



Internet                                                           Y. Qu
Internet-Draft                                    Futurewei Technologies
Intended status: Standards Track                               A. Lindem
Expires: 15 March 2026                                          M. Joshi
                                                            Arrcus, Inc.
                                                       11 September 2025


   YANG Data Model for IS-IS Application-Specific Link Attributes and
                           Flexible Algorithm
                 draft-ietf-lsr-isis-flex-algo-yang-02

Abstract

   This document defines a YANG data model to support IS-IS Application-
   Specific Link Attributes and Flexible Algorithm.

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 15 March 2026.

Copyright Notice

   Copyright (c) 2025 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.  YANG Module for IS-IS Application-Specific Link Attributes  .   2
   3.  YANG Module for IS-IS Flexible Algorithm  . . . . . . . . . .  13
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  24
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  25
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .  25
   8.  Informative References  . . . . . . . . . . . . . . . . . . .  27
   Appendix A.  Example IS-IS Flex-Algo Configuration  . . . . . . .  27
   Appendix B.  Example IS-IS Flex-Algo Configuration (JSON) . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Overview

   This document defines two YANG [RFC7950] data modules.  The first
   module is to provide support for configuration and operational state
   for IS-IS Application-Specific Link Attributes as defined in
   [RFC9479], and the second module is to support IS-IS Flexible
   Algorithm as defined in [RFC9350].  Both modules are augmenting the
   IETF IS-IS YANG model [RFC9130].

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  YANG Module for IS-IS Application-Specific Link Attributes

   This document defined a YANG module for IS-IS Application-Specific
   Link Attributes as defined in [RFC9479].

   module: ietf-isis-link-attr
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/isis:isis:
       +--rw isis-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/isis:isis/isis:interfaces



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               /isis:interface:
       +--rw isis-asla
          +--rw interface-asla* [app-id]
             +--rw app-id                       uint16
             +--rw unidirectional-link-delay?   uint32
             +--rw metric-type?                 uint8
             +--rw metric?                      uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/isis:isis/isis:database
               /isis:levels/isis:lsp/isis:extended-is-neighbor
               /isis:neighbor/isis:instances/isis:instance:
       +--ro asla-sub-tlvs
          +--ro asla-sub-tlv* []
             +--ro l-flag?         boolean
             +--ro sabm-length?    uint8
             +--ro r-flag?         boolean
             +--ro udabm-length?   uint8
             +--ro sabm
             |  +--ro sabm-bits*   identityref
             +--ro udabm
             +--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/isis:isis/isis:database
               /isis:levels/isis:lsp/isis:mt-is-neighbor/isis:neighbor
               /isis:instances/isis:instance:
       +--ro asla-sub-tlvs
          +--ro asla-sub-tlv* []
             +--ro l-flag?         boolean
             +--ro sabm-length?    uint8
             +--ro r-flag?         boolean
             +--ro udabm-length?   uint8
             +--ro sabm
             |  +--ro sabm-bits*   identityref
             +--ro udabm
             +--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/isis:isis/isis:database
               /isis:levels/isis:lsp:
       +--ro application-specific-srlg-tlv
          +--ro as-srlg-tlv* []



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             +--ro neighbor-system-id?   isis:system-id
             +--ro pseudo-node-id?       uint8
             +--ro l-flag?               boolean
             +--ro sabm-length?          uint8
             +--ro r-flag?               boolean
             +--ro udabm-length?         uint8
             +--ro sabm
             |  +--ro sabm-bits*   identityref
             +--ro udabm
             +--ro length-of-sub-tlvs?   uint8
             +--ro link-id-sub-tlvs
             |  +--ro link-local-remote-ids
             |  |  +--ro link-local-id?    union
             |  |  +--ro link-remote-id?   union
             |  +--ro ipv4-interface-addr
             |  |  +--ro ipv4-int-addr?   inet:ipv4-address
             |  +--ro ipv4-neighbor-addr
             |  |  +--ro ipv4-neighbor-addr?   inet:ipv4-address
             |  +--ro ipv6-interface-addr
             |  |  +--ro ipv6-int-addr?   inet:ipv6-address
             |  +--ro ipv6-neighbor-addr
             |     +--ro ipv6-neighbor-addr?   inet:ipv6-address
             +--ro srlgs
                +--ro srlg*   uint32

