including various types of Segment
   Identifiers (SIDs) as below:

   *  SR Algorithm TLV to indicate the participation of a node in a
      flexible algorithm computation

   *  Prefix-SID TLV to indicate the association of the Prefix-SIDs to a
      specific flexible algorithm for SR-MPLS forwarding

   *  SRv6 Locator TLV to indicate the Locator for specific flexible
      algorithm for SRv6 forwarding

   This document defines extensions to BGP-LS for the advertisement of
   the Flexible Algorithm Definition (FAD) information to enable
   learning of the mapping of the flexible algorithm number to its
   Definition in each area/domain of the underlying IGP.  This
   Definition indicates the type of computation used and the constraints
   for a given flexible algorithm.  This information can then be used
   for setting up SR Policy paths end to end across domains by using the
   appropriate flexible algorithm-specific SIDs in its Segment List
   [RFC9256].  For example, picking the flexible algorithm Prefix SID
   (in case of SR-MPLS) or End SID (in case of SRv6) of Area Border
   Routers (ABRs) or Autonomous System Border Routers (ASBRs)
   corresponding to a Definition that optimizes on the delay metric
   enables the building of an end to end low latency path across IGP
   domains with minimal SIDs in the SID list.









Talaulikar, et al.      Expires 26 February 2023                [Page 3]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


1.1.  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.

2.  Overview of BGP-LS Extensions for Flexible Algorithm

   BGP-LS [RFC7752] specifies the Node Network Layer Reachability
   Information (NLRI) for the advertisement of nodes along with their
   attributes using the BGP-LS Attribute, the Link NLRI for the
   advertisement of links along with their attributes using the BGP-LS
   Attribute and the Prefix NLRI for the advertisement of prefixes along
   with their attributes using the BGP-LS Attribute.

   The FADs advertised by a node are considered as a node-level
   attribute and advertised as specified in Section 3.

   Various link attributes like affinities and Shared Risk Link Group
   (SRLG) that are used during the Flexible Algorithm route calculations
   in IS-IS and OSPF are advertised in those protocols using the
   Application Specific Link Attribute (ASLA) advertisements as
   described in [RFC8919], [RFC8920], and [I-D.ietf-lsr-flex-algo].  The
   BGP-LS extensions for ASLA advertisements are specified in [RFC9294].

   The Flexible Algorithm Prefix Metric (FAPM) is considered as a prefix
   attribute and advertised as specified in Section 4.

3.  Flexible Algorithm Definition TLV

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
















Talaulikar, et al.      Expires 26 February 2023                [Page 4]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


      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 Algo   |   Metric-Type |   Calc-Type   |    Priority   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                sub-TLVs       ...                            //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 1: Flexible Algorithm Definition TLV

     where:

   *  Type: 1039

   *  Length: The total length of the value field (including any sub-
      TLVs) in octets.  The length value MUST be 4 or larger.

   *  Flexible Algorithm (Flex Algo): Single octet value carrying the
      flexible algorithm number between 128 and 255 inclusive, as
      defined in [I-D.ietf-lsr-flex-algo].

   *  Metric-Type: Single octet value carrying the metric type, as
      defined in [I-D.ietf-lsr-flex-algo].

   *  Calc-Type: Single octet value carrying the calculation type, as
      defined in [I-D.ietf-lsr-flex-algo].

   *  Priority: Single octet value carrying the priority of the FAD
      advertisement, as defined in [I-D.ietf-lsr-flex-algo].

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

   The FAD TLV that is advertised in the BGP-LS Attribute along with the
   Node NLRI of a node is derived from the following IGP protocol-
   specific advertisements:

   *  In the case of IS-IS, from the IS-IS Flexible Algorithm Definition
      sub-TLV in [I-D.ietf-lsr-flex-algo].

   *  In the case of OSPFv2/OSPFv3, from the OSPF Flexible Algorithm
      Definition TLV in [I-D.ietf-lsr-flex-algo].

   The BGP-LS Attribute associated with a Node NLRI may include one or
   more FAD TLVs corresponding to the FAD for each algorithm that the
   particular node is advertising.



Talaulikar, et al.      Expires 26 February 2023                [Page 5]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


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

3.1.  Flexible Algorithm Exclude Any Affinity Sub-TLV

   The Flexible Algorithm Exclude Any Affinity sub-TLV is an optional
   sub-TLV that is used to carry the affinity constraints associated
   with the FAD 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 sub-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)                       //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 2: Flexible Algorithm Exclude Any Affinity sub-TLV

   where:

   *  Type: 1040

   *  Length: The total length of the value field in octets dependent on
      the size of the EAG.  It MUST be a non-zero value and a multiple
      of 4.

