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Network Working Group                                           A. Clemm
Internet-Draft                                                    Huawei
Intended status: Standards Track                               J. Medved
Expires: March 23, 2018                                            Cisco
                                                                R. Varga
                                               Pantheon Technologies SRO
                                                                  X. Liu
                                                                Ericsson
                                                      H. Ananthakrishnan
                                                           Packet Design
                                                              N. Bahadur
                                                       Bracket Computing
                                                      September 19, 2017


                A YANG Data Model for Layer 3 Topologies
                draft-ietf-i2rs-yang-l3-topology-11.txt

Abstract

   This document defines a YANG data model for layer 3 network
   topologies.

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 March 23, 2018.

Copyright Notice

   Copyright (c) 2017 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



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   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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Key Words . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Definitions and Acronyms  . . . . . . . . . . . . . . . . . .   3
   4.  Model Structure . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Layer 3 Unicast Topology Model Overview . . . . . . . . . . .   5
   6.  Layer 3 Unicast Topology YANG Module  . . . . . . . . . . . .   7
   7.  Interactions with Other YANG Modules  . . . . . . . . . . . .  15
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  17
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     12.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Appendix A.  Companion YANG model for non-NMDA compliant
                implementations  . . . . . . . . . . . . . . . . . .  20
   Appendix B.  Extending the Model  . . . . . . . . . . . . . . . .  24
     B.1.  Example OSPF Topology . . . . . . . . . . . . . . . . . .  24
       B.1.1.  Model Overview  . . . . . . . . . . . . . . . . . . .  24
       B.1.2.  OSPF Topology YANG Module . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Introduction

   This document introduces a YANG [RFC7950] [RFC6991] data model for
   Layer 3 network topologies, specifically Layer 3 Unicast.  The model
   allows an application to have a holistic view of the topology of a
   Layer 3 network, all contained in a single conceptual YANG datastore.
   The data model builds on top of, and augments, the data model for
   network topologies defined in
   [I-D.draft-ietf-i2rs-yang-network-topo].

   This document also shows how the model can be further refined to
   cover different Layer 3 Unicast topology types.  For this purpose,
   example model is introduced that covers OSPF [RFC2328].  This example
   is intended purely for illustrative purpose; we expect that full-
   blown OSPF model will be more comprehensive and refined than the
   example shown here.




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   There are multiple applications for a topology data model.  A number
   of use cases have been defined in section 6 of
   [I-D.draft-ietf-i2rs-usecase-reqs-summary].  For example, nodes
   within the network can use the data model to capture their
   understanding of the overall network topology and expose it to a
   network controller.  A network controller can then use the
   instantiated topology data to compare and reconcile its own view of
   the network topology with that of the network elements that it
   controls.  Alternatively, nodes within the network could propagate
   this understanding to compare and reconcile this understanding either
   amongst themselves or with help of a controller.  Beyond the network
   element itself, a network controller might even use the data model to
   represent its view of the topology that it controls and expose it to
   applications north of itself.

   The data model for Layer 3 Unicast topologies defined in this
   document is specified in a YANG module "ietf-l3-unicast-topology".
   To do so, it augments general network topology model defined in
   [I-D.draft-ietf-i2rs-yang-network-topo] with information specific to
   Layer 3 Unicast.  This way, the general topology model is extended to
   be able to meet the needs of Layer 3 Unicast topologies.

   Information that is kept in the Traffic Engineering Database (TED)
   will be specified in a separate model
   [I-D.draft-ietf-teas-yang-te-topo] and outside the scope of this
   specification.

2.  Key Words

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Definitions and Acronyms

   As this document defines a YANG data model, in this document many
   terms are used that have been defined in conjunction with YANG
   [RFC7950] and NETCONF [RFC6241].  Some terms, such as datastore and
   data tree, are repeated here for clarity and to put them in context.

   Datastore: A conceptual store of instantiated management information,
   with individual data items represented by data nodes which are
   arranged in hierarchical manner.

   Data subtree: An instantiated data node and the data nodes that are
   hierarchically contained within it.



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   HTTP: Hyper-Text Transfer Protocol

   IGP: Interior Gateway Protocol

   IS-IS: Intermediate System to Intermediate System protocol

   LSP: Label Switched Path

   NETCONF: Network Configuration Protocol

   NMDA: Network Management Datastore Architecture

   OSPF: Open Shortest Path First, a link state routing protocol

   URI: Uniform Resource Identifier

   ReST: Representational State Transfer, a style of stateless interface
   and protocol that is generally carried over HTTP

   SRLG: Shared Risk Link Group

   TED: Traffic Engineering Database

   YANG: A data definition language for NETCONF

4.  Model Structure

   The Layer 3 Unicast topology model is defined by YANG module "l3-
   unicast-topology".  The relationship of this module with other YANG
   modules is roughly depicted in the figure below.





