   <CODE BEGINS> file "ietf-isis-link-attr@2025-09-11.yang"
   module ietf-isis-link-attr {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-isis-link-attr";
     prefix isis-link-attr;

     import ietf-inet-types {
       prefix inet;
       reference
         "RFC 6991: Common YANG Data Types";
     }
     import ietf-routing {
       prefix rt;
       reference
         "RFC 8349: A YANG Data Model for Routing
                    Management (NMDA Version)";
     }
     import ietf-isis {
       prefix isis;
       reference
         "RFC 9130: YANG Data Model for the IS-IS Protocol";
     }




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     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>
        Author:   Stephane Litkowski
                  <mailto:slitkows.ietf@gmail.com>
        Author:    Madhavi Joshi
                 <madhavi@arrcus.com>
       ";
     description
       "This YANG module defines the configuration and operational
        state for IS-IS application specific link attributes feature as
        defined in RFC 9479.

        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
        (http://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 2025-09-11 {
       description
         "Initial version";
       reference
         "RFC XXXX: YANG Data Model for IS-IS Application-Specific
                    Link Attributes and Flexible Algorithm";



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     }

     identity sabm-bit {
       description
         "Base identity for sabm bits.";
       reference
         "RFC 8919: IS-IS Application-Specific Link Attributes";
     }

     identity rsvp-te-bit {
       base sabm-bit;
       description
         "R bit, RSVP-TE.";
     }

     identity sr-policy-bit {
       base sabm-bit;
       description
         "S bit, Segment Routing Policy.";
     }

     identity lfa-bit {
       base sabm-bit;
       description
         "F bit, Loop Free Alternate (LFA). Includes all LFA types.";
     }

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

     grouping application-identifier-bit-mask {
       description
         "Identification of the set of applications associated with
          link attribute advertisements";
       leaf l-flag {
         type boolean;
         description
           "Legacy Flag. When set, all of the applications
            specified in the bit mask MUST use the legacy
            advertisements.";
       }
       leaf sabm-length {
         type uint8;



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         description
           "Standard Application Identifier Bit Mask Length in
            octets.";
       }
       leaf r-flag {
         type boolean;
         default "false";
         description
           "Reserved.";
       }
       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.";
       }
     }

     grouping application-specific-link-attributes-sub-tlv {
       description
         "Grouping for specification of the applications and
          application-specific attribute values.";
       container asla-sub-tlvs {
         list asla-sub-tlv {
           uses application-identifier-bit-mask;
           uses isis:unknown-tlvs;
           description
             "List of application specific link attributes sub-tlvs.";
         }



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         description
           "Application specific link attributes sub-tlv.";
       }
     }

     grouping application-specific-srlg-tlv {
       description
         "Grouping of a TLV to advertise application-specific
          SRLGs for a given link.";
       container application-specific-srlg-tlv {
         list as-srlg-tlv {
           leaf neighbor-system-id {
             type isis:system-id;
             description
               "Neighbor System-ID.";
           }
           leaf pseudo-node-id {
             type uint8;
             description
               "Pseudo-node ID.";
           }
           uses application-identifier-bit-mask;
           leaf length-of-sub-tlvs {
             type uint8;
             description
               "Length of sub-tlvs.";
           }
           container link-id-sub-tlvs {
             description
               "Link Identifier sub-TLVs.";
             container link-local-remote-ids {
               description
                 "Link local/remote identifier sub-tlv.";
               leaf link-local-id {
                 type union {
                   type inet:ipv4-address;
                   type uint32;
                 }
                 description
                   "Local identifier of the link.
                    It could be an IPv4 address or a local identifier.";
               }
               leaf link-remote-id {
                 type union {
                   type inet:ipv4-address;
                   type uint32;
                 }
                 description