   *  Exclude-Any EAG: the EAG value as defined in
      [I-D.ietf-lsr-flex-algo].

   The information in the Flexible Algorithm 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].

3.2.  Flexible Algorithm Include Any Affinity Sub-TLV

   The Flexible Algorithm Include Any Affinity sub-TLV is an optional
   sub-TLV that is used to carry the affinity constraints associated
   with the FAD 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].




Talaulikar, et al.      Expires 26 February 2023                [Page 6]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


   The sub-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)                       //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 3: Flexible Algorithm Include Any Affinity sub-TLV

   where:

   *  Type: 1041

   *  Length: The total length of the value field in octets dependent on
      the size of the EAG.  It MUST be a non-zero value and a multiple
      of 4.

   *  Include-Any EAG: the EAG value as defined in
      [I-D.ietf-lsr-flex-algo].

   The information in the Flexible Algorithm 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].

3.3.  Flexible Algorithm Include All Affinity Sub-TLV

   The Flexible Algorithm Include All Affinity sub-TLV is an optional
   sub-TLV that is used to carry the affinity constraints associated
   with the FAD 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 sub-TLV has the following format:













Talaulikar, et al.      Expires 26 February 2023                [Page 7]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


    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)                       //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 4: Flexible Algorithm Include All Affinity sub-TLV

   where:

   *  Type: 1042

   *  Length: The total length of the value field in octets dependent on
      the size of the EAG.  It MUST be a non-zero value and a multiple
      of 4.

   *  Include-All EAG: the EAG value as defined in
      [I-D.ietf-lsr-flex-algo].

   The information in the Flexible Algorithm 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].

3.4.  Flexible Algorithm Definition Flags Sub-TLV

   The Flexible Algorithm Definition Flags sub-TLV is an optional sub-
   TLV that is used to carry the flags associated with the FAD that are
   used in the computation of the specific algorithm as described in
   [I-D.ietf-lsr-flex-algo].

   The sub-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           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Flags (variable)                       //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 5: Flexible Algorithm Definition Flags sub-TLV

   where:

   *  Type: 1043



Talaulikar, et al.      Expires 26 February 2023                [Page 8]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


   *  Length: The total length of the value field in octets dependent on
      the size of the Flags.  It MUST be a non-zero value and a multiple
      of 4.

   *  Flags: the bitmask used to represent the flags for the FAD, as
      defined in [I-D.ietf-lsr-flex-algo].

   The information in the Flexible Algorithm Definition Flags sub-TLV is
   derived from the IS-IS and OSPF protocol-specific Flexible Algorithm
   Definition Flags sub-TLV as defined in [I-D.ietf-lsr-flex-algo].

3.5.  Flexible Algorithm Exclude SRLG Sub-TLV

   The Flexible Algorithm Exclude SRLG sub-TLV is an optional sub-TLV
   that is used to carry the Shared Risk Link Group (SRLG) information
   associated with the FAD and enable the exclusion of links that are
   associated with any of the specified SRLG in the computation of the
   specific algorithm as described in [I-D.ietf-lsr-flex-algo].  The
   SRLGs associated with a link are carried in the BGP-LS Shared Link
   Risk Group (TLV 1096) [RFC7752].

   The sub-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           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Shared Risk Link Group Values (variable)           //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 6: Flexible Algorithm Exclude SRLG sub-TLV

   where:

   *  Type: 1045

   *  Length: The total length of the value field in octets dependent on
      the number of SRLG values carried.  It MUST be a non-zero value
      and a multiple of 4.

   *  Shared Risk Link Group Values: One or more SRLG values, each of 4
      octet size, as defined in [I-D.ietf-lsr-flex-algo].

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




Talaulikar, et al.      Expires 26 February 2023                [Page 9]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


3.6.  Flexible Algorithm Unsupported Sub-TLV

   The OSPF and IS-IS signaling for FAD allows for extensions via new
   sub-TLVs under the respective IGP's Flexible Algorithm Definition
   TLV.  As specified in section 5.3 of [I-D.ietf-lsr-flex-algo], it is
   important that the entire FAD be understood by anyone using it for
   computation purpose.  Therefore, the FAD is different from most other
   protocol extensions where the skipping or ignoring of unsupported
   sub-TLV information does not affect the base behavior.

   The Flexible Algorithm Unsupported sub-TLV is an optional sub-TLV
   that is used to indicate the presence of unsupported FAD sub-TLVs.
   The need for this sub-TLV arises when the BGP-LS implementation on
   the advertising node does not support one or more of the FAD sub-TLVs
   present in the IGP advertisement.

   The sub-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           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Protocol-ID  | sub-TLV types (variable) ...                 //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 7: Flexible Algorithm Unsupported sub-TLV

   where:

   *  Type: TBD (Note to Editor: The code point allocation, once made by
      IANA, needs to be updated here - refer to Section 5)

   *  Length: The total length of the value field in octets (including
      any included sub-TLV types).

