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IGP Flexible Algorithms Reverse Affinity Constraint
draft-ietf-lsr-igp-flex-algo-reverse-affinity-04

Document Type Active Internet-Draft (lsr WG)
Authors Peter Psenak , Jakub Horn , Amit Dhamija
Last updated 2025-02-13 (Latest revision 2025-01-28)
Replaces draft-ppsenak-lsr-igp-flex-algo-reverse-affinity
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draft-ietf-lsr-igp-flex-algo-reverse-affinity-04
LSR Working Group                                              P. Psenak
Internet-Draft                                                   J. Horn
Intended status: Standards Track                           Cisco Systems
Expires: 1 August 2025                                        A. Dhamija
                                                                  Arrcus
                                                         28 January 2025

          IGP Flexible Algorithms Reverse Affinity Constraint
            draft-ietf-lsr-igp-flex-algo-reverse-affinity-04

Abstract

   An IGP Flexible Algorithm (Flex-Algorithm) allows IGPs to compute
   constraint-based paths.

   This document extends IGP Flex-Algorithm with additional constraints
   for inclusion or exclusion of links in the path based on Admin Groups
   associated with the reverse direction of the SPF path computation.

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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   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 1 August 2025.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Use Case Example  . . . . . . . . . . . . . . . . . . . . . .   3
   4.  IS-IS Flexible Algorithm Exclude Reverse Admin Group
           Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  IS-IS Flexible Algorithm Include-Any Reverse Admin Group
           Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  IS-IS Flexible Algorithm Include-All Reverse Admin Group
           Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  OSPF Flexible Algorithm Exclude Reverse Admin Group
           Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  OSPF Flexible Algorithm Include-Any Reverse Admin Group
           Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  OSPF Flexible Algorithm Include-All Reverse Admin Group
           Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . .   6
   10. Calculation of Flexible Algorithm Paths . . . . . . . . . . .   7
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  Sub-Sub-TLVs for Flexible Algorithm Definition
            Sub-TLV  . . . . . . . . . . . . . . . . . . . . . . . .   7
     11.2.  OSPF Flexible Algorithm Definition TLV Sub-TLV
            Registry . . . . . . . . . . . . . . . . . . . . . . . .   8
     11.3.  IGP Flex-Algo Path Computation Rules Registry  . . . . .   8
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   14. Normative References  . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   An IGP Flex-Algorithm as specified in [RFC9350] computes a
   constraint-based path.

   This document extends IGP Flex-Algorithm with additional constraints
   for inclusion or exclusion of links in the path based on Admin Groups
   associated with the reverse direction of the SPF path computation.

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

3.  Use Case Example

   The Flexible Algorithm definition can specify Admin Groups that are
   used by the operator to include or exclude links during the Flex-
   Algorithm path computation.  These link Admin Groups are checked in
   the path direction of the SPF computation, e.g., in the direction
   from the root vertex toward verticies of increasing distance.

   In some cases, it is beneficial to check the Admin Groups of the link
   from the reverse direction of the path computation.  For example, on
   a point-to-point link between endpoints A and B and for the path
   copmputed in a direction from A to B, the input errors can only be
   detected at node B.  An operator may measure the rate of such input
   errors and set certain Admin Groups on a link locally on node B when
   the input error rate exceeds a certain threshold.  When the Flex-
   Algorithm calculation processes the link A to B, it may look at the
   Admin Groups of link's reverse direction, e.g., from B to A.  This
   would allow the operator to exclude such link from the Flex-Algorithm
   topology.

4.  IS-IS Flexible Algorithm Exclude Reverse Admin Group Sub-TLV

   The IS-IS Flexible Algorithm Exclude Reverse Admin Group (FAERAG)
   Sub-TLV is used to advertise the exclude rule that is used during the
   Flex-Algorithm path calculation as specified in Section 10.

   The IS-IS FAERAG Sub-TLV is a Sub-TLV of the IS-IS FAD Sub-TLV.  It
   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     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Extended Admin Group                     |
   +-                                                             -+
   |                            ...                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   where:

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      Type (1 octet): An 8-bit field assigned by IANA to uniquely
      identify the ISIS FAERAG Sub-TLV.  Value 10 has been assigned by
      IANA.

      Length (1 octet): Variable, dependent on the size of the Extended
      Admin Group.  The length MUST be a multiple of 4 octets.  If the
      length is not a multiple of 4 octets, the entire Sub-TLV MUST be
      ignored by the receiver.