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           +-----------------------------+
           |  +-----------------------+  |
           |  |      ietf-network     |  |
           |  +----------^------------+  |
           |             |               |
           |  +-----------------------+  |
           |  | ietf-network-topology |  |
           |  +----------+------------+  |
           +-------------^---------------+
                         |
                         |
             +-----------^-------------+
             |   L3-UNICAST-TOPOLOGY   |
             +----+------^--------+----+
                         |
                         |
                 +-------^-------+
                 | ospf-topology |
                 +---------------+

                     Figure 1: Overall model structure

   YANG modules "ietf-network" and "ietf-network-topology" collectively
   define the basic network topology model.  YANG module "ietf-l3-
   unicast-topology" augments those models with additional definitions
   needed to represent Layer 3 Unicast topologies.  This module in turn
   can be augmented by YANG modules with additional definitions for
   specific types of Layer 3 Unicast topologies, such as OSPF and for
   IS-IS topologies.

   The YANG modules ietf-network and ietf-network are designed to be
   used in conjunction with implementations that support the Network
   Management Datastore Architecture (NMDA) defined in
   [I-D.draft-ietf-netmod-revised-datastores].  Accordingly, the same is
   true for the YANG modules that augment it.  In order to allow
   implementations to use the model even in cases when NMDA is not
   supported, companion YANG modules (that SHOULD NOT be supported by
   implementations that support NMDA) are defined in an Appendix, see
   Appendix A.

5.  Layer 3 Unicast Topology Model Overview

   The Layer 3 Unicast topology model is defined by YANG module "ietf-
   l3-unicast-topology".  Its structure is depicted in the following
   diagram.  The notation syntax follows
   [I-D.draft-ietf-netmod-yang-tree-diagrams].  For purposes of brevity,
   notifications are not depicted.




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   module: ietf-l3-unicast-topology
     augment /nd:networks/nd:network/nd:network-types:
       +--rw l3-unicast-topology!
     augment /nd:networks/nd:network:
       +--rw l3-topology-attributes
          +--rw name?   string
          +--rw flag*   l3-flag-type
     augment /nd:networks/nd:network/nd:node:
       +--rw l3-node-attributes
          +--rw name?        inet:domain-name
          +--rw flag*        node-flag-type
          +--rw router-id*   inet:ip-address
          +--rw prefix* [prefix]
             +--rw prefix    inet:ip-prefix
             +--rw metric?   uint32
             +--rw flag*     prefix-flag-type
     augment /nd:networks/nd:network/lnk:link:
       +--rw l3-link-attributes
          +--rw name?      string
          +--rw flag*      link-flag-type
          +--rw metric1?   uint64
          +--rw metric2?   uint64
     augment /nd:networks/nd:network/nd:node/lnk:termination-point:
       +--rw l3-termination-point-attributes
          +--rw (termination-point-type)?
             +--:(ip)
             |  +--rw ip-address*       inet:ip-address
             +--:(unnumbered)
             |  +--rw unnumbered-id?    uint32
             +--:(interface-name)
                +--rw interface-name?   string

   The module augments the original ietf-network and ietf-network-
   topology modules as follows:

   o  A new network topology type is introduced, l3-unicast-topology.
      The corresponding container augments the network-types of the
      ietf-network module.

   o  Additional topology attributes are introduced, defined in a
      grouping, which augments the "network" list of the network module.
      The attributes include a name for the topology, as well as a set
      of flags (represented through a leaf-list).  Each type of flag is
      represented by a separate identity.  This allows to introduce
      additional flags in augmenting modules using additional identities
      without needing to revise this module.





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   o  Additional data objects for nodes are introduced by augmenting the
      "node" list of the network module.  New objects include again a
      set of flags, as well as a list of prefixes.  Each prefix in turn
      includes an ip prefix, a metric, and a prefix-specific set of
      flags.

   o  Links (in the ietf-network-topology module) are augmented with a
      set of parameters as well, allowing to associate a link with a
      link name, another set of flags, and a link metric.

   o  Termination points (in the ietf-network-topology module as well)
      are augmented with a choice of IP address, identifier, or name.

   In addition, the module defines a set of notifications to alert
   clients of any events concerning links, nodes, prefixes, and
   termination points.  Each notification includes an indication of the
   type of event, the topology from which it originated, and the
   affected node, or link, or prefix, or termination point.  In
   addition, as a convenience to applications, additional data of the
   affected node, or link, or termination point (respectively) is
   included.  While this makes notifications larger in volume than they
   would need to be, it avoids the need for subsequent retrieval of
   context information, which also might have changed in the meantime.

