



Internet Engineering Task Force (IETF)                         P. Psenak
Request for Comments: 9917                                       J. Horn
Updates: 9350, 9843                                        Cisco Systems
Category: Standards Track                                     A. Dhamija
ISSN: 2070-1721                                                   Arrcus
                                                            January 2026


          IGP Flexible Algorithms Reverse Affinity Constraint

Abstract

   An IGP Flexible Algorithm (Flex-Algorithm) enables the computation of
   constraint-based paths within an IGP domain, allowing operators to
   influence path selection according to administrative policies.  This
   document defines an extension to Flex-Algorithm that allows the
   inclusion or exclusion of links from path computation based on
   Administrative Groups (also known as link affinities) associated with
   the reverse direction of the path under computation.

   This document updates RFCs 9350 and 9843 by introducing the new IANA
   registry that specifies the ordered set of rules that are used to
   prune links from the topology during the Flex-Algorithm path
   computation.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9917.

Copyright Notice

   Copyright (c) 2026 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
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   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Requirements Language
   3.  Use Case Example
   4.  Deployment Consideration
   5.  IS-IS Flexible Algorithm Exclude Reverse Admin Group Sub-TLV
   6.  IS-IS Flexible Algorithm Include-Any Reverse Admin Group
           Sub-TLV
   7.  IS-IS Flexible Algorithm Include-All Reverse Admin Group
           Sub-TLV
   8.  OSPF Flexible Algorithm Exclude Reverse Admin Group Sub-TLV
   9.  OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV
   10. OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLV
   11. Calculation of Flexible Algorithm Paths
   12. IANA Considerations
     12.1.  Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV
     12.2.  OSPF Flexible Algorithm Definition TLV Sub-TLV Registry
     12.3.  IGP Flex-Algorithm Path Computation Rules Registry
       12.3.1.  Guidance for Designated Experts
   13. Security Considerations
   14. References
     14.1.  Normative References
     14.2.  Informative References
   Authors' Addresses

1.  Introduction

   IGP protocols historically computed the best paths over the network
   solely based on the IGP metric assigned to the links.  An IGP Flex-
   Algorithm as specified in [RFC9350] allows IGPs to compute
   constraint-based paths.  Several mechanisms to include or exclude the
   link during the Flex-Algorithm path calculation have been defined
   already:

   *  link inclusion or exclusion based on the presence of a specific
      Admin Group(s) [RFC9350]

   *  link exclusion based on the presence of a specific Shared Risk
      Link Group (SRLG) [RFC9350]

   *  link exclusion based on minimum bandwidth [RFC9843]

   *  link exclusion based on maximum delay [RFC9843]

   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 Shortest Path First
   (SPF) computation.

   This document updates [RFC9350] and [RFC9843] by creating the new
   IANA registry that specifies the ordered set of rules that are used
   to prune links from the topology during the Flex-Algorithm path
   computation (refer to Section 12.3.1).

   The term OSPF in this document is used to cover both OSPFv2 and
   OSPFv3 protocols.

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 (FAD) can specify Extended
   Administrative Groups that are used by the operator to include or
   exclude links during the Flex-Algorithm path computation [RFC9350].
   These link Extended Administrative Groups are checked in the path
   direction of the SPF computation, e.g., in the direction from the
   root vertex toward vertices of increasing distance.

   In certain scenarios, it is beneficial to evaluate the Extended
   Administrative Groups associated with the reverse direction of a
   link, rather than solely those in the direction of path computation.
   Consider a point-to-point link represented as a pair of directed
   edges between two nodes, A and B.  When computing a path from A to B,
   issues such as input errors on the link, detectable only at the
   receiving node B, may be operationally significant.  An operator
   might monitor metrics like Cyclic Redundancy Check (CRC) errors or
   other input-related faults at node B and apply thresholds over a
   defined observation period.  If such a threshold is exceeded, node B
   may locally assign specific Extended Administrative Groups to the
   link in the direction from B to A.

