



Internet                                                           Y. Qu
Internet-Draft                                    Futurewei Technologies
Intended status: Standards Track                               A. Lindem
Expires: 22 August 2026                                     Arrcus, Inc.
                                                        18 February 2026


   YANG Data Model for OSPF Application-Specific Link Attributes and
                           Flexible Algorithm
                 draft-ietf-lsr-ospf-flex-algo-yang-05

Abstract

   This document defines a YANG data model to support OSPF Application-
   Specific Link Attributes and Flexible Algorithm.  It also specifies
   the initial version of IANA-maintained YANG modules for IGP Algorithm
   Types and IGP Metric-Type.

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 22 August 2026.

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
   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.



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Table of Contents

   1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  IANA IGP Algorithm Types Module . . . . . . . . . . . . . . .   3
   3.  IANA IGP Metric Types Module  . . . . . . . . . . . . . . . .   5
   4.  YANG Module for OSPF Application-Specific Link Attributes . .   7
   5.  YANG Module for OSPF Flexible Algorithm . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  34
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
     7.1.  Registering YANG Modules  . . . . . . . . . . . . . . . .  35
     7.2.  IANA IGP Algorithm Types Module . . . . . . . . . . . . .  36
     7.3.  IANA IGP Metric-Type Module . . . . . . . . . . . . . . .  37
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  38
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  38
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  38
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  39
   Appendix A.  Example OSPF Flex-Algo Configuration (XML) . . . . .  40
   Appendix B.  Example OSPF Flex-Algo Configuration (JSON)  . . . .  42
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  43

1.  Overview

   This document defines YANG [RFC7950] data modules augmenting the IETF
   OSPF YANG model [RFC9129], which itself augments the IETF Routing
   model [RFC8349], to provide support for both OSPF Flexible Algorithm
   as defined in [RFC9350] and OSPF Application-Specific Link Attributes
   as defined in [RFC9492].

   Four YANG modules defined in this document.  The first is the initial
   version of the IANA-maintained YANG module for IGP Algorithm Types.
   The second module is the initial version of the IANA-maintained YANG
   module for IGP Metric-Type.  The third module augments the IETF OSPF
   YANG data model to support OSPF Flexible Algorithm, and the fourth
   module is to support OSPF Application-Specific Link Attributes.

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.








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2.  IANA IGP Algorithm Types Module

   IANA has created a registry titled "IGP Algorithm Types" under the
   "Interior Gateway Protocol (IGP) Parameters" registry group to
   identify Algorithm Types.  Module iana-igp-algo-types is an IANA-
   maintained module, which defines the identities for the Algorithm
   Types as in the IANA "IGP Algorithm Types" registry.

   This module is maintained by IANA and will be updated if and when
   there is any change to the registry.

   This document defines the initial version of the IANA-maintained YANG
   module for Algorithm Types that mirrors the IANA "IGP Algorithm
   Types" registry [IANA-IGP-ALGO-Types].

   <CODE BEGINS> file "iana-igp-algo-types@2025-09-05.yang"
   module iana-igp-algo-types {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:iana-igp-algo-types";
     prefix iana-algo-types;

     organization
       "Internet Assigned Numbers Authority (IANA)";
     contact
       "Internet Assigned Numbers Authority

        ICANN
        12025 Waterfront Drive, Suite 300
        Los Angeles, CA 90094-2536
        United States of America

        Tel:    +1 310 301 5800
         <mailto:iana@iana.org>";
     description
       "The YANG module defines the identities for Interior Gateway
        Protocol (IGP) Algorithm Types.

        This YANG module is maintained by IANA and reflects the 'IGP
        Algorithm Types' registry.

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

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Revised BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents



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        (https://trustee.ietf.org/license-info).

        All revisions of IETF and IANA published modules can be found
        at the YANG Parameters registry group
        (https://www.iana.org/assignments/yang-parameters).

        This initial version of this YANG module is part of RFC XXXX
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
        for full legal notices.

        //RFC Ed.: replace XXXX with actual RFC number and remove
          this note

        The latest version of this YANG module is available at
        https://www.iana.org/assignments/yang-parameters.";

     revision 2025-09-05 {
       description
         "Initial Version";
       reference
         "RFC XXXX: YANG Data Model for OSPF Application-Specific
                    Link Attributes and Flexible Algorithm";
     }

     identity algo-type {
       description
         "Base identity for IGP Algorithm Type. The algorithm types
          are defined in IANA IGP Algorithm Types registry.";
     }

     identity algo-spf {
       base algo-type;
       description
         "Shortest Path First (SPF) algorithm based on link metric.";
       reference
         "RFC 8665: OSPF Extensions for Segment Routing";
     }

     identity algo-strict-spf {
       base algo-type;
       description
         "Strict Shortest Path First (SPF) algorithm based on link
          metric.";
       reference
         "RFC 8665: OSPF Extensions for Segment Routing";
     }
   }
   <CODE ENDS>



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3.  IANA IGP Metric Types Module

   IANA has created a registry titled "IGP Metric-Type" under the
   "Interior Gateway Protocol (IGP) Parameters" registry group to
   identify Metric Types.  Module iana-igp-metric-types is an IANA-
   maintained module, which defines the identities for the Metric Types
   as in the IANA "IGP Metric-Type" registry.

   This module is maintained by IANA and will be updated if and when
   there is any change to the registry.

   This document defines the initial version of the IANA-maintained YANG
   module for Algorithm Types that mirrors the IANA "IGP Metric-Type"
   registry [IANA-IGP-Metric-Types].

   <CODE BEGINS> file "iana-igp-metric-types@2025-09-05.yang"
   module iana-igp-metric-types {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:iana-igp-metric-types";
     prefix iana-metric-types;

     organization
       "Internet Assigned Numbers Authority (IANA)";
     contact
       "Internet Assigned Numbers Authority

        ICANN
        12025 Waterfront Drive, Suite 300
        Los Angeles, CA 90094-2536
        United States of America

        Tel:    +1 310 301 5800
         <mailto:iana@iana.org>";
     description
       "The YANG module defines the identities for Interior Gateway
        Protocol (IGP) Metric-Types.

        This YANG module is maintained by IANA and reflects the 'IGP
        Metric-Type' registry.

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

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Revised BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents



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        (https://trustee.ietf.org/license-info).

        All revisions of IETF and IANA published modules can be found
        at the YANG Parameters registry group
        (https://www.iana.org/assignments/yang-parameters).

        This initial version of this YANG module is part of RFC XXXX
        (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
        for full legal notices.