      Extended Administrative Group: Extended Administrative Group as
      defined in [RFC7308].

   The IS-IS FAERAG Sub-TLV MUST NOT appear more than once in a single
   IS-IS FAD Sub-TLV.  If it appears more than once, the IS-IS FAD Sub-
   TLV MUST be ignored by the receiver.

   The IS-IS FAERAG Sub-TLV MUST NOT appear more than once in the set of
   FAD sub-TLVs for a given Flex-Algorithm from a given IS.  If it
   appears more than once in such set, the IS-IS FAERAG Sub-TLV in the
   first occurrence in the lowest numbered LSP from a given IS MUST be
   used and any other occurrences MUST be ignored by the receiver.

5.  IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV

   The IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV
   is used to advertise the include-any rule that is used during the
   Flex-Algorithm path calculation as specified in Section 10.

   The format of the IS-IS Flexible Algorithm Include-Any Reverse Admin
   Group Sub-TLV is identical to the format of the FAERAG Sub-TLV in
   Section 4.

   IANA has assigned Type value of 11 for the IS-IS Flexible Algorithm
   Include-Any Reverse Admin Group Sub-TLV.

   The IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV
   MUST NOT appear more than once in a single IS-IS FAD Sub-TLV.  If it
   appears more than once, the IS-IS FAD Sub-TLV MUST be ignored by the
   receiver.

   The IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV
   MUST NOT appear more than once in the set of FAD sub-TLVs for a given
   Flex-Algorithm from a given IS.  If it appears more than once in such
   set, the IS-IS Flexible Algorithm Include-Any Reverse Admin Group
   Sub-TLV in the first occurrence in the lowest numbered LSP from a
   given IS MUST be used and any other occurrences MUST be ignored by
   the receiver.

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6.  IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV

   The IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV
   is used to advertise the include-all rule that is used during the
   Flex-Algorithm path calculation as specified in Section 10.

   The format of the IS-IS Flexible Algorithm Include-All Reverse Admin
   Group Sub-TLV is identical to the format of the FAERAG Sub-TLV in
   Section 4.

   IANA has assigned Type value of 12 for the IS-IS Flexible Algorithm
   Include-All Reverse Admin Group Sub-TLV.

   The IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV
   MUST NOT appear more than once in a single IS-IS FAD Sub-TLV.  If it
   appears more than once, the IS-IS FAD Sub-TLV MUST be ignored by the
   receiver.

   The IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV
   MUST NOT appear more than once in the set of FAD sub-TLVs for a given
   Flex-Algorithm from a given IS.  If it appears more than once in such
   set, the IS-IS Flexible Algorithm Include-All Reverse Admin Group
   Sub-TLV in the first occurrence in the lowest numbered LSP from a
   given IS MUST be used and any other occurrences MUST be ignored by
   the receiver.

7.  OSPF Flexible Algorithm Exclude Reverse Admin Group Sub-TLV

   The OSPF Flexible Algorithm Exclude Reverse Admin Group (FAERAG) Sub-
   TLV is used to advertise the exclude rule that is used during the
   Flex-Algorithm path calculation as specified in Section 10.

   The OSPF FAERAG Sub-TLV is a Sub-TLV of the OSPF FAD TLV.  It 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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Extended Admin Group                     |
   +-                                                             -+
   |                            ...                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   where:

      Type (2 octets): A 16-bit field assigned by IANA to uniquely

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      identify the OSPF FAERAG Sub-TLV.  Value 10 has been assigned by
      IANA.

      Length (2 octets): Variable, dependent on the size of the Extended
      Admin Group.  The length MUST be a multiple of 4 octets.  If the
      length is not a multiple of 4 octets, the entire Sub-TLV MUST be
      ignored by the receiver.

      Extended Administrative Group: Extended Administrative Group as
      defined in [RFC7308].

   The OSPF FAERAG Sub-TLV MUST NOT appear more than once in an OSPF FAD
   TLV.  If it appears more than once, the OSPF FAD TLV MUST be ignored
   by the receiver.

8.  OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV

   The OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV
   is used to advertise the include-any rule that is used during the
   Flex-Algorithm path calculation as specified in Section 10.

   The format of the OSPF Flexible Algorithm Include-Any Reverse Admin
   Group Sub-TLV is identical to the format of the OSPF FAERAG Sub-TLV
   in Section 7.

