A YANG Network Data Model for Inventory Topology Mapping
draft-ietf-ivy-network-inventory-topology-06

Network Inventory YANG                                        B. Wu, Ed.
Internet-Draft                                                    Huawei
Intended status: Standards Track                            M. Boucadair
Expires: 1 September 2026                                         Orange
                                                                 C. Zhou
                                                            China Mobile
                                                                   Q. Wu
                                                                  Huawei
                                                        28 February 2026

        A YANG Network Data Model for Inventory Topology Mapping
              draft-ietf-ivy-network-inventory-topology-06

Abstract

   This document defines a YANG data model to map the network inventory
   data with the topology data to form a base underlay network.  The
   data model facilitates the correlation between the layer (e.g., Layer
   2 or Layer 3) topology information and the inventory data of the
   underlay network for better service provisioning, network maintenance
   operations, and other assessment scenarios.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Discussion of this document takes place on the Network Inventory YANG
   Working Group mailing list (inventory-yang@ietf.org), which is
   archived at https://mailarchive.ietf.org/arch/browse/inventory-yang/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ietf-ivy-wg/network-inventory-topology.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   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."

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   This Internet-Draft will expire on 1 September 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Editorial Note (To be removed by RFC Editor)  . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Sample Use Cases of the Data Model  . . . . . . . . . . . . .   4
     3.1.  Determine Available Resources of Service Attachment Points
           (SAPs)  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  "What-if" Scenarios . . . . . . . . . . . . . . . . . . .   4
   4.  Module Tree Structure . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Link Extensions . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Port-Breakout Capability  . . . . . . . . . . . . . . . .   6
   5.  Network Inventory Topology YANG Module  . . . . . . . . . . .   7
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  "link-type" Usage Examples . . . . . . . . . . . . .  15
   Appendix B.  JSON Example of an MPO Breakout-Channel Port . . . .  17
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

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1.  Introduction

   [I-D.ietf-ivy-network-inventory-yang] defines the base network
   inventory model to aggregate the inventory data of Network Elements
   (NEs).  This data includes identification of these NEs and their
   hardware, firmware, and software components.  Examples of inventory
   hardware components could be rack, shelf, slot, board, or physical
   port.  Examples of inventory software components could be platform
   Operating System (OS), software-modules, bios, or boot-loader
   [I-D.ietf-ivy-network-inventory-software].

   In order to ease navigation from (or to) inventory and network
   topologies, this document extends the network topology data model
   [RFC8345] for network inventory mapping: "ietf-network-inventory-
   topology" (Section 5).  This data model provides a mechanism for the
   correlation with existing network and topology data models, such as
   "A YANG Network Data Model for Service Attachment Points (SAPs)"
   [RFC9408], "A YANG Data Model for Layer 2 Network Topologies"
   [RFC8944], and "A YANG Data Model for Layer 3 Topologies" [RFC8346].

   Similar to the base inventory data model
   [I-D.ietf-ivy-network-inventory-yang], the network inventory topology
   does not make any assumption about involved NEs and their roles in
   topologies.  As such, the mapping model can be applied independent of
   the network type (optical local loops, access network, core network,
   etc.) and application.

1.1.  Editorial Note (To be removed by RFC Editor)

      Note to the RFC Editor: This section is to be removed prior to
      publication.

   This document contains placeholder values that need to be replaced
   with finalized values at the time of publication.  This note
   summarizes all of the substitutions that are needed.

   Please apply the following replacements:

   *  XXXX --> the assigned RFC number for this I-D

   *  AAAA --> the assigned RFC number for
      [I-D.ietf-ivy-network-inventory-yang]

2.  Conventions and Definitions

   The meanings of the symbols in the YANG tree diagrams are defined in
   [RFC8340].

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   This document uses terms defined in
   [I-D.ietf-ivy-network-inventory-yang].

3.  Sample Use Cases of the Data Model

3.1.  Determine Available Resources of Service Attachment Points (SAPs)

   The inventory topology data model can be used as a basis for
   correlating underlay information, such as physical port components.
   Figure 1 exemplifies this usage.