        //RFC Ed.: replace XXXX with actual RFC number and remove
          this note

        The latest version of this YANG module is available at
        https://www.iana.org/assignments/yang-parameters.";

     revision 2025-09-05 {
       description
         "Initial Version";
       reference
         "RFC XXXX: YANG Data Model for OSPF Application-Specific
                    Link Attributes and Flexible Algorithm";
     }

     identity metric-type {
       description
         "Base identity for IGP Metric-Type. The metric types
          are defined in IANA IGP Metric-Type registry.";
     }

     identity igp-metric {
       base metric-type;
       description
         "IGP Metric.";
       reference
         "RFC9350: IGP Flexible Algorithm";
     }

     identity min-unidirectional-link-delay {
       base metric-type;
       description
         "Min Unidirectional Link Delay as defined in RFC8570
          Section 4.2 and RFC7471 Section 4.2.";
       reference
         "RFC9350: IGP Flexible Algorithm";
     }

     identity te-default-metric {



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       base metric-type;
       description
         "Traffic Engineering Default Metric as defined in RFC5305
          Section 3.7 and Traffic Engineering Metric as defined in
          RFC3630, Section 2.5.5.";
       reference
         "RFC9350: IGP Flexible Algorithm";
     }

     identity bandwidth-metric {
       base metric-type;
       description
         "Bandwidth metric.";
       reference
         "draft-ietf-lsr-flex-algo-bw-con";
     }
   }
   <CODE ENDS>

4.  YANG Module for OSPF Application-Specific Link Attributes

   This document defined a YANG module for OSPF Application-Specific
   Link Attributes (ASLA) as defined in [RFC9492].

   The module augments OSPF router configuration with support for the
   ASLA operation mode, enabling interoperability during the transition
   from legacy advertisements to ASLA.  In addition, both the OSPFv2 and
   OSPFv3 link-state databases are augmented to include the TLVs defined
   in[RFC9492].

   module: ietf-ospf-link-attr
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf:
       +--rw ospf-link-attr
          +--rw (link-attr-op-mode)
             +--:(legacy)
             |  +--rw legacy?         empty
             +--:(transition)
             |  +--rw transition?     empty
             +--:(app-specific)
                +--rw app-specific?   empty
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv2/ospf:ospfv2/ospf:body/ospf:opaque
               /ospf:extended-link-opaque/ospf:extended-link-tlv:
       +--ro app-specific-link-attr-sub-tlvs



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          +--ro asla-sub-tlvs* []
             +--ro sabm-length?                    uint8
             +--ro udabm-length?                   uint8
             +--ro sabm
             |  +--ro sabm-bits*   identityref
             +--ro udabm
             +--ro link-attributes-sub-sub-tlvs
                +--ro unknown-tlvs
                   +--ro unknown-tlv* []
                      +--ro type?     uint16
                      +--ro length?   uint16
                      +--ro value?    yang:hex-string
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv3/ospf:ospfv3/ospf:body/ospfv3-e-lsa:e-router
               /ospfv3-e-lsa:e-router-tlvs/ospfv3-e-lsa:link-tlv:
       +--ro app-specific-link-attr-sub-tlvs
          +--ro asla-sub-tlvs* []
             +--ro sabm-length?                    uint8
             +--ro udabm-length?                   uint8
             +--ro sabm
             |  +--ro sabm-bits*   identityref
             +--ro udabm
             +--ro link-attributes-sub-sub-tlvs
                +--ro unknown-tlvs
                   +--ro unknown-tlv* []
                      +--ro type?     uint16
                      +--ro length?   uint16
                      +--ro value?    yang:hex-string


   <CODE BEGINS> file "ietf-ospf-link-attr@2025-09-05.yang"
   module ietf-ospf-link-attr {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-ospf-link-attr";
     prefix ospf-link-attr;

     import ietf-routing {
       prefix rt;
       reference
         "RFC 8349: A YANG Data Model for Routing
                    Management (NMDA Version)";
     }
     import ietf-ospf {
       prefix ospf;
       reference



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         "RFC 9129: YANG Data Model for the OSPF Protocol";
     }
     import ietf-ospfv3-extended-lsa {
       prefix ospfv3-e-lsa;
       reference
         "RFC 9587: YANG Data Model for OSPFv3 Extended Link
                    State Advertisements (LSAs)";
     }

     organization
       "IETF LSR - Link State Routing Working Group";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/lsr/>
        WG List:  <mailto:lsr@ietf.org>

        Author:   Yingzhen Qu
                  <mailto:yingzhen.ietf@gmail.com>
        Author:   Acee Lindem
                  <mailto:acee.ietf@gmail.com>
       ";
     description
       "This YANG module defines the configuration and operational
        state for OSPF application specific link attributes feature
        as defined in RFC 9492.

        This YANG model conforms to the Network Management
        Datastore Architecture (NMDA) as described in RFC 8342.

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

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Revised BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX;
        see the RFC itself for full legal notices.";


     revision 2025-09-05 {
       description
         "Initial version";
       reference
         "RFC XXXX: YANG Data Model for OSPF Application-Specific
                    Link Attributes and Flexible Algorithm";



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     }

     identity sabm-bit {
       description
         "Base identity for SABM bits.";
       reference
         "RFC 9492: OSPF Application-Specific Link Attributes";
     }

     identity rsvp-te-bit {
       base sabm-bit;
       description
         "R bit, RSVP-TE.";
       reference
         "RFC 9492: OSPF Application-Specific Link Attributes";
     }

     identity sr-policy-bit {
       base sabm-bit;
       description
         "S bit, Segment Routing Policy.";
       reference
         "RFC 9492: OSPF Application-Specific Link Attributes";
     }

     identity lfa-bit {
       base sabm-bit;
       description
         "F bit, Loop Free Alternate (LFA). Includes all LFA types.";
       reference
         "RFC 9492: OSPF Application-Specific Link Attributes";
     }

     identity flex-algo-bit {
       base sabm-bit;
       description
         "X bit, flexible algorithm.";
       reference
         "RFC 9350: IGP Flexible Algorithm, Section 12.";
     }

     grouping app-specific-link-attr-sub-tlvs {
       description
         "OSPF Application-Specific Link Attributes (ASLA) sub-TLV.
          The ASLA sub-TLV is a sub-TLV of the OSPFv2 Extended Link
          TLV (RFC7684) and OSPFv3 Router-Link TLV (RFC8362).";
       container app-specific-link-attr-sub-tlvs {
         description



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           "Application-Specific Link Attributes sub-TLV.";
         list asla-sub-tlvs {
           leaf sabm-length {
             type uint8;
             description
               "Standard Application Identifier Bit Mask Length in
                octets.";
           }
           leaf udabm-length {
             type uint8;
             description
               "User Defined Application Identifier Bit Mask Length
                in octets.";
           }
           container sabm {
             leaf-list sabm-bits {
               type identityref {
                 base sabm-bit;
               }
               description
                 "SABM bits list. This list will contain
                  identities for the bits which are set in the
                  SABA bits.";
             }
             description
               "Standard Application Identifier Bit Mask.";
           }
           container udabm {
             description
               "User Defined Application Identifier Bit Mask.
                This container is to be augmented by user defined
                applications.";
           }
           container link-attributes-sub-sub-tlvs {
             uses ospf:unknown-tlvs;
             description
               "Link Attributes sub-sub-TLVs.";
           }
           description
             "List of application-Specific Link Attributes sub-TLVs.";
         }
       }
       reference
         "RFC 9492: OSPF Application-Specific Link Attributes";
     }