6.  Layer 3 Unicast Topology YANG Module

   <CODE BEGINS> file "ietf-l3-unicast-topology@2017-09-19.yang"
   module ietf-l3-unicast-topology {
     yang-version 1.1;
     namespace
       "urn:ietf:params:xml:ns:yang:ietf-l3-unicast-topology";
     prefix "l3t";
     import ietf-network {
       prefix "nd";
     }
     import ietf-network-topology {
       prefix "lnk";
     }
     import ietf-inet-types {
       prefix "inet";
     }
     organization
       "IETF I2RS (Interface to the Routing System) Working Group";
     contact
       "WG Web:    <http://tools.ietf.org/wg/i2rs/>
        WG List:   <mailto:i2rs@ietf.org>
        Editor:    Alexander Clemm
                   <mailto:ludwig@clemm.org>



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        Editor:    Jan Medved
                   <mailto:jmedved@cisco.com>
        Editor:    Robert Varga
                   <mailto:robert.varga@pantheon.sk>
        Editor:    Xufeng Liu
                   <mailto:xliu@kuatrotech.com>
        Editor:    Nitin Bahadur
                   <mailto:nitin_bahadur@yahoo.com>
        Editor:    Hariharan Ananthakrishnan
                   <mailto:hari@packetdesign.com>";
     description
       "This module defines a model for Layer 3 Unicast
        topologies.
        Copyright (c) 2017 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 Simplified 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
        draft-ietf-i2rs-yang-l3-topology-11;
        see the RFC itself for full legal notices.
        NOTE TO RFC EDITOR: Please replace above reference to
        draft-ietf-i2rs-yang-l3-topology-11 with RFC
        number when published (i.e. RFC xxxx).";
     revision "2017-09-19" {
       description
         "Initial revision.
          NOTE TO RFC EDITOR: Please replace the following reference
          to draft-ietf-i2rs-yang-l3-topology-11 with
          RFC number when published (i.e. RFC xxxx).";
       reference
         "draft-ietf-i2rs-yang-l3-topology-11";
     }

     identity flag-identity {
       description "Base type for flags";
     }

     typedef l3-event-type {
       type enumeration {
         enum "add" {
           description
             "An Layer 3 node or link or prefix or termination-point has
             been added";
         }



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         enum "remove" {
           description
             "An Layer 3 node or link or prefix or termination-point has
             been removed";
         }
         enum "update" {
           description
             "An Layer 3 node or link or prefix or termination-point has
             been updated";
         }
       }
       description "Layer 3 Event type for notifications";
     }

     typedef prefix-flag-type {
       type identityref {
         base "flag-identity";
       }
       description "Prefix flag attributes";
     }

     typedef node-flag-type {
       type identityref {
         base "flag-identity";
       }
       description "Node flag attributes";
     }

     typedef link-flag-type {
       type identityref {
         base "flag-identity";
       }
       description "Link flag attributes";
     }

     typedef l3-flag-type {
       type identityref {
         base "flag-identity";
       }
       description "L3 flag attributes";
     }

     grouping l3-prefix-attributes {
       description
         "L3 prefix attributes";
       leaf prefix {
         type inet:ip-prefix;
         description



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           "IP prefix value";
       }
       leaf metric {
         type uint32;
         description
           "Prefix metric";
       }
       leaf-list flag {
         type prefix-flag-type;
         description
           "Prefix flags";
       }
     }
     grouping l3-unicast-topology-type {
       description "Identify the topology type to be L3 unicast.";
       container l3-unicast-topology {
         presence "indicates L3 Unicast Topology";
         description
           "The presence of the container node indicates L3 Unicast
           Topology";
       }
     }
     grouping l3-topology-attributes {
       description "Topology scope attributes";
       container l3-topology-attributes {
         description "Containing topology attributes";
         leaf name {
           type string;
           description
             "Name of the topology";
         }
         leaf-list flag {
           type l3-flag-type;
           description
             "Topology flags";
         }
       }
     }
     grouping l3-node-attributes {
       description "L3 node scope attributes";
       container l3-node-attributes {
         description
           "Containing node attributes";
         leaf name {
           type inet:domain-name;
           description
             "Node name";
         }



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         leaf-list flag {
           type node-flag-type;
           description
             "Node flags";
         }
         leaf-list router-id {
           type inet:ip-address;
           description
             "Router-id for the node";
         }
         list prefix {
           key "prefix";
           description
             "A list of prefixes along with their attributes";
           uses l3-prefix-attributes;
         }
       }
     }
     grouping l3-link-attributes {
       description
         "L3 link scope attributes";
       container l3-link-attributes {
         description
           "Containing link attributes";
         leaf name {
           type string;
           description
             "Link Name";
         }
         leaf-list flag {
           type link-flag-type;
           description
             "Link flags";
         }
         leaf metric1 {
           type uint64;
           description
               "Link Metric 1";
         }
         leaf metric2 {
           type uint64;
           description
               "Link Metric 2";
         }
       }
     }
     grouping l3-termination-point-attributes {
       description "L3 termination point scope attributes";