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                   "Remote identifier of the link.
                    It could be an IPv4 address or a remotely learned
                    identifier.";
               }
             }
             container ipv4-interface-addr {
               leaf ipv4-int-addr {
                 type inet:ipv4-address;
                 description
                   "IPv4 address for the interface.";
               }
               description
                 "IPv4 interface address sub-tlv.";
             }
             container ipv4-neighbor-addr {
               leaf ipv4-neighbor-addr {
                 type inet:ipv4-address;
                 description
                   "IPv4 address for a neighboring router
                    on this link.";
               }
               description
                 "IPv4 neighbor address sub-tlv.";
             }
             container ipv6-interface-addr {
               leaf ipv6-int-addr {
                 type inet:ipv6-address;
                 description
                   "IPv6 address for the interface.";
               }
               description
                 "IPv6 interface address sub-tlv.";
             }
             container ipv6-neighbor-addr {
               leaf ipv6-neighbor-addr {
                 type inet:ipv6-address;
                 description
                   "IPv6 address for a neighboring router
                    on this link.";
               }
               description
                 "IPv6 neighbor address sub-tlv.";
             }
           }
           container srlgs {
             description
               "List of SRLGs.";
             leaf-list srlg {



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               type uint32;
               description
                 "SRLG value of the link.";
             }
           }
           description
             "List of application specific SRLG tlvs.";
         }
         description
           "Application specific SRLG tlv.";
       }
     }

     /* Configuration */

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis" {
       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used";
       }
       description
         "This augments ISIS protocol configuration
          with application specific link attributes.";
       container isis-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";
         }



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         description
           "Link attributes operation mode.";
       }
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis/isis:interfaces/isis:interface" {
       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/"
          + "rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used.";
       }
       description
         "This augments ISIS interface configuration
          with application specific link attributes.";
       container isis-asla {
         list interface-asla {
           key "app-id";
           leaf app-id {
             type uint16 {
               range "0 .. 1023";
             }
             description
               "Application ID.
                0 - RSVP TE. 1 - Segment Routing Policy.
                2 - Loop-Free Alternate.";
           }
           leaf unidirectional-link-delay {
             type uint32 {
               range "0 .. 16777215";
             }
             description
               "This 24-bit field carries the average link delay in
                microseconds.";
           }
           leaf metric-type {
             type uint8;
             description
               "IGP metric type.";
           }
           leaf metric {
             type uint32 {
               range "1 .. 16777215";
             }
             description
               "metric value.";



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           }
           description
             "ASLA interface configuration.";
         }
         description
           "Application specific link attributes configuration.";
       }
     }

     /* TLV 22 */

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis/isis:database/isis:levels/isis:lsp"
           + "/isis:extended-is-neighbor/isis:neighbor"
           + "/isis:instances/isis:instance" {
       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used";
       }
       description
         "This augments ISIS protocol LSDB TLV22.";
       uses application-specific-link-attributes-sub-tlv;
     }

     /* TLV 223 */

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis/isis:database/isis:levels/isis:lsp"
           + "/isis:mt-is-neighbor/isis:neighbor"
           + "/isis:instances/isis:instance" {
       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used";
       }
       description
         "This augments ISIS protocol LSDB TLV223.";
       uses application-specific-link-attributes-sub-tlv;
     }

     /* application-specific SRLG TLV 238 */

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis/isis:database/isis:levels/isis:lsp" {



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       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used";
       }
       description
         "This augments ISIS protocol LSDB.";
       uses application-specific-srlg-tlv;
     }
   }
   <CODE ENDS>

3.  YANG Module for IS-IS Flexible Algorithm

   This section defines the YANG module for IS-IS Flexible Algorithm.
   The module uses the identities defined in the IANA-maintained YANG
   modules for IGP Algorithm Types [IANA-IGP-ALGO-Types] and IGP Metric
   Type [IANA-IGP-Metric-Types] in [I-D.ietf-lsr-ospf-flex-algo-yang].