   During service provisioning, to check available physical port
   resources, the SAPs information can be associated with the underlay
   inventory information and interface information associated with the
   inventory topology, e.g., "parent-termination-point" of SAP Model can
   be associated with the "port-component-ref" of the inventory topology
   data model, which can be used to check the availability and capacity
   of physical ports.

                               +-----------------+
                               |     Customer    |
                               +--------+--------+
               Customer Service Models  |
                  (e.g., L3SM, L2SM)    |
                               +--------+--------+
                               |    Service      |
                               |  Orchestration  |
                               +------+---+------+
                                      |   |
                    SAP Network Model |   | Inventory Topology Model
                               +------+---+------+
                               |     Network     |
                               |   Controller    |
                               +--------+--------+
                                        |
                  +---------------------+---------------------+
                  |                  Network                  |
                  +-------------------------------------------+

          Figure 1: An Example Usage of Network Inventory Topology

3.2.  "What-if" Scenarios

   [I-D.irtf-nmrg-network-digital-twin-arch] defines Network Digital
   Twin (NDT) as a virtual representation of the physical network.  Such
   representation is meant to be used to analyze, diagnose, emulate, and
   then manage the physical network based on data, models, and
   interfaces.

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   [I-D.ietf-nmop-simap-concept] defines Service and Infrastructure Maps
   (SIMAP) as an abstraction model that provides a unified view of both
   service and infrastructure information, enabling correlation between
   service requirements and underlying resource capabilities.

   Both architectures require accurate mapping between logical network
   topology and physical inventory as a foundational data layer.  This
   model provides the essential physical resource information to such
   systems, enabling them to perform accurate "what-if" analysis (e.g.,
   impact prediction of hardware EOL, path re-optimization under
   resource constraints, service availability assessment).

4.  Module Tree Structure

   An overview of the structure of the "ietf-network-inventory-topology"
   module is shown in Figure 2.

      module: ietf-network-inventory-topology
        augment /nw:networks/nw:network/nw:node:
          +--rw inventory-mapping-attributes
             +--rw ne-ref?   nwi:ne-ref
        augment /nw:networks/nw:network/nt:link:
          +--rw inventory-mapping-attributes
             +--rw link-type?   string
        augment /nw:networks/nw:network/nw:node/nt:termination-point:
          +--rw inventory-mapping-attributes
             +--rw ne-ref?          nwi:ne-ref
             +--rw port-ref?        leafref
             +--ro port-breakout!
                +--ro breakout-channel* [channel-id]
                   +--ro channel-id    uint16

    Figure 2: The Structure of the Network Inventory Mapping Data Model

   The module defines two features "inventory-to-topology-navigate" and
   "topology-to-inventory-navigate" to control the navigation direction
   (from topology to inventory and vice versa).

   The module augments the "ietf-network-topology" module as follows:

   *  Inventory mapping attributes for nodes, links, and termination
      points: The corresponding containers augments the topology module
      with the references to the base network inventory

      The inventory topology model associates inventory data with
      overlay topologies.  It can be used as the "supporting-networks"
      of SAP, Layer 2, or Layer 3 topologies.

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4.1.  Link Extensions

   This document adds a lightweight "link-type" leaf to the topology
   link mapping to enable basic physical media classification.

   *  "link-type" – A string indicating the link media type, such as
      "copper", "fiber", or "coax".  For wireless media, values such as
      "microwave", or "wifi" may be used

   The "link-type" serves as a lightweight discriminator that guides to
   the appropriate specialized inventory model for detailed resource
   information.  For example, wired media (fiber, copper) typically
   reference a passive network inventory model, such as the one defined
   in [I-D.ygb-ivy-passive-network-inventory].

4.2.  Port-Breakout Capability

   High-density Ethernet ports (e.g., 400 Gb/s DR4) can be split into
   multiple independent lower-speed channels.  The breakout channels
   represent the intrinsic capability of the port to be partitioned,
   regardless of whether the port is currently configured as a trunk or
   as a breakout port.

   A trunk port is associated with exactly one physical interface.  A
   breakout port is a port that is decomposed into two or more physical
   interfaces; those interfaces may run at the same or different speeds
   and may consume the same or a different number of breakout channels.