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       container l3-termination-point-attributes {
         description
           "Containing termination point attributes";
         choice termination-point-type {
           description
             "Indicates the termination point type";
           case ip {
             leaf-list ip-address {
               type inet:ip-address;
               description
                 "IPv4 or IPv6 address.";
             }
           }
           case unnumbered {
             leaf unnumbered-id {
               type uint32;
               description
                 "Unnumbered interface identifier.
                  The identifier will correspond to the ifIndex value
                  of the interface, i.e. the ifIndex value of the
                  ifEntry that represents the interface in
                  implementations where the Interfaces Group MIB
                  (RFC 2863) is supported.";
               reference
                 "RFC 2863: The Interfaces Group MIB";
             }
           }
           case interface-name {
             leaf interface-name {
               type string;
               description
                 "A name of the interface.  The name can (but does not
                  have to) correspond to an interface reference of a
                  containing node's interface, i.e. the path name of a
                  corresponding interface data node on the containing
                  node reminiscent of data type if-ref defined in
                  RFC 7223. It should be noted that data type if-ref of
                  RFC 7223 cannot be used directly, as this data type
                  is used to reference an interface in a datastore of
                  a single node in the network, not to uniquely
                  reference interfaces across a network.";
             }
           }
         }
       }
     }
     augment "/nd:networks/nd:network/nd:network-types" {
       description



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         "Introduce new network type for L3 unicast topology";
       uses l3-unicast-topology-type;
     }
     augment "/nd:networks/nd:network" {
       when "nd:network-types/l3-unicast-topology" {
         description
           "Augmentation parameters apply only for networks with
           L3 unicast topology";
       }
       description
           "L3 unicast for the network as a whole";
       uses l3-topology-attributes;
     }
     augment "/nd:networks/nd:network/nd:node" {
       when "../nd:network-types/l3-unicast-topology" {
         description
           "Augmentation parameters apply only for networks with
           L3 unicast topology";
       }
       description
           "L3 unicast node level attributes ";
       uses l3-node-attributes;
     }
     augment "/nd:networks/nd:network/lnk:link" {
       when "../nd:network-types/l3-unicast-topology" {
         description
           "Augmentation parameters apply only for networks with
           L3 unicast topology";
       }
       description
         "Augment topology link attributes";
       uses l3-link-attributes;
     }
     augment "/nd:networks/nd:network/nd:node/"
            +"lnk:termination-point" {
       when "../../nd:network-types/l3-unicast-topology" {
         description
           "Augmentation parameters apply only for networks with
           L3 unicast topology";
       }
       description "Augment topology termination point configuration";
       uses l3-termination-point-attributes;
     }
     notification l3-node-event {
       description
         "Notification event for L3 node";
       leaf l3-event-type {
         type l3-event-type;



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         description
           "Event type";
       }
       uses nd:node-ref;
       uses l3-unicast-topology-type;
       uses l3-node-attributes;
     }
     notification l3-link-event {
       description
         "Notification event for L3 link";
       leaf l3-event-type {
         type l3-event-type;
         description
           "Event type";
       }
       uses lnk:link-ref;
       uses l3-unicast-topology-type;
       uses l3-link-attributes;
     }
     notification l3-prefix-event {
       description
         "Notification event for L3 prefix";
       leaf l3-event-type {
         type l3-event-type;
         description
           "Event type";
       }
       uses nd:node-ref;
       uses l3-unicast-topology-type;
       container prefix {
         description
           "Containing L3 prefix attributes";
         uses l3-prefix-attributes;
       }
     }
     notification termination-point-event {
       description
         "Notification event for L3 termination point";
       leaf l3-event-type {
         type l3-event-type;
         description
           "Event type";
       }
       uses lnk:tp-ref;
       uses l3-unicast-topology-type;
       uses l3-termination-point-attributes;
     }
   }



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   <CODE ENDS>

7.  Interactions with Other YANG Modules

   As described in section Section 4, the model builds on top of, and
   augments, the YANG modules defined in
   [I-D.draft-ietf-i2rs-yang-network-topo].  Specifically, module ietf-
   l3-unicast-topology augments modules "ietf-network" and "ietf-
   network-topology".  In addition, the model makes use of data types
   that have been defined in [RFC6991].

   The moodel defines a protocol independent YANG data model with layer
   3 topology information.  It is separate from and not linked with data
   models that are used to configure routing protocols or routing
   information.  This includes e.g. model "ietf-routing" [RFC8022] and
   model "ietf-fb-rib" [I-D.draft-acee-rtgwg-yang-rib-extend].

   The model obeys the requirements for the ephemeral state found in the
   document [I-D.draft-ietf-i2rs-ephemeral-state].  For ephemeral
   topology data that is server provided, the process tasked with
   maintaining topology information will load information from the
   routing process (such as OSPF) into the data model without relying on
   a configuration datastore.