     /* Configuration */




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     augment "/rt:routing/rt:control-plane-protocols"
           + "/rt:control-plane-protocol/ospf:ospf" {
       when "../rt:type = 'ospf:ospfv2' or "
          + "../rt:type = 'ospf:ospfv3'" {
         description
           "This augments the OSPF routing protocol when used.";
       }
       description
         "This augments OSPF protocol configuration
          with application-specific link attributes.";
       container ospf-link-attr {
         choice link-attr-op-mode {
           mandatory true;
           leaf legacy {
             type empty;
             description
               "Only send legacy advertisements.";
           }
           leaf transition {
             type empty;
             description
               "Send both application-specific and legacy
                advertisements.";
           }
           leaf app-specific {
             type empty;
             description
               "Only send application-specific advertisements.";
           }
           description
             "Link attributes mode";
         }
         description
           "Link attributes operation mode.";
       }
     }

     /* Database */

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/"
           + "ospf:area/ospf:database/"
           + "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
           + "ospf:area-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque/"
           + "ospf:extended-link-opaque/ospf:extended-link-tlv" {
       when "derived-from(/rt:routing/rt:control-plane-protocols/"



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          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "OSPF Application-Specific Link Attributes (ASLA) sub-TLV is
          a sub-TLV of OSPFv2 Extended Link TLV (RFC7684).";
       uses app-specific-link-attr-sub-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/ospf:area/ospf:database/"
           + "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
           + "ospf:area-scope-lsa/ospf:version/ospf:ospfv3/"
           + "ospf:ospfv3/ospf:body/ospfv3-e-lsa:e-router/"
           + "ospfv3-e-lsa:e-router-tlvs/ospfv3-e-lsa:link-tlv" {
       when "derived-from(/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type, 'ospf:ospfv3')" {
         description
           "This augmentation is only valid for OSPFv3
            E-Router LSAs";
       }
       description
         "Augment OSPFv3 Area scope router-link TLV.";
       uses app-specific-link-attr-sub-tlvs;
     }
   }
   <CODE ENDS>

5.  YANG Module for OSPF Flexible Algorithm

   This document defines a YANG module for OSPF Flexible Algorithm as
   defined in [RFC9350].  It is an augmentation of the OSPF base model.

   The module augments OSPF router configuration with support flexible
   algorithms.  In addition, both the OSPFv2 and OSPFv3 link-state
   databases are augmented to include the TLVs defined in[RFC9350].

   module: ietf-ospf-flex-algo
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf:
       +--rw ospf-flex-algo
          +--rw flex-algo* [algo-number]
             +--rw algo-number             uint8
             +--rw advertise-definition?   boolean
             +--rw admin-groups
             |       {te-types:extended-admin-groups,



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             |        te-types:named-extended-admin-groups}?
             |  +--rw exclude-admin-groups*       leafref
             |  +--rw include-any-admin-groups*   leafref
             |  +--rw include-all-admin-groups*   leafref
             +--rw exclude-srlgs*
             |       -> /te:te/globals/named-srlgs/named-srlg/name
             |       {te-types:named-srlg-groups}?
             +--rw calc-type?              identityref
             +--rw metric-type?            identityref
             +--rw prefix-metric!
             +--rw priority?               uint8
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:interfaces/ospf:interface/ospf:database
               /ospf:link-scope-lsa-type/ospf:link-scope-lsas
               /ospf:link-scope-lsa/ospf:version/ospf:ospfv2/ospf:ospfv2
               /ospf:body/ospf:opaque/ospf:ri-opaque:
       +--ro fad-tlvs
          +--ro fad-tlv* []
             +--ro algo-number?            uint8
             +--ro metric-type?            identityref
             +--ro calc-type?              identityref
             +--ro priority?               uint8
             +--ro fa-ex-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-any-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-all-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fad-flags-sub-tlv
             |  +--ro fad-flags*   identityref
             +--ro fa-ex-srlg-sub-tlv
             |  +--ro srlgs*   uint32
             +--ro unknown-tlvs
                +--ro unknown-tlv* []
                   +--ro type?     uint16
                   +--ro length?   uint16
                   +--ro value?    yang:hex-string
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv2/ospf:ospfv2/ospf:body/ospf:opaque
               /ospf:ri-opaque:
       +--ro fad-tlvs
          +--ro fad-tlv* []
             +--ro algo-number?            uint8
             +--ro metric-type?            identityref



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             +--ro calc-type?              identityref
             +--ro priority?               uint8
             +--ro fa-ex-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-any-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-all-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fad-flags-sub-tlv
             |  +--ro fad-flags*   identityref
             +--ro fa-ex-srlg-sub-tlv
             |  +--ro srlgs*   uint32
             +--ro unknown-tlvs
                +--ro unknown-tlv* []
                   +--ro type?     uint16
                   +--ro length?   uint16
                   +--ro value?    yang:hex-string
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:database
               /ospf:as-scope-lsa-type/ospf:as-scope-lsas
               /ospf:as-scope-lsa/ospf:version/ospf:ospfv2/ospf:ospfv2
               /ospf:body/ospf:opaque/ospf:ri-opaque:
       +--ro fad-tlvs
          +--ro fad-tlv* []
             +--ro algo-number?            uint8
             +--ro metric-type?            identityref
             +--ro calc-type?              identityref
             +--ro priority?               uint8
             +--ro fa-ex-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-any-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-all-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fad-flags-sub-tlv
             |  +--ro fad-flags*   identityref
             +--ro fa-ex-srlg-sub-tlv
             |  +--ro srlgs*   uint32
             +--ro unknown-tlvs
                +--ro unknown-tlv* []
                   +--ro type?     uint16
                   +--ro length?   uint16
                   +--ro value?    yang:hex-string
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:interfaces/ospf:interface/ospf:database
               /ospf:link-scope-lsa-type/ospf:link-scope-lsas
               /ospf:link-scope-lsa/ospf:version/ospf:ospfv3/ospf:ospfv3



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               /ospf:body/ospf:router-information:
       +--ro fad-tlvs
          +--ro fad-tlv* []
             +--ro algo-number?            uint8
             +--ro metric-type?            identityref
             +--ro calc-type?              identityref
             +--ro priority?               uint8
             +--ro fa-ex-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-any-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-all-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fad-flags-sub-tlv
             |  +--ro fad-flags*   identityref
             +--ro fa-ex-srlg-sub-tlv
             |  +--ro srlgs*   uint32
             +--ro unknown-tlvs
                +--ro unknown-tlv* []
                   +--ro type?     uint16
                   +--ro length?   uint16
                   +--ro value?    yang:hex-string
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv3/ospf:ospfv3/ospf:body
               /ospf:router-information:
       +--ro fad-tlvs
          +--ro fad-tlv* []
             +--ro algo-number?            uint8
             +--ro metric-type?            identityref
             +--ro calc-type?              identityref
             +--ro priority?               uint8
             +--ro fa-ex-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-any-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-all-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fad-flags-sub-tlv
             |  +--ro fad-flags*   identityref
             +--ro fa-ex-srlg-sub-tlv
             |  +--ro srlgs*   uint32
             +--ro unknown-tlvs
                +--ro unknown-tlv* []
                   +--ro type?     uint16
                   +--ro length?   uint16