   module: ietf-isis-flex-algo
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/isis:isis:
       +--rw isis-flex-algo
          +--rw flex-algo* [algo-number]
             +--rw algo-number             uint8
             +--rw advertise-definition?   boolean
             +--rw admin-groups
             |       {te-types:extended-admin-groups,
             |        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 metric-type?            identityref
             +--rw calc-type?              identityref
             +--rw prefix-metric!
             +--rw priority?               uint8
     augment /rt:routing/rt:control-plane-protocols
                 /rt:control-plane-protocol/isis:isis
                 /isis:database/isis:levels/isis:lsp
                 /isis:router-capabilities:
       +--ro fad-tlvs
          +--ro fad-tlv* []
             +--ro flex-algo?              uint8
             +--ro metric-type?            identityref
             +--ro calc-type?              identityref



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             +--ro priority?               uint8
             +--ro fa-ex-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint64
             +--ro fa-in-any-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint64
             +--ro fa-in-all-ag-sub-tlv
             |  +--ro extended-admin-groups*   uint64
             +--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/isis:isis
             /isis:database/isis:levels/isis:lsp
             /isis:extended-ipv4-reachability/isis:prefixes:
       +--ro fapm-sub-tlvs
          +--ro fapm-sub-tlv* []
             +--ro flex-algo?   uint8
             +--ro metric?      uint32
     augment /rt:routing/rt:control-plane-protocols
             /rt:control-plane-protocol/isis:isis
             /isis:database/isis:levels/isis:lsp
             /isis:mt-extended-ipv4-reachability/isis:prefixes:
       +--ro fapm-sub-tlvs
          +--ro fapm-sub-tlv* []
             +--ro flex-algo?   uint8
             +--ro metric?      uint32
     augment /rt:routing/rt:control-plane-protocols
             /rt:control-plane-protocol/isis:isis
             /isis:database/isis:levels/isis:lsp
             /isis:ipv6-reachability/isis:prefixes:
       +--ro fapm-sub-tlvs
          +--ro fapm-sub-tlv* []
             +--ro flex-algo?   uint8
             +--ro metric?      uint32
     augment /rt:routing/rt:control-plane-protocols
             /rt:control-plane-protocol/isis:isis
             /isis:database/isis:levels/isis:lsp
             /isis:mt-ipv6-reachability/isis:prefixes:
       +--ro fapm-sub-tlvs
          +--ro fapm-sub-tlv* []
             +--ro flex-algo?   uint8
             +--ro metric?      uint32



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

   <CODE BEGINS> file "ietf-isis-flex-algo@2025-09-11.yang"
   module ietf-isis-flex-algo {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-isis-flex-algo";
     prefix isis-flex-algo;

     import ietf-routing {
       prefix rt;
       reference
         "RFC 8349: A YANG Data Model for Routing
                    Management (NMDA Version)";
     }
     import ietf-te-types {
       prefix te-types;
       reference
         "RFC8776: Common YANG Data Types for Traffic Engineering.";
     }
     import ietf-isis {
       prefix isis;
       reference
         "RFC 9130: YANG Data Model for the IS-IS Protocol";
     }
     import ietf-te {
       prefix te;
     }
     import iana-igp-algo-types {
       prefix iana-algo-types;
     }
     import iana-igp-metric-types {
       prefix iana-metric-type;
     }

     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



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                  <mailto:acee.ietf@gmail.com>
        Author:    Stephane Litkowski
                  <mailto:slitkows.ietf@gmail.com>
        Author:    Madhavi Joshi
                  <madhavi@arrcus.com>
       ";
     description
       "The YANG module defines the configuration and operational
        state for ISIS 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 2025-09-11 {
       description
         "Initial Version";
       reference
         "RFC XXXX: YANG Data Model for IS-IS Application-Specific
                    Link Attributes and Flexible Algorithm";
     }

     /* Identities */

     identity fad-flags {
       description
         "Base identity for ISIS FAD flags.";
     }

     identity m-bit {



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       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.";
     }