8.  IANA Considerations

   This document registers the following namespace URIs in the "IETF XML
   Registry" [RFC3688]:

   URI: urn:ietf:params:xml:ns:yang:ietf-l3-unicast-topology
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.

   URI: urn:ietf:params:xml:ns:yang:ietf-l3-unicast-topology-state
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.

   This document registers the following YANG modules in the "YANG
   Module Names" registry [RFC6020]:

   Name: ietf-l3-unicast-topology
   Namespace: urn:ietf:params:xml:ns:yang:ietf-l3-unicast-topology
   Prefix: l3t
   Reference: draft-ietf-i2rs-yang-l3-topology-11.txt (RFC form)

   Name: ietf-l3-unicast-topology-state
   Namespace: urn:ietf:params:xml:ns:yang:ietf-l3-unicast-topology-state
   Prefix: l3t-s



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   Reference: draft-ietf-i2rs-yang-l3-topology-11.txt (RFC form)

9.  Security Considerations

   The YANG module defined in this document is designed to be accessed
   via network management protocols such as NETCONF [RFC6241] or
   RESTCONF [RFC8040].  The lowest NETCONF layer is the secure transport
   layer, and the mandatory-to-implement secure transport is Secure
   Shell (SSH) [RFC6242].  The lowest RESTCONF layer is HTTPS, and the
   mandatory-to-implement secure transport is TLS [RFC5246].

   The NETCONF access control model [RFC6536] 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.

   In general, Layer 3 Unicast topologies are system-controlled and
   provide ephemeral topology information.  In an NMDA-complient server,
   they are only part of <operational> which provides read-only access
   to clients, they are less vulnerable.  That said, the YANG module
   does in principle allow information to be configurable.

   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).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  These are the subtrees and data nodes
   and their sensitivity/vulnerability in the ietf-network module:

      l3-topology-attributes: A malicious client could attempt to
      sabotage the configuration of any of the ctonained attributes,
      i.e. the name or the flag data nodes.

      l3-node-attributes: A malicious client could attempt to sabotage
      the configuration of important node attributes, such as the
      router-id or node prefix.

      l3-link-attributes: A malicious client could attempt to sabotage
      the configuration of important link attributes, such as name,
      flag, and metrics of the link respectively corresponding data
      nodes.

      l3-termination-point-attributes: A malicious client could attempt
      to sabotage the configuration information of a termination point,
      such as its ip-address and interface name, respectively the
      corresponding data nodes.




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10.  Contributors

   The model presented in this document was contributed to by more
   people than can be listed on the author list.  Additional
   contributors include:

   o  Vishnu Pavan Beeram, Juniper

   o  Igor Bryskin, Huawei

   o  Ken Gray, Cisco

   o  Aihua Guo, Huawei

   o  Tom Nadeau, Brocade

   o  Tony Tkacik

   o  Aleksandr Zhdankin, Cisco

11.  Acknowledgements

   We wish to acknowledge the helpful contributions, comments, and
   suggestions that were received from Alia Atlas, Andy Bierman, Benoit
   Claise, Joel Halpern, Susan Hares, Ladislav Lhotka, Carl Moberg,
   Carlos Pignataro, Juergen Schoenwaelder, and Kent Watsen.

12.  References

12.1.  Normative References

   [I-D.draft-ietf-i2rs-yang-network-topo]
              Clemm, A., Medved, J., Varga, R., Bahadur, N.,
              Ananthakrishnan, H., and X. Liu, "A YANG Data Model for
              Network Topologies", I-D draft-ietf-i2rs-yang-network-
              topo-16, September 2017.

   [I-D.draft-ietf-netmod-revised-datastores]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "A Revised Conceptual Model for YANG
              Datastores", I-D draft-ietf-netmod-revised-datastores-02,
              May 2017.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and
              Dual Environments", RFC 1195, December 1990.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to indicate
              requirement levels", RFC 2119, March 1997.



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   [RFC2328]  Moy, J., "OSPF Version 2", RFC 2328, April 1998.

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, June 2000.

   [RFC3688]  Mealling, M., "The IETF XML Registry", RFC 3688, January
              2004.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)",
              RFC 6241, June 2011.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, June 2011.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536, March
              2012.

   [RFC6991]  Schoenwaelder, J., "Common YANG Data Types", RFC 6991,
              July 2013.

   [RFC7950]  Bjorklund, M., "The YANG 1.1 Data Modeling Language",
              RFC 7950, August 2016.

12.2.  Informative References

   [I-D.draft-acee-rtgwg-yang-rib-extend]
              Lindem, A. and Y. Qu, "YANG Data Model for RIB
              Extensions", I-D draft-acee-rtgwg-yang-rib-extend-02,
              October 2016.

   [I-D.draft-ietf-i2rs-ephemeral-state]
              Haas, J. and S. Hares, "I2RS Ephemeral State
              Requirements", I-D draft-ietf-i2rs-ephemeral-state-23,
              November 2016.