   IANA has assigned Type value of 11 for the OSPF Flexible Algorithm
   Include-Any Reverse Admin Group Sub-TLV.

   The OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV
   MUST NOT appear more than once in an OSPF FAD TLV.  If it appears
   more than once, the OSPF FAD TLV MUST be ignored by the receiver.

9.  OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLV

   The OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLV
   is used to advertise the include-all rule that is used during the
   Flex-Algorithm path calculation as specified in Section 10.

   The format of the OSPF Flexible Algorithm Include-All Reverse Admin
   Group Sub-TLV is identical to the format of the OSPF FAERAG Sub-TLV
   in Section 7.

   IANA has assigned Type value of 12 for OSPF Flexible Algorithm
   Include-All Reverse Admin Group Sub-TLV.

   The OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLV
   MUST NOT appear more than once in an OSPF FAD TLV.  If it appears
   more than once, the OSPF FAD TLV MUST be ignored by the receiver.

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10.  Calculation of Flexible Algorithm Paths

   Three new rules are added to the existing rules specified in
   Section 13 of [RFC9350]:

      Check if any exclude reverse Admin Group rule is part of the Flex-
      Algorithm definition.  If such exclude rule exists, check if any
      Admin Group that is part of the exclude rule is also set on the
      link in the reverse direction.  If such Admin Group is set on the
      link in the reverse direction, the link MUST be pruned from the
      computation.

      Check if any include-any reverse Admin Group rule is part of the
      Flex-Algorithm definition.  If such include-any rule exists, check
      if any Admin Group that is part of the include-any rule is also
      set on the link in the reverse direction.  If no such Admin Group
      is set on the link in the reverse direction, the link MUST be
      pruned from the computation.

      Check if any include-all reverse Admin Group rule is part of the
      Flex-Algorithm definition.  If such include-all rule exists, check
      if all Admin Groups that are part of the include-all rule are also
      set on the link in the reverse direction.  If all such Admin
      Groups are not set on the link in the reverse direction, the link
      MUST be pruned from the computation.

   Please see rules 8, 9, and 10 in Section 11.3 for these added rules.

11.  IANA Considerations

11.1.  Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV

   IANA has assigned the following Sub-Sub-TLVs in the "ISIS Sub-Sub-
   TLVs for Flexible Algorithm Definition Sub-TLV" registry:

      Type: 10

      Description: Flexible Algorithm Exclude Reverse Admin Group

      Reference: This document (Section 4).

      Type: 11

      Description: Flexible Algorithm Include-Any Reverse Admin Group

      Reference: This document (Section 5).

      Type: 12

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      Description: Flexible Algorithm Include-All Reverse Admin Group

      Reference: This document (Section 6).

11.2.  OSPF Flexible Algorithm Definition TLV Sub-TLV Registry

   IANA has assigned the following Sub-TLVs in the "OSPF TLVs for
   Flexible Algorithm Definition TLV" registry:

      Type: 10

      Description: Flexible Algorithm Exclude Reverse Admin Group

      Reference: This document (Section 7).

      Type: 11

      Description: Flexible Algorithm Include-Any Reverse Admin Group

      Reference: This document (Section 8).

      Type: 12

      Description: Flexible Algorithm Include-All ReverseAdmin Group

      Reference: This document (Section 9).

11.3.  IGP Flex-Algo Path Computation Rules Registry

   This document creates a new registry called "IGP Flex-Algorithm Path
   Computation Rules Registry" within the "Interior Gateway Protocol
   (IGP) Parameters" registry group.  The registration procedure for the
   new registry is "Expert Review".

   The "IGP Flex-Algo Path Computation Rules Registry" specifies the
   ordered set of rules that MUST be used to prune links from the
   topology during the Flex-Algorithm path computation.