   *  Protocol-ID: Indicates the BGP-LS Protocol-ID of the protocol from
      which the FAD is being advertised via BGP-LS.  The values are from
      the "BGP-LS Protocol-IDs" registry
      <https://www.iana.org/assignments/bgp-ls-parameters/bgp-ls-
      parameters.xhtml#protocol-ids> under the IANA BGP-LS Parameters
      registry.









Talaulikar, et al.      Expires 26 February 2023               [Page 10]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


   *  sub-TLV types: Zero or more sub-TLV types that are not supported
      by the node originating the BGP-LS advertisement.  The size of
      each sub-TLV type depends on the protocol indicated by the
      Protocol-ID field.  For example, for IS-IS each sub-TLV type would
      be of size 1 octet while for OSPF each sub-TLV type would be of
      size 2 octets.

   The node originating the advertisement MUST include the Flexible
   Algorithm Unsupported sub-TLV when it comes across an unsupported
   sub-TLV in the corresponding FAD in the IS-IS and OSPF advertisement.
   When advertising the Flexible Algorithm Unsupported sub-TLV, the
   protocol-specific sub-TLV types that are not supported SHOULD be
   included.  This information serves as a diagnostic aid.

   The discussion on the use of the FAD information by the consumers of
   the BGP-LS information is beyond the scope of this document.
   However, it is RECOMMENDED that the choice of the node used for
   originating the IGP topology information into BGP-LS be made such
   that the advertising node supports all the FAD extensions in use in
   its part of the network.  This avoids the scenario where an
   incomplete FAD gets advertised via BGP-LS.

4.  Flexible Algorithm Prefix Metric TLV

   This document defines a new optional BGP-LS Attribute TLV associated
   with the Prefix NLRI called the Flexible Algorithm Prefix Metric
   (FAPM) 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 Algo   |     Flags     |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Metric                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 8: Flexible Algorithm Prefix Metric TLV

   where:

   *  Type: 1044

   *  Length: 8 octets.






Talaulikar, et al.      Expires 26 February 2023               [Page 11]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


   *  Flexible Algorithm (Flex Algo): Single octet value carrying the
      flexible algorithm number between 128 and 255 inclusive, as
      defined in [I-D.ietf-lsr-flex-algo].

   *  Flags: single octet value and only applicable for OSPF as defined
      in [I-D.ietf-lsr-flex-algo].  The value MUST be set to 0 for IS-
      IS.

   *  Reserved: 2 octet value that MUST be set to 0 by the originator
      and MUST be ignored by the receiver.

   *  Metric: 4 octets field to carry the metric information.

   The FAPM TLV that is advertised in the BGP-LS Attribute along with
   the Prefix NLRI from a node is derived from the following IGP
   protocol-specific advertisements:

   *  In the case of IS-IS, from the IS-IS Flexible Algorithm Prefix
      Metric sub-TLV in [I-D.ietf-lsr-flex-algo].

   *  In the case of OSPFv2/OSPFv3, from the OSPF Flexible Algorithm
      Prefix Metric sub-TLV in [I-D.ietf-lsr-flex-algo].

   The BGP-LS Attribute associated with a Prefix NLRI may include one or
   more FAPM TLVs corresponding to the Flexible Algorithm Prefix Metric
   for each algorithm associated with that particular prefix.

5.  IANA Considerations

   IANA has allocated code points from the registry "BGP-LS Node
   Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs"
   <https://www.iana.org/assignments/bgp-ls-parameters/bgp-ls-
   parameters.xhtml#node-descriptor-link-descriptor-prefix-descriptor-
   attribute-tlv> based on the table below for the TLVs/sub-TLVs
   introduced by this document.  This document requests IANA to allocate
   the pending code point for the Flexible Algorithm Unsupported sub-TLV
   as suggested below.  The column "IS-IS TLV/Sub-TLV" defined in the
   registry does not require any value and should be left empty.













Talaulikar, et al.      Expires 26 February 2023               [Page 12]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


         +------------+-----------------------------------------+
         | Code Point |         Description                     |
         +------------+-----------------------------------------+
         | 1039       | Flexible Algorithm Definition           |
         | 1040       | Flexible Algorithm Exclude Any Affinity |
         | 1041       | Flexible Algorithm Include Any Affinity |
         | 1042       | Flexible Algorithm Include All Affinity |
         | 1043       | Flexible Algorithm Definition Flags     |
         | 1044       | Flexible Algorithm Prefix Metric        |
         | 1045       | Flexible Algorithm Exclude SRLG         |
         | 1046 (Sugg)| Flexible Algorithm Unsupported          |
         +------------+-----------------------------------------+

             Table 1: Flexible Algorithm Code Points

6.  Manageability Considerations

   The new protocol extensions introduced in this document augment the
   existing IGP topology information that can be 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.