   The container "port-breakout" is added under the termination-point
   augmentation.  It lists the logical channels into which the single
   physical port can be divided.  Only termination-points whose parent
   port is breakout-capable need to instantiate the container; otherwise
   the container is omitted, keeping the topology model minimal for the
   common non-breakout case.

   Breakout channel is an atomic resource element obtained by
   partitioning a breakout port.  One physical interface may be
   associated with one or more breakout channels, but one breakout
   channel MUST NOT be associated with more than one physical interface.
   Appendix B provides example configurations.

   It is assumed that a port which supports breakout can be configured
   either as a trunk port or as a breakout port.  Interface
   channelisation (e.g., VLAN sub-interfaces) is outside the scope of
   this document and is addressed by the Layer 2 network topology model
   [RFC8944].

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5.  Network Inventory Topology YANG Module

   This module augments the Network Topology [RFC8345].

   This module imports the base network inventory
   [I-D.ietf-ivy-network-inventory-yang].

   <CODE BEGINS> file "ietf-network-inventory-topology@2026-02-28.yang"
   module ietf-network-inventory-topology {
     yang-version 1.1;
     namespace
       "urn:ietf:params:xml:ns:yang:ietf-network-inventory-topology";
     prefix nwit;

     import ietf-network {
       prefix nw;
       reference
         "RFC 8345: A YANG Data Model for Network Topologies,
                    Section 4.1";
     }
     import ietf-network-topology {
       prefix nt;
       reference
         "RFC 8345: A YANG Data Model for Network Topologies,
                    Section 4.2";
     }
     import ietf-network-inventory {
       prefix nwi;
       reference
         "RFC AAAA: A YANG Data Model for Network Inventory";
     }

     organization
       "IETF Network Inventory YANG (ivy) Working Group";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/ivy>
        WG List:  IVY <mailto:inventory-yang@ietf.org>

        Editor: Bo Wu
                <lana.wubo@huawei.com>
        Editor: Mohamed Boucadair
                <mohamed.boucadair@orange.com>
        Author: Cheng Zhou
                <zhouchengyjy@chinamobile.com>
        Author: Qin Wu
                <bill.wu@huawei.com>";
     description
       "This YANG module defines a YANG module for network

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        topology and inventory mapping.

        Copyright (c) 2026 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).

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

     revision 2026-02-28 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: A Network Data Model for Inventory Topology
                    Mapping";
     }

     // Groupings
     // Node Grouping with 1:1 mapping to NE

     grouping node-inventory-mapping-attributes {
       description
         "Attributes for mapping a topology node to a Network Element
          (NE) in the physical inventory.";
       container inventory-mapping-attributes {
         description
           "Container for inventory mapping attributes of a node.";
         leaf ne-ref {
           type nwi:ne-ref;
           description
             "Reference to the NE in the inventory that corresponds to
              this topology node.

              This reference establishes a 1:1 mapping between the
              logical node and its physical NE.";
         }
       }
     }

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     // TP Grouping with 1:1 mapping to physical port

     grouping tp-inventory-mapping-attributes {
       description
         "Attributes for mapping a topology termination point (TP)
          to a physical port in the network inventory.";
       container inventory-mapping-attributes {
         description
           "Container for inventory mapping attributes of a TP.";
         uses nwi:port-ref {
           refine "port-ref" {
             description
               "Reference to the physical port component in the
                network inventory. This reference establishes a 1:1
                mapping between the logical TP and its physical port
                component.";
           }
         }
         // breakout channels (lightweight, per physical port)
         container port-breakout {
           presence "Indicates the port supports channel breakout.";
           config false;
           description
             "Breakout capability of the physical port represented by
              this TP. One TP maps to one physical port; channels are
              listed here. This container is present only when the
              underlying hardware supports partitioning the port into
              multiple independent channels (e.g., 400G to 4x100G).";
           list breakout-channel {
             key "channel-id";
             description
               "List of breakout channels available on this port.
                Each entry represents an independent lane or sub-port
                that can be used for channelized interfaces.";
             leaf channel-id {
               type uint16;
               description
                 "Unique identifier for the breakout channel within the
                  scope of the parent port.";
             }
           } // breakout-channel
         } // port-breakout
       }
     }

     // Link Grouping  with placeholder for future augumentation

     grouping link-inventory-mapping-attributes {

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       description
         "Attributes for classifying link media type.
          Detailed inventory reference is intentionally omitted from
          this model; implementations should use the appropriate
          specialized inventory modules based on the indicated
          link-type.";
       container inventory-mapping-attributes {
         description
           "Container for inventory-related attributes of a link.