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                   +--ro value?    yang:hex-string
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:database
               /ospf:as-scope-lsa-type/ospf:as-scope-lsas
               /ospf:as-scope-lsa/ospf:version/ospf:ospfv3/ospf:ospfv3
               /ospf:body/ospf:router-information:
       +--ro fad-tlvs
          +--ro fad-tlv* []
             +--ro algo-number?            uint8
             +--ro metric-type?            identityref
             +--ro calc-type?              identityref
             +--ro priority?               uint8
             +--ro fa-ex-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-any-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fa-in-all-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint32
             +--ro fad-flags-sub-tlv
             |  +--ro fad-flags*   identityref
             +--ro fa-ex-srlg-sub-tlv
             |  +--ro srlgs*   uint32
             +--ro unknown-tlvs
                +--ro unknown-tlv* []
                   +--ro type?     uint16
                   +--ro length?   uint16
                   +--ro value?    yang:hex-string
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:interfaces/ospf:interface/ospf:database
               /ospf:link-scope-lsa-type/ospf:link-scope-lsas
               /ospf:link-scope-lsa/ospf:version/ospf:ospfv2/ospf:ospfv2
               /ospf:body/ospf:opaque/ospf:extended-prefix-opaque
               /ospf:extended-prefix-tlv:
       +--ro fapm-sub-tlvs
          +--ro fapm-sub-tlv* []
             +--ro algo-number?   uint8
             +--ro fapm-flags*    identityref
             +--ro metric?        uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv2/ospf:ospfv2/ospf:body/ospf:opaque
               /ospf:extended-prefix-opaque/ospf:extended-prefix-tlv:
       +--ro fapm-sub-tlvs
          +--ro fapm-sub-tlv* []
             +--ro algo-number?   uint8



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             +--ro fapm-flags*    identityref
             +--ro metric?        uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:database
               /ospf:as-scope-lsa-type/ospf:as-scope-lsas
               /ospf:as-scope-lsa/ospf:version/ospf:ospfv2/ospf:ospfv2
               /ospf:body/ospf:opaque/ospf:extended-prefix-opaque
               /ospf:extended-prefix-tlv:
       +--ro fapm-sub-tlvs
          +--ro fapm-sub-tlv* []
             +--ro algo-number?   uint8
             +--ro fapm-flags*    identityref
             +--ro metric?        uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv3/ospf:ospfv3/ospf:body
               /ospfv3-e-lsa:e-inter-area-prefix
               /ospfv3-e-lsa:e-inter-prefix-tlvs
               /ospfv3-e-lsa:inter-prefix-tlv:
       +--ro fapm-sub-tlvs
          +--ro fapm-sub-tlv* []
             +--ro algo-number?   uint8
             +--ro fapm-flags*    identityref
             +--ro metric?        uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:database
               /ospf:as-scope-lsa-type/ospf:as-scope-lsas
               /ospf:as-scope-lsa/ospf:version/ospf:ospfv3/ospf:ospfv3
               /ospf:body/ospfv3-e-lsa:e-as-external
               /ospfv3-e-lsa:e-external-tlvs
               /ospfv3-e-lsa:external-prefix-tlv:
       +--ro fapm-sub-tlvs
          +--ro fapm-sub-tlv* []
             +--ro algo-number?   uint8
             +--ro fapm-flags*    identityref
             +--ro metric?        uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv2/ospf:ospfv2/ospf:body/ospf:opaque:
       +--ro eia-asbr-opaque
          +--ro eia-asbr-tlv
          |  +--ro asbr-rtr-id?     rt-types:router-id
          |  +--ro faam-sub-tlvs
          |  |  +--ro faam-sub-tlv* []



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          |  |     +--ro algo-number?   uint8
          |  |     +--ro metric?        uint32
          |  +--ro unknown-tlvs
          |     +--ro unknown-tlv* []
          |        +--ro type?     uint16
          |        +--ro length?   uint16
          |        +--ro value?    yang:hex-string
          +--ro unknown-tlvs
             +--ro unknown-tlv* []
                +--ro type?     uint16
                +--ro length?   uint16
                +--ro value?    yang:hex-string
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
               /ospf:database/ospf:area-scope-lsa-type
               /ospf:area-scope-lsas/ospf:area-scope-lsa/ospf:version
               /ospf:ospfv3/ospf:ospfv3/ospf:body
               /ospfv3-e-lsa:e-inter-area-router
               /ospfv3-e-lsa:e-inter-router-tlvs
               /ospfv3-e-lsa:inter-router-tlv:
       +--ro faam-sub-tlvs
          +--ro faam-sub-tlv* []
             +--ro algo-number?   uint8
             +--ro metric?        uint32

     notifications:
       +---n flex-algo-not-supported
          +--ro routing-protocol-name?   leafref
          +--ro algo-number?             uint8

   <CODE BEGINS> file "ietf-ospf-flex-algo@2025-10-06.yang"
   module ietf-ospf-flex-algo {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-ospf-flex-algo";
     prefix ospf-flex-algo;

     import ietf-routing {
       prefix rt;
       reference
         "RFC 8349: A YANG Data Model for Routing
          Management (NMDA Version)";
     }
     import ietf-routing-types {
       prefix rt-types;
       reference
         "RFC 8294: Common YANG Data Types for the
          Routing Area";
     }



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     import ietf-te-types {
       prefix te-types;
       reference
         "RFC8776: Common YANG Data Types for Traffic Engineering.";
     }
     import ietf-ospf {
       prefix ospf;
       reference
         "RFC 9129: YANG Data Model for the OSPF
          Protocol";
     }
     import ietf-ospfv3-extended-lsa {
       prefix ospfv3-e-lsa;
       reference
         "RFC 9587: YANG Data Model for OSPFv3 Extended Link
          State Advertisements (LSAs)";
     }
     import ietf-te {
       prefix te;
       reference
         "draft-ietf-teas-yang-te";
     }
     import iana-igp-algo-types {
       prefix iana-algo-types;
       reference
         "RFC XXXX: YANG Data Model for OSPF Application-Specific
                    Link Attributes and Flexible Algorithm";
     }
     import iana-igp-metric-types {
       prefix iana-metric-type;
       reference
         "RFC XXXX: YANG Data Model for OSPF Application-Specific
                    Link Attributes and Flexible Algorithm";
     }

     organization
       "IETF LSR - Link State Routing Working Group";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/lsr/>
        WG List:  <mailto:lsr@ietf.org>


        Author:    Yingzhen Qu
                  <mailto:yingzhen.ietf@gmail.com>
        Author:    Acee Lindem
                  <mailto:acee.ietf@gmail.com>
       ";
     description



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       "The YANG module defines the configuration and operational
        state for OSPF Flexible Algorithm as defined in RFC 9350.

        This YANG model conforms to the Network Management
        Datastore Architecture (NMDA) as described in RFC 8342.

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

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, the Revised BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (https://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX;
        see the RFC itself for full legal notices.