     /* Groupings */

     grouping fa-ex-ag-sub-tlv {
       container fa-ex-ag-sub-tlv {
         leaf-list extended-admin-groups {
           type uint64;
           description
             "Extended administrative group as defined in RFC 7308.";
         }
         description
           "The flex-algo exclude admin group sub-tlv.";
       }
       description
         "The flex-algo exclude admin group sub-tlv.";
     }

     grouping fa-in-any-ag-sub-tlv {
       container fa-in-any-ag-sub-tlv {
         leaf-list extended-admin-groups {
           type uint64;
           description
             "Extended administrative group as defined in RFC 7308.";
         }
         description
           "The flex-algo include-any admin group sub-tlv.";
       }
       description
         "The flex-algo include-any admin group sub-tlv.";
     }

     grouping fa-in-all-ag-sub-tlv {
       container fa-in-all-ag-sub-tlv {
         leaf-list extended-admin-groups {
           type uint64;
           description
             "Extended administrative group as defined in RFC 7308.";
         }
         description
           "The flex-algo include-all admin group sub-tlv.";
       }
       description



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         "The flex-algo include-all admin group sub-tlv.";
     }

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

     grouping fa-ex-srlg-sub-tlv {
       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.";
       }
       description
         "The flex-algo exclude SRLG sub-tlv.";
     }

     grouping fad-tlvs {
       container fad-tlvs {
         list fad-tlv {
           leaf flex-algo {
             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.";
           }



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           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
               "Priority of the advertisement.";
           }
           uses fa-ex-ag-sub-tlv;
           uses fa-in-any-ag-sub-tlv;
           uses fa-in-all-ag-sub-tlv;
           uses fad-flags-sub-tlv;
           uses fa-ex-srlg-sub-tlv;
           uses isis:unknown-tlvs;
           description
             "List of flex-algo definition TLVs.";
         }
         description
           "ISIS Flexible Algorithm Definition TLV.";
       }
       description
         "ISIS Flexible Algorithm Definition (FAD) TLV.";
     }

     grouping fapm-sub-tlvs {
       container fapm-sub-tlvs {
         list fapm-sub-tlv {
           leaf flex-algo {
             type uint8;
             description
               "Flex-algo number, value between 128 and 255
                inclusive.";
           }
           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.";
     }

     /* Configurations */

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis" {
       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used";
       }
       description
         "This augments ISIS protocol configuration
          with flexible algorithm.";
       container isis-flex-algo {
         list flex-algo {
           key "algo-number";
           leaf algo-number {
             type uint8 {
               range "128..255";
             }
             description
               "An identifier in the range 128-255 that's 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.";
             }



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             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.";
           }
           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 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;
             }
             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.";
           }



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           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 */

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis/isis:database/isis:levels/isis:lsp"
           + "/isis:router-capabilities" {
       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/"
          + "rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used";
       }
       description
         "This augments ISIS protocol LSDB router capability.";
       uses fad-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis/isis:database/isis:levels/isis:lsp"
           + "/isis:extended-ipv4-reachability/"
           + "isis:prefixes" {
       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/"
          + "rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used";
       }
       description
         "This augments ISIS protocol LSDB prefix.";



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       uses fapm-sub-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis/isis:database/isis:levels/isis:lsp"
           + "/isis:mt-extended-ipv4-reachability/isis:prefixes" {
       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/"
          + "rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used";
       }
       description
         "This augments ISIS protocol LSDB prefix.";
       uses fapm-sub-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis/isis:database/isis:levels/isis:lsp"
           + "/isis:ipv6-reachability/isis:prefixes" {
       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/"
          + "rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used";
       }
       description
         "This augments ISIS protocol LSDB prefix.";
       uses fapm-sub-tlvs;
     }

     augment "/rt:routing/"
           + "rt:control-plane-protocols/rt:control-plane-protocol"
           + "/isis:isis/isis:database/isis:levels/isis:lsp"
           + "/isis:mt-ipv6-reachability/isis:prefixes" {
       when "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/"
          + "rt:type = 'isis:isis'" {
         description
           "This augment ISIS routing protocol when used";
       }
       description
         "This augments ISIS protocol LSDB prefix.";
       uses fapm-sub-tlvs;
     }