            This container provides lightweight media classification.
            The link-type indicates which specialized inventory model
            contains detailed resource information:

            - Wired media (fiber, copper): passive network inventory
            - Wireless media (microwave, Wi-Fi): wireless-specific
              inventory

              Detailed inventory references may be added in future
              modules.";
         leaf link-type {
           type string;
           description
             "Classification of the link media type at the topology
              layer. Example values include 'copper', 'fiber',
              'microwave', or 'wifi'.";
         }
       }
     }

     // Main blocks

     augment "/nw:networks/nw:network/nw:node" {
       description
         "Augments the network topology node with inventory mapping
          attributes. This enables correlation between the logical node
          and its physical network element.";
       uses node-inventory-mapping-attributes;
     }

     augment "/nw:networks/nw:network/nt:link" {
       description
         "Augments the network topology link with inventory-related
          attributes.";
       uses link-inventory-mapping-attributes;
     }

     augment "/nw:networks/nw:network/nw:node/nt:termination-point" {

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       description
         "Augments the TP with inventory mapping attributes for
          physical port correlation and breakout capability reporting.";
       uses tp-inventory-mapping-attributes;
     }
   }
   <CODE ENDS>

6.  Operational Considerations

   This model enables a network controller to report discovered network
   topology and inventory information.  Automatic discovery serves as
   the primary mechanism, with selective configuration capabilities
   provided for scenarios where discovery is not feasible.

   For typical operations such as service provisioning and network
   planning, the model offers read-only query access to authoritative
   mappings between logical topology and physical inventory.  The
   inventory-mapping-attributes containers are defined as read-write
   (config true) to accommodate cases where automatic discovery is not
   possible, including:

   *  Customer-premises equipment (CPE) outside the operator's
      management domain

   *  Leased lines and third-party transport resources

   *  Planned or hypothetical resources for future deployment

   In these cases, the operator manually configures the mapping to
   maintain accurate topology-to-inventory correlation.

   The following nodes are read-only (config false) as they represent
   hardware-determined state:

   port-breakout: Hardware capability determined by physical port
   characteristics

7.  Security Considerations

   This section is modeled after the template described in Section 3.7
   of [I-D.ietf-netmod-rfc8407bis].

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   The "ietf-network-inventory-topology" YANG module defines a data
   model that is designed to be accessed via YANG-based management
   protocols, such as NETCONF [RFC6241] and RESTCONF [RFC8040].  These
   YANG-based management (1) have to use a secure transport layer (e.g.,
   SSH [RFC4252], TLS [RFC8446], and QUIC {{?RFC9000]) and (2) 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 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:

   'ne-ref', 'port-ref', 'link-type': These nodes are sensitive as they
   establish the mapping between logical topology and physical
   inventory.  Unauthorized modification could lead to incorrect
   resource allocation or service disruption.

   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:

   'ne-ref': The references may be used to track the set of network
   elements.  While read-only, they may reveal network infrastructure
   details.

   'port-breakout': This node exposes hardware capabilities.

8.  IANA Considerations

   IANA is requested to register the following URI in the "ns"
   subregistry within the "IETF XML Registry" [RFC3688]:

      URI:  urn:ietf:params:xml:ns:yang:ietf-network-inventory-topology
      Registrant Contact:  The IESG.
      XML:  N/A; the requested URI is an XML namespace.

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   IANA is requested to register the following YANG module in the "YANG
   Module Names" registry [RFC6020] within the "YANG Parameters"
   registry group:

   Name:  ietf-network-inventory-topology
   Namespace:  urn:ietf:params:xml:ns:yang:ietf-network-inventory-topology
   Prefix:  nwit
   Maintained by IANA?  N
   Reference:  RFC XXXX

9.  References

9.1.  Normative References

   [I-D.ietf-ivy-network-inventory-yang]
              Yu, C., Belotti, S., Bouquier, J., Peruzzini, F., and P.
              Bedard, "A Base YANG Data Model for Network Inventory",
              Work in Progress, Internet-Draft, draft-ietf-ivy-network-
              inventory-yang-14, 5 February 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-ivy-
              network-inventory-yang-14>.