   [I-D.draft-ietf-i2rs-usecase-reqs-summary]
              Hares, S. and M. Chen, "Summary of I2RS Use Case
              Requirements", I-D draft-ietf-i2rs-usecase-reqs-summary-
              03, November 2016.



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   [I-D.draft-ietf-netmod-yang-tree-diagrams]
              Bjorklund, M. and L. Berger, "YANG Tree Diagrams", I-D
              draft-ietf-netmod-yang-tree-diagrams, June 2017.

   [I-D.draft-ietf-teas-yang-te-topo]
              Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
              O. Gonzalez De Dios, "YANG Data Model for TE Topologies",
              I-D draft-ietf-teas-yang-te-topo-09, June 2017.

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Routing Management",
              RFC 7223, May 2014.

   [RFC8022]  Lhotka, L. and A. Lindem, "A YANG Data Model for Routing
              Management", RFC 8022, November 2016.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, January 2017.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", RFC 8174, May 2017.































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Appendix A.  Companion YANG model for non-NMDA compliant implementations

   The YANG module ietf-l3-unicast-topology defined in this document
   augments two modules, ietf-network and ietf-network-topology, that
   are designed to be used in conjunction with implementations that
   support the Network Management Datastore Architecture (NMDA) defined
   in [I-D.draft-ietf-netmod-revised-datastores].  In order to allow
   implementations to use the model even in cases when NMDA is not
   supported, a set of companion modules have been defined that
   represent a state model of networks and network topologies, ietf-
   network-state and ietf-network-topology-state, respectively.

   In order to be able to use the model for layer 3 topologies defined
   in this in this document in conjunction with non-NMDA compliant
   implementations, a corresponding companion module needs to be
   introduced as well.  This companion module, ietf-l3-unicast-topology-
   state, mirrors ietf-l3-unicast-topology.  However, the module
   augments ietf-network-state and ietf-network-topology-state (instead
   of ietf-network and ietf-network-state) and all of its data nodes are
   non-configurable.

   Similar considerations apply for any modules that augment ietf-l3-
   unicast-topology, such as the example modules defined in see
   Appendix B, example-ietf-ospf-topology.  For non-NMDA compliant
   implementations, companion modules will need to be introduced that
   represent state information and are non-configurable, augmenting
   ietf-l3-unicast-topology-state instead of ietf-l3-unicast-topology.
   Because they served as examples only, companion modules for those
   examples are not given.

   Like ietf-network-state and ietf-network-topology-state, ietf-l3-
   unicast-topology SHOULD NOT be supported by implementations that
   support NMDA.  It is for this reason that the module is defined in
   the Appendix.

   The definition of the module follows below.  As the structure of the
   module mirrors that of its underlying module, the YANG tree is not
   depicted separately.

   <CODE BEGINS> file "ietf-l3-unicast-topology-state@2017-09-19.yang"
   module ietf-l3-unicast-topology-state {
     yang-version 1.1;
     namespace
       "urn:ietf:params:xml:ns:yang:ietf-l3-unicast-topology-state";
     prefix "l3t-s";
     import ietf-network-state {
       prefix "nd-s";
     }



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     import ietf-network-topology-state {
       prefix "lnk-s";
     }
     import ietf-l3-unicast-topology {
       prefix "l3t";
     }
     organization
       "IETF I2RS (Interface to the Routing System) Working Group";
     contact
       "WG Web:    <http://tools.ietf.org/wg/i2rs/>
        WG List:   <mailto:i2rs@ietf.org>
        Editor:    Alexander Clemm
                   <mailto:ludwig@clemm.org>
        Editor:    Jan Medved
                   <mailto:jmedved@cisco.com>
        Editor:    Robert Varga
                   <mailto:robert.varga@pantheon.sk>
        Editor:    Xufeng Liu
                   <mailto:xliu@kuatrotech.com>
        Editor:    Nitin Bahadur
                   <mailto:nitin_bahadur@yahoo.com>
        Editor:    Hariharan Ananthakrishnan
                   <mailto:hari@packetdesign.com>";
     description
       "This module defines a model for Layer 3 Unicast topology
        state, representing topology that is either learned, or topology
        that results from applying topology that has been configured per
        the ietf-l3-unicast-topology model, mirroring the corresponding
        data nodes in this model.

        The model mirrors ietf-l3-unicast-topology, but contains only
        read-only state data.  The model is not needed when the
        underlying implementation infrastructure supports the Network
        Management Datastore Architecture (NMDA).