   +========+========================+=================================+
   | Number | Description            | Reference                       |
   +========+========================+=================================+
   | 1      | Check if any exclude   | Section 13 of [RFC9350]         |
   |        | Administrative Group   |                                 |
   |        | rule is part of the    |                                 |
   |        | Flex-Algorithm         |                                 |
   |        | Definition.  If such   |                                 |
   |        | exclude rule exists,   |                                 |
   |        | check if any color     |                                 |

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   |        | that is part of the    |                                 |
   |        | exclude rule is also   |                                 |
   |        | set on the link.  If   |                                 |
   |        | such a color is set,   |                                 |
   |        | the link MUST be       |                                 |
   |        | pruned from the        |                                 |
   |        | computation            |                                 |
   +--------+------------------------+---------------------------------+
   | 2      | Check if any exclude   | Section 13 of [RFC9350]         |
   |        | SRLG rule is part of   |                                 |
   |        | the Flex-Algorithm     |                                 |
   |        | Definition.  If such   |                                 |
   |        | exclude rule exists,   |                                 |
   |        | check if the link is   |                                 |
   |        | part of any SRLG that  |                                 |
   |        | is also part of the    |                                 |
   |        | SRLG exclude rule.     |                                 |
   |        | If the link is part    |                                 |
   |        | of such SRLG, the      |                                 |
   |        | link MUST be pruned    |                                 |
   |        | from the computation.  |                                 |
   +--------+------------------------+---------------------------------+
   | 3      | Check if any include-  | Section 13 of [RFC9350]         |
   |        | any Administrative     |                                 |
   |        | Group rule is part of  |                                 |
   |        | the Flex-Algorithm     |                                 |
   |        | Definition.  If such   |                                 |
   |        | include-any rule       |                                 |
   |        | exists, check if any   |                                 |
   |        | color that is part of  |                                 |
   |        | the include-any rule   |                                 |
   |        | is also set on the     |                                 |
   |        | link.  If no such      |                                 |
   |        | color is set, the      |                                 |
   |        | link MUST be pruned    |                                 |
   |        | from the computation   |                                 |
   +--------+------------------------+---------------------------------+
   | 4      | Check if any include-  | Section 13 of [RFC9350]         |
   |        | all Administrative     |                                 |
   |        | Group rule is part of  |                                 |
   |        | the Flex-Algorithm     |                                 |
   |        | Definition.  If such   |                                 |
   |        | include-all rule       |                                 |
   |        | exists, check if all   |                                 |
   |        | colors that are part   |                                 |
   |        | of the include-all     |                                 |
   |        | rule are also set on   |                                 |
   |        | the link.  If all      |                                 |

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   |        | such colors are not    |                                 |
   |        | set on the link, the   |                                 |
   |        | link MUST be pruned    |                                 |
   |        | from the computation.  |                                 |
   +--------+------------------------+---------------------------------+
   | 5      | If the Flex-Algorithm  | Section 13 of [RFC9350]         |
   |        | Definition uses        |                                 |
   |        | something other than   |                                 |
   |        | the IGP metric         |                                 |
   |        | (Section 5 of          |                                 |
   |        | [RFC9350]), and such   |                                 |
   |        | metric is not          |                                 |
   |        | advertised for the     |                                 |
   |        | particular link in a   |                                 |
   |        | topology for which     |                                 |
   |        | the computation is     |                                 |
   |        | done, such link MUST   |                                 |
   |        | be pruned from the     |                                 |
   |        | computation.  A        |                                 |
   |        | metric of value 0      |                                 |
   |        | MUST NOT be assumed    |                                 |
   |        | in such a case.        |                                 |
   +--------+------------------------+---------------------------------+
   | 6      | Check if any exclude   | Section 6 of                    |
   |        | FAEMB rule is part of  | [I-D.ietf-lsr-flex-algo-bw-con] |
   |        | the Flex-Algorithm     |                                 |
   |        | definition.  If such   |                                 |
   |        | exclude rule exists    |                                 |
   |        | and the link has       |                                 |
   |        | Maximum Link           |                                 |
   |        | Bandwidth advertised,  |                                 |
   |        | check if the link      |                                 |
   |        | bandwidth satisfies    |                                 |
   |        | the FAEMB rule.  If    |                                 |
   |        | the link does not      |                                 |
   |        | satisfy the FAEMB      |                                 |
   |        | rule, the link MUST    |                                 |
   |        | be pruned from the     |                                 |
   |        | Flex-Algorithm         |                                 |
   |        | computation            |                                 |
   +--------+------------------------+---------------------------------+
   | 7      | Check if any exclude   | Section 6 of                    |
   |        | FAEMD rule is part of  | [I-D.ietf-lsr-flex-algo-bw-con] |
   |        | the Flex-Algorithm     |                                 |
   |        | definition.  If such   |                                 |
   |        | exclude rule exists    |                                 |
   |        | and the link has Min   |                                 |
   |        | Unidirectional link    |                                 |