   The extensions specified in this document do not specify any new
   configuration or monitoring aspects in BGP or BGP-LS.  The
   specification of BGP models is an ongoing work based on
   [I-D.ietf-idr-bgp-model].

7.  Security Considerations

   Security considerations for acquiring and distributing BGP-LS
   information are discussed in [RFC7752].

   The TLVs introduced in this document are used to propagate the IGP
   Flexible Algorithm extensions defined in [I-D.ietf-lsr-flex-algo].
   It is assumed that the IGP instances originating these TLVs will
   support all the required security (as described in
   [I-D.ietf-lsr-flex-algo]) for Flexible Algorithm deployment.










Talaulikar, et al.      Expires 26 February 2023               [Page 13]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


   This document specifies extensions for the advertisement of node and
   prefix related flexible algorithm information.  Tampering with this
   flexible algorithm-related information may affect applications using
   it, including impacting route calculation and programming.  As the
   advertisements defined in this document are related to a specific
   flexible algorithm topology, the impact of tampering is similarly
   limited in scope.

8.  Acknowledgements

   The authors would like to thank Les Ginsberg, Amalesh Maity, Y F Siu,
   Vijay Gurbani, and Donald Eastlake III for their reviews and
   contributions to this work.  The authors would like to thank Jie Dong
   for his shepherd review.  The authors would like to thank Alvaro
   Retana for his detailed AD review and suggestions for improving this
   document.

9.  References

9.1.  Normative References

   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", Work in Progress,
              Internet-Draft, draft-ietf-lsr-flex-algo-20, 18 May 2022,
              <https://www.ietf.org/archive/id/draft-ietf-lsr-flex-algo-
              20.txt>.

   [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>.

   [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>.

   [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>.




Talaulikar, et al.      Expires 26 February 2023               [Page 14]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


9.2.  Informative References

   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
              YANG Model for Service Provider Networks", Work in
              Progress, Internet-Draft, draft-ietf-idr-bgp-model-14, 3
              July 2022, <https://www.ietf.org/archive/id/draft-ietf-
              idr-bgp-model-14.txt>.

   [I-D.ietf-idr-bgpls-srv6-ext]
              Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
              Bernier, D., and B. Decraene, "BGP Link State Extensions
              for SRv6", Work in Progress, Internet-Draft, draft-ietf-
              idr-bgpls-srv6-ext-09, 10 November 2021,
              <https://www.ietf.org/archive/id/draft-ietf-idr-bgpls-
              srv6-ext-09.txt>.

   [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>.

   [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>.

   [RFC8919]  Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
              J. Drake, "IS-IS Application-Specific Link Attributes",
              RFC 8919, DOI 10.17487/RFC8919, October 2020,
              <https://www.rfc-editor.org/info/rfc8919>.

   [RFC8920]  Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
              J., and J. Drake, "OSPF Application-Specific Link
              Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020,
              <https://www.rfc-editor.org/info/rfc8920>.

   [RFC9085]  Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
              H., and M. Chen, "Border Gateway Protocol - Link State
              (BGP-LS) Extensions for Segment Routing", RFC 9085,
              DOI 10.17487/RFC9085, August 2021,
              <https://www.rfc-editor.org/info/rfc9085>.

   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
              A., and P. Mattes, "Segment Routing Policy Architecture",
              RFC 9256, DOI 10.17487/RFC9256, July 2022,
              <https://www.rfc-editor.org/info/rfc9256>.




Talaulikar, et al.      Expires 26 February 2023               [Page 15]

Internet-Draft  BGP-LS Extensions for Flexible Algorithm     August 2022


   [RFC9294]  Talaulikar, K., Ed., Psenak, P., and J. Tantsura,
              "Application-Specific Link Attributes Advertisement Using
              the Border Gateway Protocol - Link State (BGP-LS)",
              RFC 9294, DOI 10.17487/RFC9294, August 2022,
              <https://www.rfc-editor.org/info/rfc9294>.

Authors' Addresses

   Ketan Talaulikar (editor)
   Arrcus, Inc
   India
   Email: ketant.ietf@gmail.com


   Peter Psenak
   Cisco Systems
   Slovakia
   Email: ppsenak@cisco.com


   Shawn Zandi
   LinkedIn
   United States of America
   Email: szandi@linkedin.com


   Gaurav Dawra
   LinkedIn
   United States of America
   Email: gdawra.ietf@gmail.com





















Talaulikar, et al.      Expires 26 February 2023               [Page 16]