        Copyright (c) 2017 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 Simplified 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
        draft-ietf-i2rs-yang-l3-topology-11;
        see the RFC itself for full legal notices.
        NOTE TO RFC EDITOR: Please replace above reference to
        draft-ietf-i2rs-yang-l3-topology-11 with RFC



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        number when published (i.e. RFC xxxx).";
     revision "2017-09-19" {
       description
         "Initial revision.
          NOTE TO RFC EDITOR: Please replace the following reference
          to draft-ietf-i2rs-yang-l3-topology-11 with
          RFC number when published (i.e. RFC xxxx).";
       reference
         "draft-ietf-i2rs-yang-l3-topology-11";
     }

     augment "/nd-s:networks/nd-s:network/nd-s:network-types" {
       description
         "Introduce new network type for L3 unicast topology";
       uses l3t:l3-unicast-topology-type;
     }
     augment "/nd-s:networks/nd-s:network" {
       when "nd-s:network-types/l3-unicast-topology" {
         description
           "Augmentation parameters apply only for networks with
           L3 unicast topology";
       }
       description
           "L3 unicast for the network as a whole";
       uses l3t:l3-topology-attributes;
     }
     augment "/nd-s:networks/nd-s:network/nd-s:node" {
       when "../nd-s:network-types/l3-unicast-topology" {
         description
           "Augmentation parameters apply only for networks with
           L3 unicast topology";
       }
       description
           "L3 unicast node level attributes ";
       uses l3t:l3-node-attributes;
     }
     augment "/nd-s:networks/nd-s:network/lnk-s:link" {
       when "../nd-s:network-types/l3-unicast-topology" {
         description
           "Augmentation parameters apply only for networks with
           L3 unicast topology";
       }
       description
         "Augment topology link attributes";
       uses l3t:l3-link-attributes;
     }
     augment "/nd-s:networks/nd-s:network/nd-s:node/"
            +"lnk-s:termination-point" {



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       when "../../nd-s:network-types/l3-unicast-topology" {
         description
           "Augmentation parameters apply only for networks with
           L3 unicast topology";
       }
       description "Augment topology termination point configuration";
       uses l3t:l3-termination-point-attributes;
     }
     notification l3-node-event {
       description
         "Notification event for L3 node";
       leaf l3-event-type {
         type l3t:l3-event-type;
         description
           "Event type";
       }
       uses nd-s:node-ref;
       uses l3t:l3-unicast-topology-type;
       uses l3t:l3-node-attributes;
     }
     notification l3-link-event {
       description
         "Notification event for L3 link";
       leaf l3-event-type {
         type l3t:l3-event-type;
         description
           "Event type";
       }
       uses lnk-s:link-ref;
       uses l3t:l3-unicast-topology-type;
       uses l3t:l3-link-attributes;
     }
     notification l3-prefix-event {
       description
         "Notification event for L3 prefix";
       leaf l3-event-type {
         type l3t:l3-event-type;
         description
           "Event type";
       }
       uses nd-s:node-ref;
       uses l3t:l3-unicast-topology-type;
       container prefix {
         description
           "Containing L3 prefix attributes";
         uses l3t:l3-prefix-attributes;
       }
     }



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     notification termination-point-event {
       description
         "Notification event for L3 termination point";
       leaf l3-event-type {
         type l3t:l3-event-type;
         description
           "Event type";
       }
       uses lnk-s:tp-ref;
       uses l3t:l3-unicast-topology-type;
       uses l3t:l3-termination-point-attributes;
     }
   }

   <CODE ENDS>

Appendix B.  Extending the Model

   The model can be extended for specific Layer 3 Unicast types.
   Examples include OSPF and IS-IS topologies.  In the following, one
   additional YANG module is introduced that define simple topology
   model for OSPF.  This module is intended to serve as an example that
   illustrates how the general topology model can be refined across
   multiple levels.  It does not constitute full-fledged OSPF topology
   model which may be more comprehensive and refined than the model that
   is described here.

B.1.  Example OSPF Topology

B.1.1.  Model Overview

   The following model shows how the Layer 3 Unicast topology model can
   be extended to cover OSFP topologies.  For this purpose, a set of
   augmentations are introduced in a separate YANG module, "example-
   ietf-ospf-topology", whose structure is depicted in the following
   diagram.  As before, the notation syntax follows
   [I-D.draft-ietf-netmod-yang-tree-diagrams].














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                        module: example-ietf-ospf-topology
  augment /nd:networks/nd:network/nd:network-types/l3t:l3-unicast-topology:
    +--rw ospf!
  augment /nd:networks/nd:network/l3t:l3-topology-attributes:
    +--rw ospf-topology-attributes
       +--rw area-id?   area-id-type
  augment /nd:networks/nd:network/nd:node/l3t:l3-node-attributes:
    +--rw ospf-node-attributes
       +--rw (router-type)?
       |  +--:(abr)
       |  |  +--rw abr?               empty
       |  +--:(asbr)
       |  |  +--rw asbr?              empty
       |  +--:(internal)
       |  |  +--rw internal?          empty
       |  +--:(pseudonode)
       |     +--rw pseudonode?        empty
       +--rw dr-interface-id?   uint32
  augment /nd:networks/nd:network/lnk:link/l3t:l3-link-attributes:
    +--rw ospf-link-attributes
  augment /l3t:l3-node-event:
    +---- ospf!
    +---- ospf-node-attributes
       +---- (router-type)?
       |  +--:(abr)
       |  |  +---- abr?               empty
       |  +--:(asbr)
       |  |  +---- asbr?              empty
       |  +--:(internal)
       |  |  +---- internal?          empty
       |  +--:(pseudonode)
       |     +---- pseudonode?        empty
       +---- dr-interface-id?   uint32
  augment /l3t:l3-link-event:
    +---- ospf!
    +---- ospf-link-attributes