   To accommodate this operational intent, the Flex-Algorithm can be
   extended to inspect the Extended Administrative Groups of the
   reverse-direction edge (from B to A) when evaluating the forward-
   direction edge (from A to B) during path computation.  This enables
   the exclusion of links from the computed topology based on conditions
   detected at the far end of the link, improving network reliability
   and policy control.

4.  Deployment Consideration

   Threshold-based setting of the link Extended Administrative Groups
   must be done with care to avoid excessive flooding and constant Flex-
   Algorithm path recalculation.

   One possible approach is to use two different thresholds when setting
   and unsetting the Extended Administrative Group on the link.  For
   example, when setting the Extended Administrative Group on the link
   based on the percentage of certain incoming errors, higher threshold
   is used for setting and lower threshold is used for unsetting the
   Extended Administrative Group on the link.

   Many implementations provide a throttling mechanism that limits the
   rate at which the Link State PDU (LSP) in case of IS-IS, or Link
   State Advertisement (LSA) in case of OSPFv2 and OSPFv3, is updated at
   the originator.  Such mechanism is typically not specific to any
   particular link attribute, but rather considers any change in the LSP
   or LSA.  Application of such throttling mechanism can also be used to
   avoid frequent changes in the setting of the Extended Administrative
   Group on a link to affect the stability of the receivers.

5.  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 11.

   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:

   Type (1 octet):  10

   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.

6.  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 11.

   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 5.

   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.

7.  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 11.

   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 5.

   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.

8.  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 11.

   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):  10

   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.

9.  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 11.

   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 8.

   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.

10.  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 11.

   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 8.

   IANA has assigned Type value of 12 for the 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.

11.  Calculation of Flexible Algorithm Paths

   The following procedures augment the rules defined in Section 13 of
   [RFC9350] by introducing additional constraints based on
   Administrative Groups (AGs) associated with the reverse direction of
   a link.

   *  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 12.3 for these added rules.

12.  IANA Considerations

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

   IANA has registered the following in the "IS-IS Sub-Sub-TLVs for
   Flexible Algorithm Definition Sub-TLV" registry under the "IS-IS TLV
   Codepoints" registry group:

   Type:  10
   Description:  Flexible Algorithm Exclude Reverse Admin Group
   MP:  n
   Reference:  RFC 9917, Section 5

   Type:  11
   Description:  Flexible Algorithm Include-Any Reverse Admin Group
   MP:  n
   Reference:  RFC 9917, Section 6

   Type:  12
   Description:  Flexible Algorithm Include-All Reverse Admin Group
   MP:  n
   Reference:  RFC 9917, Section 7

12.2.  OSPF Flexible Algorithm Definition TLV Sub-TLV Registry

   This document makes the following registration in the "OSPF Flexible
   Algorithm Definition TLV Sub-TLVs" registry under the "Open Shortest
   Path First (OSPF) Parameters" registry group:

   Type:  10
   Description:  Flexible Algorithm Exclude Reverse Admin Group
   Reference:  RFC 9917, Section 8

   Type:  11
   Description:  Flexible Algorithm Include-Any Reverse Admin Group
   Reference:  RFC 9917, Section 9

   Type:  12
   Description:  Flexible Algorithm Include-All Reverse Admin Group
   Reference:  RFC 9917, Section 10

12.3.  IGP Flex-Algorithm Path Computation Rules Registry

   IANA has created a new registry called "IGP Flex-Algorithm Path
   Computation Rules" within the "Interior Gateway Protocol (IGP)
   Parameters" registry group.  The registration procedure for the new
   registry is Expert Review [RFC8126].  Section 12.3.1 provides
   guidance for designated experts.

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

   There is no upper bound on the number of rules that the registry
   supports.

   In Table 1, "FAEMB" means "Flex-Algorithm Exclude Minimum Bandwidth",
   and "FAEMD" means "Flex-Algorithm Exclude Maximum Delay".