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     /* notification */

     notification flex-algo-not-supported {
       uses isis:notification-instance-hdr;
       leaf flex-algo-number {
         type uint8 {
           range "128..255";
         }
         description
           "Flex-algo identifier which is not supported by the IS-IS
            instance.";
       }
       description
         "This notification is sent when an IS-IS instance does not
          support this flex-algo.";
     }
   }
   <CODE ENDS>

4.  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:

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

      /isis:isis/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.




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   Some of the readable data nodes in the modules 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.  The exposure of the Link State
   Database (LSDB) will expose the detailed topology of the network.
   This may be undesirable since both due to the fact that exposure may
   facilitate other attacks.  Additionally, network operators may
   consider their topologies to be sensitive confidential data.

5.  IANA Considerations

   This document registers a URI in the IETF XML registry [RFC3688].
   Following the format in [RFC3688], the following registrations are
   requested:

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

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

   This document registers the YANG module in the YANG Module Names
   registry [RFC7950].

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

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

6.  Acknowledgements

   Thanks to Michal Vasko for his YANG doctors review.

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

7.  Normative References





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   [I-D.ietf-lsr-ospf-flex-algo-yang]
              Qu, Y. and A. Lindem, "YANG Data Model for OSPF
              Application-Specific Link Attributes and Flexible
              Algorithm", Work in Progress, Internet-Draft, draft-ietf-
              lsr-ospf-flex-algo-yang-01, 7 September 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
              ospf-flex-algo-yang-01>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.





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   [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>.

   [RFC9130]  Litkowski, S., Ed., Yeung, D., Lindem, A., Zhang, J., and
              L. Lhotka, "YANG Data Model for the IS-IS Protocol",
              RFC 9130, DOI 10.17487/RFC9130, October 2022,
              <https://www.rfc-editor.org/info/rfc9130>.

   [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>.

   [RFC9479]  Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
              J. Drake, "IS-IS Application-Specific Link Attributes",
              RFC 9479, DOI 10.17487/RFC9479, October 2023,
              <https://www.rfc-editor.org/info/rfc9479>.

8.  Informative References

   [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 IS-IS Flex-Algo Configuration

   The following is an example configuration for IS-IS 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:isis="urn:ietf:params:xml:ns:yang:ietf-isis">\
             isis:isis</type>
           <name>isis</name>
           <isis xmlns="urn:ietf:params:xml:ns:yang:ietf-isis">
             <system-id>1111.2222.3333</system-id>
             <area-address>49.0001.0000.0000.0001</area-address>
             <isis-flex-algo xmlns="urn:ietf:params:xml:ns:yang:\
               ietf-isis-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>
             </isis-flex-algo>
           </isis>
         </control-plane-protocol>
       </control-plane-protocols>
     </routing>

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

   The following is an example configuration for IS-IS Flexible
   Algorithm in JSON format using the YANG model defined in this
   document.



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   {
     "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:isis": "urn:ietf:params:xml:ns:yang:ietf-isis",
             "__text": "isis:isis"
           },
           "name": "isis",
           "isis": {
             "system-id": "1111.2222.3333",
             "area-address": "49.0001.0000.0000.0001",
             "isis-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:yang:iana-igp-algo-types",
                   "__text": "iana-algo-types:algo-spf"
                 },
                 "prefix-metric": "",
                 "priority": "100"
               },
               "_xmlns": \
               "urn:ietf:params:xml:ns:yang:ietf-isis-flex-algo"
             },



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             "_xmlns": "urn:ietf:params:xml:ns:yang:ietf-isis"
           }
         }
       },
       "_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


   Madhavi Joshi
   Arrcus, Inc.
   United States of America
   Email: madhavi@arrcus.com

























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