        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 (RFC 2119) (RFC 8174) when, and only when,
        they appear in all capitals, as shown here.";

     revision 2025-10-06 {
       description
         "Initial Version";
       reference
         "RFC XXXX: YANG Data Model for OSPF Application-Specific
                    Link Attributes and Flexible Algorithm";
     }

     /* Identities */

     identity fad-flags {
       description
         "Base identity for OSPF FAD flags.";
       reference
         "RFC 9350: IGP Flexible Algorithm";
     }

     identity m-bit {
       base fad-flags;
       description
         "M bit, when set, the flex-algo specific prefix and ASBR
          metric MUST be used for inter-area and external prefix
          calculation.";



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       reference
         "RFC 9350: IGP Flexible Algorithm";
     }

     identity fapm-flags {
       description
         "Base identity for OSPF flex-algo prefix metric flags.";
       reference
         "RFC 9350: IGP Flexible Algorithm";
     }

     identity e-bit {
       base fapm-flags;
       description
         "External metric, if set, the metric specified is a
          type 2 external metric.";
       reference
         "RFC 9350: IGP Flexible Algorithm";
     }

     /* Groupings */
     grouping fad-tlvs {
       container fad-tlvs {
         list fad-tlv {
           leaf algo-number {
             type uint8;
             description
               "Flex-algo number, value between 128 and 255 inclusive.";
           }
           leaf metric-type {
             type identityref {
               base iana-metric-type:metric-type;
             }
             description
               "Type of metric to be used during the calculation.";
           }
           leaf calc-type {
             type identityref {
               base iana-algo-types:algo-type;
             }
             description
               "IGP algorithm types, value from 0 to 127 as
                defined under 'Interior Gateway Protocol (IGP)
                Parameter' by IANA.";
           }
           leaf priority {
             type uint8;
             description



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               "Priority of the advertisement.";
           }

           container fa-ex-ag-sub-tlv {
             leaf-list extended-admin-groups {
               type uint32;
               description
                 "Extended administrative group as defined in
                  RFC 7308.";
             }
             description
               "The flex-algo exclude admin group sub-tlv.";
           }

           container fa-in-any-ag-sub-tlv {
             leaf-list extended-admin-groups {
               type uint32;
               description
                 "Extended administrative group as defined in
                  RFC 7308.";
             }
             description
               "The flex-algo include-any admin group sub-tlv.";
           }

           container fa-in-all-ag-sub-tlv {
             leaf-list extended-admin-groups {
               type uint32;
               description
                 "Extended administrative group as defined in
                  RFC 7308.";
             }
             description
               "The flex-algo include-all admin group sub-tlv.";
           }

           container fad-flags-sub-tlv {
             leaf-list fad-flags {
               type identityref {
                 base fad-flags;
               }
               description
                 "Flex-algo definition flags list.";
             }
             description
               "OSPF flex-algo definition flags.";
           }




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           container fa-ex-srlg-sub-tlv {
             leaf-list srlgs {
               type uint32;
               description
                 "SRLG value as defined in RFC 4203.";
             }
             description
               "The flex-algo exclude SRLG sub-tlv.";
           }

           uses ospf:unknown-tlvs;
           description
             "List of flex-algo definition TLVs.";
         }
         description
           "OSPF Flexible Algorithm Definition TLV.";
       }
       description
         "OSPF Flexible Algorithm Definition (FAD) TLV.";
       reference
         "RFC 9350: IGP Flexible Algorithm";
     }

     grouping fapm-sub-tlvs {
       container fapm-sub-tlvs {
         list fapm-sub-tlv {
           leaf algo-number {
             type uint8;
             description
               "Flex-algo number, value between 128 and 255
                inclusive.";
           }
           leaf-list fapm-flags {
             type identityref {
               base fapm-flags;
             }
             description
               "Flex-algo prefix metric flags list.";
           }
           leaf metric {
             type uint32;
             description
               "Prefix metric.";
           }
           description
             "List of flex-algo prefix sub-tlvs.";
         }
         description



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           "Flex-algo prefix metric sub-tlvs.";
       }
       description
         "Flexible Algorithm Prefix Metric (FAPM) sub-TLVs.";
       reference
         "RFC 9350: IGP Flexible Algorithm";
     }

     grouping faam-sub-tlvs {
       container faam-sub-tlvs {
         list faam-sub-tlv {
           leaf algo-number {
             type uint8;
             description
               "Flex-algo number, value between 128 and 255
                inclusive.";
           }
           leaf metric {
             type uint32;
             description
               "Prefix metric.";
           }
           description
             "List of faam sub-tlvs.";
         }
         description
           "Flexible Algorithm ASBR Metric (FAAM) Sub-TLVs.";
       }
       description
         "Flexible Algorithm ASBR Metric (FAAM) Sub-TLVs.";
       reference
         "RFC 9350: IGP Flexible Algorithm";
     }

     /* Configurations */

     augment "/rt:routing/rt:control-plane-protocols"
           + "/rt:control-plane-protocol/ospf:ospf" {
       when "../rt:type = 'ospf:ospfv2' or "
          + "../rt:type = 'ospf:ospfv3'" {
         description
           "This augments the OSPF routing protocol when used.";
       }
       description
         "This augments OSPF protocol with Flexible
          Algorithm.";
       container ospf-flex-algo {
         list flex-algo {



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           key "algo-number";
           leaf algo-number {
             type uint8 {
               range "128..255";
             }
             description
               "An identifier associated with the Flexible Algorithm
                Definition.";
           }
           leaf advertise-definition {
             type boolean;
             default "true";
             description
               "Enable to advertise the flex-algo definition.";
           }
           container admin-groups {
             if-feature "te-types:extended-admin-groups";
             if-feature "te-types:named-extended-admin-groups";
             leaf-list exclude-admin-groups {
               type leafref {
                 path "/te:te/te:globals/te:named-admin-groups/"
                    + "te:named-admin-group/te:name";
               }
               description
                 "Exclude rule used during the flex-algo
                  path computation.";
             }
             leaf-list include-any-admin-groups {
               type leafref {
                 path "/te:te/te:globals/te:named-admin-groups/"
                    + "te:named-admin-group/te:name";
               }
               description
                 "Include-any rule used during the flex-algo
                  path computation.";
             }
             leaf-list include-all-admin-groups {
               type leafref {
                 path "/te:te/te:globals/te:named-admin-groups/"
                    + "te:named-admin-group/te:name";
               }
               description
                 "Include-all rule used during the flex-algo
                  path computation.";
             }
             description
               "Specify links for the flex-algo path computation.";
           }



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           leaf-list exclude-srlgs {
             if-feature "te-types:named-srlg-groups";
             type leafref {
               path "/te:te/te:globals/te:named-srlgs/te:named-srlg/"
                  + "te:name";
             }
             description
               "Shared Risk Link Groups (SRLGs) to be excluded during
                the flex-algo path computation.";
           }
           leaf calc-type {
             type identityref {
               base iana-algo-types:algo-type;
             }
             default "iana-algo-types:algo-spf";
             description
               "Calcuation-type. Value from 0-127 inclusive from the
                IANA 'IGP Algorithm Types' registry defined under the
                'Interior Gateway Protocol (IGP) Parameters' registry.";
           }
           leaf metric-type {
             type identityref {
               base iana-metric-type:metric-type;
             }
             default iana-metric-type:igp-metric;
             description
               "Type of metric to be used during the calculation.";
           }
           container prefix-metric {
             presence "Use flex-algo specific prefix metric.";
             description
               "Use flex-algo prefix metric.";
           }
           leaf priority {
             type uint8;
             description
               "Priority of the advertisement.";
           }
           description
             "List of flex-algo configurations.";
         }
         description
           "Flexible Algorithm configuration.";
       }
     }