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

   [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/rfc/rfc6020>.

   [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/rfc/rfc8341>.

   [RFC8345]  Clemm, A., Medved, J., Varga, R., Bahadur, N.,
              Ananthakrishnan, H., and X. Liu, "A YANG Data Model for
              Network Topologies", RFC 8345, DOI 10.17487/RFC8345, March
              2018, <https://www.rfc-editor.org/rfc/rfc8345>.

   [RFC9408]  Boucadair, M., Ed., Gonzalez de Dios, O., Barguil, S., Wu,
              Q., and V. Lopez, "A YANG Network Data Model for Service
              Attachment Points (SAPs)", RFC 9408, DOI 10.17487/RFC9408,
              June 2023, <https://www.rfc-editor.org/rfc/rfc9408>.

9.2.  Informative References

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   [I-D.ietf-ivy-network-inventory-software]
              Wu, B., Zhou, C., Wu, Q., and M. Boucadair, "A YANG
              Network Data Model of Network Inventory Software
              Extensions", Work in Progress, Internet-Draft, draft-ietf-
              ivy-network-inventory-software-02, 20 October 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-ivy-
              network-inventory-software-02>.

   [I-D.ietf-netmod-rfc8407bis]
              Bierman, A., Boucadair, M., and Q. Wu, "Guidelines for
              Authors and Reviewers of Documents Containing YANG Data
              Models", Work in Progress, Internet-Draft, draft-ietf-
              netmod-rfc8407bis-28, 5 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              rfc8407bis-28>.

   [I-D.ietf-nmop-simap-concept]
              Havel, O., Claise, B., de Dios, O. G., and T. Graf,
              "SIMAP: Concept, Requirements, and Use Cases", Work in
              Progress, Internet-Draft, draft-ietf-nmop-simap-concept-
              08, 23 February 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-nmop-
              simap-concept-08>.

   [I-D.irtf-nmrg-network-digital-twin-arch]
              Zhou, C., Yang, H., Duan, X., Lopez, D., Pastor, A., Wu,
              Q., Boucadair, M., and C. Jacquenet, "Network Digital
              Twin: Concepts and Reference Architecture", Work in
              Progress, Internet-Draft, draft-irtf-nmrg-network-digital-
              twin-arch-12, 27 February 2026,
              <https://datatracker.ietf.org/doc/html/draft-irtf-nmrg-
              network-digital-twin-arch-12>.

   [I-D.ygb-ivy-passive-network-inventory]
              Yu, C., Guo, A., Busi, I., Boroon, M., Belotti, S., van
              caenegem, T., S., S. 1., B., S., Davis, N., Tilocca, M.,
              Peters, B., Yoon, B. Y., LIUYUCONG, Zhao, Y., and A.
              Sakalabhaktula, "A YANG Data Model for Passive Network
              Inventory", Work in Progress, Internet-Draft, draft-ygb-
              ivy-passive-network-inventory-03, 7 January 2026,
              <https://datatracker.ietf.org/doc/html/draft-ygb-ivy-
              passive-network-inventory-03>.

   [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/rfc/rfc4252>.

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   [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/rfc/rfc6241>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/rfc/rfc7951>.

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

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/rfc/rfc8340>.

   [RFC8346]  Clemm, A., Medved, J., Varga, R., Liu, X.,
              Ananthakrishnan, H., and N. Bahadur, "A YANG Data Model
              for Layer 3 Topologies", RFC 8346, DOI 10.17487/RFC8346,
              March 2018, <https://www.rfc-editor.org/rfc/rfc8346>.

   [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/rfc/rfc8446>.

   [RFC8944]  Dong, J., Wei, X., Wu, Q., Boucadair, M., and A. Liu, "A
              YANG Data Model for Layer 2 Network Topologies", RFC 8944,
              DOI 10.17487/RFC8944, November 2020,
              <https://www.rfc-editor.org/rfc/rfc8944>.