   +==========+===========================================+===========+
   | Sequence | Description                               | Reference |
   | Number   |                                           |           |
   +==========+===========================================+===========+
   | 1        | Check if any exclude Administrative Group | Section   |
   |          | rule is part of the Flex-Algorithm        | 13 of     |
   |          | Definition.  If such exclude rule exists, | [RFC9350] |
   |          | check if any color 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 SRLG rule is part of | Section   |
   |          | the Flex-Algorithm Definition.  If such   | 13 of     |
   |          | exclude rule exists, check if the link is | [RFC9350] |
   |          | 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-any Administrative   | Section   |
   |          | Group rule is part of the Flex-Algorithm  | 13 of     |
   |          | Definition.  If such include-any rule     | [RFC9350] |
   |          | 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-all Administrative   | Section   |
   |          | Group rule is part of the Flex-Algorithm  | 13 of     |
   |          | Definition.  If such include-all rule     | [RFC9350] |
   |          | exists, check if all colors that are part |           |
   |          | of the include-all rule are also set on   |           |
   |          | the link.  If all such colors are not set |           |
   |          | on the link, the link MUST be pruned from |           |
   |          | the computation.                          |           |
   +----------+-------------------------------------------+-----------+
   | 5        | If the Flex-Algorithm Definition uses     | Section   |
   |          | something other than the IGP metric       | 13 of     |
   |          | (Section 5 of [RFC9350]), and such metric | [RFC9350] |
   |          | 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 FAEMB rule is part   | Section 6 |
   |          | of the Flex-Algorithm definition.  If     | of        |
   |          | such exclude rule exists and the link has | [RFC9843] |
   |          | 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 FAEMD rule is part   | Section 6 |
   |          | of the Flex-Algorithm definition.  If     | of        |
   |          | such exclude rule exists and the link has | [RFC9843] |
   |          | Min Unidirectional link 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 reverse Admin Group  | Section   |
   |          | rule is part of the Flex-Algorithm        | 11 of RFC |
   |          | definition.  If such exclude rule exists, | 9917      |
   |          | 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-any reverse Admin    | Section   |
   |          | Group rule is part of the Flex-Algorithm  | 11 of RFC |
   |          | definition.  If such include-any rule     | 9917      |
   |          | 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.              |           |
   +----------+-------------------------------------------+-----------+
   | 10       | Check if any include-all reverse Admin    | Section   |
   |          | Group rule is part of the Flex-Algorithm  | 11 of RFC |
   |          | definition.  If such include-all rule     | 9917      |
   |          | 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 1: IGP Flex-Algorithm Path Calculation Rules

12.3.1.  Guidance for Designated Experts

   Since the original Flex-Algorithm specification [RFC9350], many Flex-
   Algorithm extensions have been proposed and standardized.  Many of
   them added additional rules to the Flex-Algorithm path computation.
   Maintaining an IANA registry for these rules allows specification
   across multiple documents progressing independently.  The new "IGP
   Flex-Algorithm Path Computation Rules" registry has been created and
   is specified in Section 12.3.

   This section provides the guidance for designated experts on
   evaluating new registrations in the "IGP Flex-Algorithm Path
   Computation Rules" registry:

   1.  When a new constraint is defined, the rule associated with that
       constraint MAY be inserted at any position.  Backwards
       compatibility is guaranteed because nodes that don't support the
       new constraint will not participate in an algorithm where the FAD
       specifies a constraint they don't support.

   2.  The relative ordering of existing rules MUST NOT be altered.
       Doing so has the potential to create backwards compatibility
       issues.

   3.  Deletion of the rules MUST NOT be done.  Given that the rules are
       only used conditionally based on the information carried in the
       winning FAD, deletion of the rule is not necessary.

   4.  Merging or repeating of the rules MUST NOT be done.

13.  Security Considerations

   This document inherits security considerations from [RFC9350].

14.  References

14.1.  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>.

   [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>.

   [RFC9843]  Hegde, S., Britto, W., Shetty, R., Decraene, B., Psenak,
              P., and T. Li, "IGP Flexible Algorithms: Bandwidth, Delay,
              Metrics, and Constraints", RFC 9843, DOI 10.17487/RFC9843,
              September 2025, <https://www.rfc-editor.org/info/rfc9843>.

14.2.  Informative References

   [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

   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