     /* Database */




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     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/ospf:area/"
           + "ospf:interfaces/ospf:interface/ospf:database/"
           + "ospf:link-scope-lsa-type/ospf:link-scope-lsas/"
           + "ospf:link-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque/ospf:ri-opaque" {
       when "../../../../../../../../../../../../../"
          + "rt:type = 'ospf:ospfv2'" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "Flex-algo definition TLVs for OSPFv2 type 9 opaque RI LSA.";
       uses fad-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/"
           + "ospf:area/ospf:database/"
           + "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
           + "ospf:area-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque/ospf:ri-opaque" {
       when "../../../../../../../../../../../"
          + "rt:type = 'ospf:ospfv2'" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "Flex-algo definition TLVs for OSPFv2 type 10 opaque RI LSA.";
       uses fad-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:database/"
           + "ospf:as-scope-lsa-type/ospf:as-scope-lsas/"
           + "ospf:as-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque/ospf:ri-opaque" {
       when "../../../../../../../../../"
          + "rt:type = 'ospf:ospfv2'" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "Flex-algo definition TLVs for OSPFv2 type 11 opaque RI LSA.";
       uses fad-tlvs;



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     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/ospf:area/"
           + "ospf:interfaces/ospf:interface/ospf:database/"
           + "ospf:link-scope-lsa-type/ospf:link-scope-lsas/"
           + "ospf:link-scope-lsa/ospf:version/ospf:ospfv3/"
           + "ospf:ospfv3/ospf:body/ospf:router-information" {
       when "../../../../../../../../../../../../"
          + "rt:type = 'ospf:ospfv3'" {
         description
           "This augmentation is only valid for OSPFv3.";
       }
       description
         "Flex-algo definition TLVs for OSPFv3 Router
          Information (RI) LSA.";
       uses fad-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/"
           + "ospf:area/ospf:database/"
           + "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
           + "ospf:area-scope-lsa/ospf:version/ospf:ospfv3/"
           + "ospf:ospfv3/ospf:body/ospf:router-information" {
       when "../../../../../../../../../../"
          + "rt:type = 'ospf:ospfv3'" {
         description
           "This augmentation is only valid for OSPFv3.";
       }
       description
         "Flex-algo definition TLVs for OSPFv3 Router
          Information (RI) LSA.";
       uses fad-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:database/"
           + "ospf:as-scope-lsa-type/ospf:as-scope-lsas/"
           + "ospf:as-scope-lsa/ospf:version/ospf:ospfv3/"
           + "ospf:ospfv3/ospf:body/ospf:router-information" {
       when "../../../../../../../../"
          + "rt:type = 'ospf:ospfv3'" {
         description
           "This augmentation is only valid for OSPFv3.";



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       }
       description
         "Flex-algo definition TLVs for OSPFv3 Router Information LSA.";
       uses fad-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/ospf:area/"
           + "ospf:interfaces/ospf:interface/ospf:database/"
           + "ospf:link-scope-lsa-type/ospf:link-scope-lsas/"
           + "ospf:link-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque/"
           + "ospf:extended-prefix-opaque/ospf:extended-prefix-tlv" {
       when "../../../../../../../../../../../../../../"
          + "rt:type = 'ospf:ospfv2'" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "Flex-algo prefix metric sub-TLVs for OSPFv2 extended
          prefix TLV in type 9 opaque LSA.";
       uses fapm-sub-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/"
           + "ospf:area/ospf:database/"
           + "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
           + "ospf:area-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque/"
           + "ospf:extended-prefix-opaque/ospf:extended-prefix-tlv" {
       when "../../../../../../../../../../../../"
          + "rt:type = 'ospf:ospfv2'" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "Flex-algo prefix metric sub-TLVs for OSPFv2 extended
          prefix TLV in type 10 opaque LSA.";
       uses fapm-sub-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:database/"
           + "ospf:as-scope-lsa-type/ospf:as-scope-lsas/"



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           + "ospf:as-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque/"
           + "ospf:extended-prefix-opaque/"
           + "ospf:extended-prefix-tlv" {
       when "../../../../../../../../../../"
          + "rt:type = 'ospf:ospfv2'" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "Flex-algo prefix metric sub-TLVs for OSPFv2 extended
          prefix TLV in type 11 opaque LSA.";
       uses fapm-sub-tlvs;
     }

     /* Flex-algo prefix metric Sub-TLV in OSPFv3 Inter-Area
        Prefix TLV */

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/ospf:area/ospf:database/"
           + "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
           + "ospf:area-scope-lsa/ospf:version/ospf:ospfv3/"
           + "ospf:ospfv3/ospf:body/ospfv3-e-lsa:e-inter-area-prefix/"
           + "ospfv3-e-lsa:e-inter-prefix-tlvs/"
           + "ospfv3-e-lsa:inter-prefix-tlv" {
       when "../../../../../../../../../../../../"
          + "rt:type = 'ospf:ospfv3'" {
         description
           "This augmentation is only valid for OSPFv3
            E-Router LSAs";
       }
       uses fapm-sub-tlvs;
       description
         "OSPFv3 Area-Scoped Inter-Area Prefix TLV.";
     }

     /* Flex-algo prefix metric Sub-TLV in OSPFv3 External Prefix TLV */

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:database/"
           + "ospf:as-scope-lsa-type/ospf:as-scope-lsas/"
           + "ospf:as-scope-lsa/ospf:version/ospf:ospfv3/"
           + "ospf:ospfv3/ospf:body/ospfv3-e-lsa:e-as-external/"
           + "ospfv3-e-lsa:e-external-tlvs/"
           + "ospfv3-e-lsa:external-prefix-tlv" {
       when "'ospf:../../../../../../../../../"



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          + "rt:type' = 'ospf:ospfv3'" {
         description
           "This augmentation is only valid for OSPFv3.";
       }
       uses fapm-sub-tlvs;
       description
         "OSPFv3 AS-Scoped External Prefix TLV.";
     }

     /* OSPFv2 Extended Inter-Area ASBR LSA */

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/"
           + "ospf:area/ospf:database/"
           + "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
           + "ospf:area-scope-lsa/ospf:version/ospf:ospfv2/"
           + "ospf:ospfv2/ospf:body/ospf:opaque" {
       when "../../../../../../../../../../"
          + "rt:type = 'ospf:ospfv2'" {
         description
           "This augmentation is only valid for OSPFv2.";
       }
       description
         "OSPFv2 Extended Inter-Area ASBR LSA in type 10
          opaque LSA.";
       container eia-asbr-opaque {
         container eia-asbr-tlv {
           leaf asbr-rtr-id {
             type rt-types:router-id;
             description
               "The OSPF Router ID of the ASBR.";
           }
           uses faam-sub-tlvs;
           uses ospf:unknown-tlvs;
           description
             "EIA-ASBR TLV, used to advertise additional attributes
              associated with the reachability of an ASBR.";
         }
         uses ospf:unknown-tlvs;
         description
           "OSPFv2 Extended Inter-Area (EIA-ASBR) opaque LSA.";
       }
     }

     /* FAAM Sub-TLV in OSPFv3 Inter-Area-Router TLV */

     augment "/rt:routing/"