Appendix A.  "link-type" Usage Examples

   This appendix provides examples illustrating the usage of the link-
   type data node.

   Scenario: Device SW-1 and device SW-2 are directly connected by a
   fiber.

   Physical topology:

   +--------+                                    +--------+
   |        |                                    |        |
   | [SW-1] +========= fiber link ===============+ [SW-2] |
   |        |                                    |        |
   +--------+                                    +--------+

   Key parts of the JSON example is as follows:

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{
  "ietf-network:networks": {
    "network": [
      {
        "network-id": "campus-topology",
        "node": [
          {
            "node-id": "SW-1",
            "ietf-network-inventory-topology:inventory-mapping-attributes": {
              "ne-ref": "NE-SW1"
            },
            "ietf-network-topology:termination-point": [
              {
                "tp-id": "TP-SW1-P1",
                "ietf-network-inventory-topology:inventory-mapping-attributes": {
                  "ne-ref": "NE-SW1",
                  "port-ref": "/nwi:network-inventory/nwi:network-elements/nwi:network-element[ne-id='NE-SW1']/nwi:components/nwi:component[component-id='eth-port-1']"
                }
              }
            ]
          },
          {
            "node-id": "SW-2",
            "ietf-network-inventory-topology:inventory-mapping-attributes": {
              "ne-ref": "NE-SW2"
            },
            "ietf-network-topology:termination-point": [
              {
                "tp-id": "TP-SW2-P1",
                "ietf-network-inventory-topology:inventory-mapping-attributes": {
                  "ne-ref": "NE-SW2",
                  "port-ref": "/nwi:network-inventory/nwi:network-elements/nwi:network-element[ne-id='NE-SW2']/nwi:components/nwi:component[component-id='eth-port-1']"
                }
              }
            ]
          }
        ],
        "ietf-network-topology:link": [
          {
            "link-id": "Link-SW1-SW2",
            "source": {
              "source-node": "SW-1",
              "source-tp": "TP-SW1-P1"
            },
            "destination": {
              "dest-node": "SW-2",
              "dest-tp": "TP-SW2-P1"
            },

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            "ietf-network-inventory-topology:inventory-mapping-attributes": {
              "link-type": "fiber"
            }
          }
        ]
      }
    ]
  }
}

Appendix B.  JSON Example of an MPO Breakout-Channel Port

   This appendix provides an example of a 400 Gb/s DR4 port that is
   physically implemented as four independent 100 Gb/s lanes (an MPO
   breakout).  The lanes are exposed as breakout-channel entries so that
   the port can later be configured as either a single 400G trunk or
   four 100G breakout interfaces.  The instance data below shows the
   minimal JSON encoding [RFC7951] of the "port-breakout" container for
   this port.

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   =============== NOTE: '\' line wrapping per RFC 8792 ================

   {
     "ietf-network-topology:networks": {
       "network": [
         {
           "network-id": "example:underlay-topology-400g",
           "node": [
             {
               "node-id": "example:n1",
               "termination-point": [
                 {
                   "tp-id": "example:400g-1/0/1",
                   "ietf-network-inventory-topology:inventory-mapping-\
                                                          attributes": {
                     "ne-ref": "example:NE-1",
                     "port-ref": "example:port-1",
                     "port-breakout": {
                       "breakout-channel": [
                         { "channel-id": 1 },
                         { "channel-id": 2 },
                         { "channel-id": 3 },
                         { "channel-id": 4 }
                       ]
                     }
                   }
                 }
               ]
             }
           ]
         }
       ]
     }
   }

Acknowledgments

   The authors wish to thank Italo Busi, Olga Havel, Aihua Guo, Oscar
   Gonzalez de Dios, and many others for their helpful comments and
   suggestions.

Contributors

   Chaode Yu
   Huawei
   Email: yuchaode@huawei.com

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Authors' Addresses

   Bo Wu (editor)
   Huawei
   Email: lana.wubo@huawei.com

   Mohamed Boucadair
   Orange
   Email: mohamed.boucadair@orange.com

   Cheng Zhou
   China Mobile
   Email: zhouchengyjy@chinamobile.com

   Qin Wu
   Huawei
   Email: bill.wu@huawei.com

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