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   |        | delay advertised,      |                                 |
   |        | check if the link      |                                 |
   |        | delay satisfies the    |                                 |
   |        | FAEMD rule.  If the    |                                 |
   |        | link does not satisfy  |                                 |
   |        | the FAEMD rule, the    |                                 |
   |        | link MUST be pruned    |                                 |
   |        | from the Flex-         |                                 |
   |        | Algorithm              |                                 |
   |        | computation.           |                                 |
   +--------+------------------------+---------------------------------+
   | 8      | Check if any exclude   | This document, Section 10       |
   |        | reverse Admin Group    |                                 |
   |        | rule is part of the    |                                 |
   |        | Flex-Algorithm         |                                 |
   |        | definition.  If such   |                                 |
   |        | exclude rule exists,   |                                 |
   |        | check if any Admin     |                                 |
   |        | Group that is part of  |                                 |
   |        | the exclude rule is    |                                 |
   |        | also set on the link   |                                 |
   |        | in the reverse         |                                 |
   |        | direction.  If such    |                                 |
   |        | Admin Group is set on  |                                 |
   |        | the link in the        |                                 |
   |        | reverse direction,     |                                 |
   |        | the link MUST be       |                                 |
   |        | pruned from the        |                                 |
   |        | computation.           |                                 |
   +--------+------------------------+---------------------------------+
   | 9      | Check if any include-  | This document, Section 10       |
   |        | any reverse Admin      |                                 |
   |        | Group rule is part of  |                                 |
   |        | the Flex-Algorithm     |                                 |
   |        | definition.  If such   |                                 |
   |        | include-any rule       |                                 |
   |        | exists, check if any   |                                 |
   |        | Admin Group that is    |                                 |
   |        | part of the include-   |                                 |
   |        | any rule is also set   |                                 |
   |        | on the link in the     |                                 |
   |        | reverse direction.     |                                 |
   |        | If no such Admin       |                                 |
   |        | Group is set on the    |                                 |
   |        | link in the reverse    |                                 |
   |        | direction, the link    |                                 |
   |        | MUST be pruned from    |                                 |
   |        | the computation        |                                 |

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   +--------+------------------------+---------------------------------+
   | 10     | Check if any include-  | This document, Section 10       |
   |        | all reverse Admin      |                                 |
   |        | Group rule is part of  |                                 |
   |        | the Flex-Algorithm     |                                 |
   |        | definition.  If such   |                                 |
   |        | include-all rule       |                                 |
   |        | exists, check if all   |                                 |
   |        | Admin Groups that are  |                                 |
   |        | part of the include-   |                                 |
   |        | all rule are also set  |                                 |
   |        | on the link in the     |                                 |
   |        | reverse direction.     |                                 |
   |        | If all such Admin      |                                 |
   |        | Groups are not set on  |                                 |
   |        | the link in the        |                                 |
   |        | reverse direction,     |                                 |
   |        | the link MUST be       |                                 |
   |        | pruned from the        |                                 |
   |        | computation.           |                                 |
   +--------+------------------------+---------------------------------+

               Table 6: IGP Flex-algo Path Calculation Rules

12.  Security Considerations

   This document inherits security considerations from [RFC9350].

13.  Acknowledgements

   TBD

14.  Normative References

   [I-D.ietf-lsr-flex-algo-bw-con]
              Hegde, S., Britto, W., Shetty, R., Decraene, B., Psenak,
              P., and T. Li, "Flexible Algorithms: Bandwidth, Delay,
              Metrics and Constraints", Work in Progress, Internet-
              Draft, draft-ietf-lsr-flex-algo-bw-con-18, 19 January
              2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
              lsr-flex-algo-bw-con-18>.

   [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>.

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Internet-Draft       Flex-Algorithm Reverse Affinity        January 2025

   [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>.

   [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>.

   [RFC9350]  Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
              and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
              DOI 10.17487/RFC9350, February 2023,
              <https://www.rfc-editor.org/info/rfc9350>.

Authors' Addresses

   Peter Psenak
   Cisco Systems
   Apollo Business Center
   Mlynske nivy 43
   82109 Bratislava
   Slovakia
   Email: ppsenak@cisco.com

   Jakub Horn
   Cisco Systems
   Milpitas, CA 95035
   United States of America
   Email: jakuhorn@cisco.com

   Amit Dhamija
   Arrcus
   Email: amitd@arrcus.com

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