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           + "rt:control-plane-protocols/rt:control-plane-protocol/"
           + "ospf:ospf/ospf:areas/ospf:area/ospf:database/"
           + "ospf:area-scope-lsa-type/ospf:area-scope-lsas/"
           + "ospf:area-scope-lsa/ospf:version/ospf:ospfv3/"
           + "ospf:ospfv3/ospf:body/ospfv3-e-lsa:e-inter-area-router/"
           + "ospfv3-e-lsa:e-inter-router-tlvs/"
           + "ospfv3-e-lsa:inter-router-tlv" {
       when "../../../../../../../../../../../../"
          + "rt:type = 'ospf:ospfv3'" {
         description
           "This augmentation is only valid for OSPFv3
            Inter-Area-Router TLV.";
       }
       uses faam-sub-tlvs;
       description
         "OSPFv3 Area-Scoped Inter-Area-Router TLV.";
     }

     /* notification */

     notification flex-algo-not-supported {
       leaf routing-protocol-name {
         type leafref {
           path "/rt:routing/rt:control-plane-protocols/"
              + "rt:control-plane-protocol/rt:name";
         }
         description
           "Name of the OSPF instance.";
       }
       leaf algo-number {
         type uint8;
         description
           "Flex-algo identifier which is not supported by the OSPF
            instance.";
       }
       description
         "This notification is sent when an OSPF instance does not
          support this flex-algo.";
     }
   }
   <CODE ENDS>










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6.  Security Considerations

   The YANG modules defined in this document are designed to be accessed
   via YANG-based management protocols, such as NETCONF [RFC6241] and
   RESTCONF [RFC8040].  These protocols have to use a secure transport
   layer (e.g., SSH [RFC4252], TLS [RFC8446], and QUIC [RFC9000]) and
   have to use mutual authentication.

   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., "config true", which is the
   default).  All writable data nodes are likely to be reasonably
   sensitive or vulnerable in some network environments.  Write
   operations (e.g., edit-config) and delete operations to these data
   nodes without proper protection or authentication can have a negative
   effect on network operations.  The following subtrees and data nodes
   have particular sensitivities/vulnerabilities:

      /ospf:ospf/ospf-link-attr/link-attr-op-mode - Modification to the
      protocol operation mode may result in traffic disruption.

      /ospf:ospf/flex-algo - Modification to flex-algo configuration
      could be used to mount a DoS attack.  For example, changing of
      calc-type may result in routing loops.

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.  Specifically, the following
   subtrees and data nodes have particular sensitivities/
   vulnerabilities:

      Both module ietf-ospf-flex-algo and module ietf-ospf-link-attr
      augments base OSPF module Link State Database (LSDB) with various
      TLVs.  Knowledge of these data nodes can be used to attack other
      routers in the OSPF domain.  These attacks are documented in
      [RFC9129].

7.  IANA Considerations








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7.1.  Registering YANG Modules

   This document registers URIs in the IETF XML registry [RFC3688].
   Following the format in [RFC3688], the following registrations are
   requested to be made:

      URI: urn:ietf:params:xml:ns:yang:iana-igp-algo-types
      Registrant Contact: The IESG.
      XML: N/A, the requested URI is an XML namespace.

      URI: urn:ietf:params:xml:ns:yang:iana-igp-metric-types
      Registrant Contact: The IESG.
      XML: N/A, the requested URI is an XML namespace.

      URI: urn:ietf:params:xml:ns:yang:ietf-ospf-link-attr
      Registrant Contact: The IESG.
      XML: N/A, the requested URI is an XML namespace.

      URI: urn:ietf:params:xml:ns:yang:ietf-ospf-flex-algo
      Registrant Contact: The IESG.
      XML: N/A, the requested URI is an XML namespace.

   This document registers the YANG modules in the YANG Module Names
   registry [RFC6020].

      name: iana-igp-algo-types
      Maintained by IANA?  Y
      namespace: urn:ietf:params:xml:ns:yang:iana-igp-algo-types
      prefix: iana-algo-types
      reference: RFC XXXX

      name: iana-igp-metric-types
      Maintained by IANA?  Y
      namespace: urn:ietf:params:xml:ns:yang:iana-igp-metric-types
      prefix: iana-metric-types
      reference: RFC XXXX

      name: ietf-ospf-link-attr
      Maintained by IANA?  N
      namespace: urn:ietf:params:xml:ns:yang:ietf-ospf-link-attr
      prefix: ospf-link-attr
      reference: RFC XXXX

      name: ietf-ospf-flex-algo
      Maintained by IANA?  N
      namespace: urn:ietf:params:xml:ns:yang:ietf-ospf-flex-algo
      prefix: ospf-flex-algo
      reference: RFC XXXX



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7.2.  IANA IGP Algorithm Types Module

   This document defines the initial version of the IANA-maintained
   "iana-algo-types" YANG module (Section 2).  The most recent version
   of the YANG module is available from the "YANG Parameters" registry
   [IANA-YANG-Parameters].

   IANA is requested to add this note to the registry:

   |  New values must not be directly added to the "iana-algo-types"
   |  YANG module.  They must instead be added to the "IGP Algorithm
   |  Types" registry in the "Interior Gateway Protocol (IGP)
   |  Parameters" registry group.

   When a value is added to the "IGP Algorithm Types" registry, a new
   "identity" statement needs to be added to the "iana-algo-types" YANG
   module.  The name of the "identity" MUST be the name as provided in
   the registry.  The "identity" statement should have the following
   sub-statements defined:

     "base":          contains "algo-type".
     "description":   Replicates the description from the registry.
     "reference":     Replicates the reference(s) from the registry with
                      the title of the document(s) added.

   When the "iana-algo-types" YANG module is updated, a new "revision"
   statement with a unique revision date must be added in front of the
   existing revision statements.  The "revision" statement MUST contain
   both "description" and "reference" substatements as follows.

   The "description" substatement captures what changed in the revised
   version.  Typically, the description enumerates the changes such as
   udpates to existing entries (e.g., update a description or a
   reference) or notes which identities were added or had their status
   changed (e.g., deprecated, discouraged, or obsoleted).

   The "reference" substatement points specifically to the published
   module (i.e., IANA_FOO_URL_With_REV).  It may also point to an
   authoritative event triggering the update to the YANG module.  In all
   cases, this event is cited from the underlying IANA registry.  If the
   update is triggered by an RFC, that RFC must also be included in the
   "reference" substatement.

   IANA is requested to add this note to [IANA-IGP-ALGO-Types]:

   |  When this registry is modified, the YANG module "iana-algo-types"
   |  Section 2 must be updated as defined in RFC XXXX.




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7.3.  IANA IGP Metric-Type Module

   This document defines the initial version of the IANA-maintained
   "iana-metric-types" YANG module (Section 3).  The most recent version
   of the YANG module is available from the "YANG Parameters" registry
   [IANA-YANG-Parameters].

   IANA is requested to add this note to the registry:

   |  New values must not be directly added to the "iana-metric-types"
   |  YANG module.  They must instead be added to the "IGP Metric-Type"
   |  registry in the "Interior Gateway Protocol (IGP) Parameters"
   |  registry group.

   When a value is added to the "IGP Metric-Type" registry, a new
   "identity" statement needs to be added to the "iana-metric-types"
   YANG module.  The name of the "identity" MUST be the name as provided
   in the registry.  The "identity" statement should have the following
   sub-statements defined:

     "base":          contains "metric-type".
     "description":   Replicates the description from the registry.
     "reference":     Replicates the reference(s) from the registry with
                      the title of the document(s) added.

   When the "iana-metric-types" YANG module is updated, a new "revision"
   statement with a unique revision date must be added in front of the
   existing revision statements.  The "revision" statement MUST contain
   both "description" and "reference" substatements as follows.

   The "description" substatement captures what changed in the revised
   version.  Typically, the description enumerates the changes such as
   udpates to existing entries (e.g., update a description or a
   reference) or notes which identities were added or had their status
   changed (e.g., deprecated, discouraged, or obsoleted).

   The "reference" substatement points specifically to the published
   module (i.e., IANA_FOO_URL_With_REV).  It may also point to an
   authoritative event triggering the update to the YANG module.  In all
   cases, this event is cited from the underlying IANA registry.  If the
   update is triggered by an RFC, that RFC must also be included in the
   "reference" substatement.

   IANA is requested to add this note to [IANA-IGP-Metric-Types]:

   |  When this registry is modified, the YANG module "iana-metric-
   |  types" Section 2 must be updated as defined in RFC XXXX.




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8.  Acknowledgements

   Thanks to Dhruv Dhody for his detailed YANG doctors review.

   The YANG model was developed using the suite of YANG tools written
   and maintained by numerous authors.

9.  References

9.1.  Normative References

   [IANA-IGP-ALGO-Types]
              IANA, "IGP Algorithm Types",
              <https://www.iana.org/assignments/igp-parameters>.

   [IANA-IGP-Metric-Types]
              IANA, "IGP Metric-Type",
              <https://www.iana.org/assignments/igp-parameters>.

   [IANA-YANG-Parameters]
              IANA, "YANG Module Names",
              <https://www.iana.org/assignments/yang-parameters>.

   [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>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.






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   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [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>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8349]  Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
              Routing Management (NMDA Version)", RFC 8349,
              DOI 10.17487/RFC8349, March 2018,
              <https://www.rfc-editor.org/info/rfc8349>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,
              <https://www.rfc-editor.org/info/rfc9000>.

   [RFC9129]  Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem,
              "YANG Data Model for the OSPF Protocol", RFC 9129,
              DOI 10.17487/RFC9129, October 2022,
              <https://www.rfc-editor.org/info/rfc9129>.

   [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>.

   [RFC9492]  Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
              J., and J. Drake, "OSPF Application-Specific Link
              Attributes", RFC 9492, DOI 10.17487/RFC9492, October 2023,
              <https://www.rfc-editor.org/info/rfc9492>.

9.2.  Informative References




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   [RFC8792]  Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
              "Handling Long Lines in Content of Internet-Drafts and
              RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
              <https://www.rfc-editor.org/info/rfc8792>.

Appendix A.  Example OSPF Flex-Algo Configuration (XML)

   The following is an example configuration for OSPF Flexible Algorithm
   using the YANG model defined in this document.

   Note: '\' line wrapping per [RFC8792].








































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   <?xml version='1.0' encoding='UTF-8'?>
     <te xmlns="urn:ietf:params:xml:ns:yang:ietf-te">
       <enable>true</enable>
       <globals>
         <named-admin-groups>
           <named-admin-group>
             <name>blue</name>
           </named-admin-group>
         </named-admin-groups>
       </globals>
     </te>
     <routing xmlns="urn:ietf:params:xml:ns:yang:ietf-routing">
       <router-id>1.1.1.1</router-id>
       <control-plane-protocols>
         <control-plane-protocol>
           <type xmlns:ospf="urn:ietf:params:xml:ns:yang:ietf-ospf">\
             ospf:ospfv2</type>
           <name>OSPFv2</name>
              <ospf xmlns="urn:ietf:params:xml:ns:yang:ietf-ospf">
                <areas>
                  <area>
                    <area-id>0.0.0.0</area-id>
                  </area>
                </areas>
             <ospf-flex-algo xmlns="urn:ietf:params:xml:ns:yang:\
               ietf-ospf-flex-algo">
               <flex-algo>
                 <algo-number>200</algo-number>
                 <admin-groups>
                   <exclude-admin-groups>blue</exclude-admin-groups>
                 </admin-groups>
                 <metric-type xmlns:iana-metric-types=\
                   "urn:ietf:params:xml:ns:yang:iana-igp-metric-types">\
                   iana-metric-types:igp-metric</metric-type>
                 <calc-type xmlns:iana-algo-types=\
                   "urn:ietf:params:xml:ns:yang:iana-igp-algo-types">\
                   iana-algo-types:algo-spf</calc-type>
                 <prefix-metric/>
                 <priority>100</priority>
               </flex-algo>
             </ospf-flex-algo>
           </ospf>
         </control-plane-protocol>
       </control-plane-protocols>
     </routing>






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Appendix B.  Example OSPF Flex-Algo Configuration (JSON)

   The following is the same example configuration for OSPF Flexible
   Algorithm as in the previous section in JSON format using the YANG
   model defined in this document.

   {
     "te": {
       "enable": "true",
       "globals": {
         "named-admin-groups": {
           "named-admin-group": {
             "name": "blue"
           }
         }
       },
       "_xmlns": "urn:ietf:params:xml:ns:yang:ietf-te"
     }
   }
   {
     "routing": {
       "router-id": "1.1.1.1",
       "control-plane-protocols": {
         "control-plane-protocol": {
           "type": {
             "_xmlns:ospf": "urn:ietf:params:xml:ns:yang:ietf-ospf",
             "__text": "ospf:ospfv2"
           },
           "name": "OSPFv2",
           "ospf": {
             "areas": {
               "area": {
                 "area-id": "0.0.0.0"
               }
             },
             "ospf-flex-algo": {
               "flex-algo": {
                 "algo-number": "200",
                 "admin-groups": {
                   "exclude-admin-groups": "blue"
                 },
                 "metric-type": {
                   "_xmlns:iana-metric-types": "urn:ietf:params:xml:ns:\
                   yang:iana-igp-metric-types",
                   "__text": "iana-metric-types:igp-metric"
                 },
                 "calc-type": {
                   "_xmlns:iana-algo-types": "urn:ietf:params:xml:ns:\



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                   yang:iana-igp-algo-types",
                   "__text": "iana-algo-types:algo-spf"
                 },
                 "prefix-metric": "",
                 "priority": "100"
               },
               "_xmlns": "urn:ietf:params:xml:ns:yang:\
               ietf-ospf-flex-algo"
             },
             "_xmlns": "urn:ietf:params:xml:ns:yang:ietf-ospf"
           }
         }
       },
       "_xmlns": "urn:ietf:params:xml:ns:yang:ietf-routing"
     }
   }

Authors' Addresses

   Yingzhen Qu
   Futurewei Technologies
   United States of America
   Email: yingzhen.ietf@gmail.com


   Acee Lindem
   Arrcus, Inc.
   United States of America
   Email: acee.ietf@gmail.com






















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