   The module augments "ietf-l3-unicast-topology" as follows:

   o  A new topology type for an OSPF topology is introduced.

   o  Additional topology attributes are defined in a new grouping which
      augments l3-topology-attributes of the ietf-l3-unicast-topology
      module.  The attributes include an OSPF area-id identifying the
      OSPF area.






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   o  Additional data objects for nodes are introduced by augmenting the
      l3-node-attributes of the l3-unicast-topology module.  New objects
      include router-type and dr-interface-id for pseudonodes.

   o  Links are augmented with ospf link attributes.

   In addition, the module extends notifications for events concerning
   Layer 3 nodes and links with OSPF attributes.

   It should be noted that the model defined here represents topology
   and is intended as an example.  It does not define how to configure
   OSPF routers or interfaces.

B.1.2.  OSPF Topology YANG Module

   The OSPF Topology YANG Module is specified below.  As mentioned, the
   module is intended as an example for how the Layer 3 Unicast topology
   model can be extended to cover OSFP topologies, but it is not
   normative.  Accordingly, the module is not delimited with CODE BEGINS
   and CODE ENDS tags.

                            file "example-ietf-ospf-topology@2017-09-19.yang"
module example-ietf-ospf-topology {
    yang-version 1.1;
    namespace "urn:ietf:params:xml:ns:yang:example-ietf-ospf-topology";
    prefix "ospft";
    import ietf-yang-types {
        prefix "yang";
    }
    import ietf-network {
        prefix "nd";
    }
    import ietf-network-topology {
        prefix "lnk";
    }
    import ietf-l3-unicast-topology {
        prefix "l3t";
    }
    organization
        "IETF I2RS (Interface to the Routing System) Working Group";
    contact
       "WG Web:    <http://tools.ietf.org/wg/i2rs/>
        WG List:   <mailto:i2rs@ietf.org>
        Editor:    Alexander Clemm
                   <mailto:ludwig@clemm.org>
        Editor:    Jan Medved
                   <mailto:jmedved@cisco.com>
        Editor:    Robert Varga



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                   <mailto:robert.varga@pantheon.sk>
        Editor:    Xufeng Liu
                   <mailto:xliu@kuatrotech.com>
        Editor:    Nitin Bahadur
                   <mailto:nitin_bahadur@yahoo.com>
        Editor:    Hariharan Ananthakrishnan
                   <mailto:hari@packetdesign.com>";
    description
       "This module defines a model for OSPF network topologies.
        Copyright (c) 2017 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 Simplified 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
        draft-ietf-i2rs-yang-l3-topology-11;
        see the RFC itself for full legal notices.
        NOTE TO RFC EDITOR: Please replace above reference to
        draft-ietf-i2rs-yang-l3-topology-11 with RFC
        number when published (i.e. RFC xxxx).";
    revision "2017-09-19" {
        description
           "Initial revision.
            NOTE TO RFC EDITOR: Please replace the following reference
            to draft-ietf-i2rs-yang-l3-topology-11 with
            RFC number when published (i.e. RFC xxxx).";
        reference
            "draft-ietf-i2rs-yang-l3-topology-11";
    }
    typedef area-id-type {
        type yang:dotted-quad;
        description
            "Area ID type.";
    }
    grouping ospf-topology-type {
        description
            "Identifies the OSPF topology type.";
        container ospf {
            presence "indiates OSPF Topology";
            description
                "Its presence identifies the OSPF topology type.";
        }
    }
    augment "/nd:networks/nd:network/nd:network-types/"
    + "l3t:l3-unicast-topology" {



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        description
            "Defines the OSPF topology type.";
        uses ospf-topology-type;
    }
    augment "/nd:networks/nd:network/l3t:l3-topology-attributes" {
        when "../nd:network-types/l3t:l3-unicast-topology/ospf" {
            description
                "Augment only for OSPF topology";
            }
        description
            "Augment topology configuration";
        container ospf-topology-attributes {
            description
                "Containing topology attributes";
            leaf area-id {
                type area-id-type;
                description
                    "OSPF area ID";
            }
        }
    }
    augment "/nd:networks/nd:network/nd:node/l3t:l3-node-attributes" {
        when "../../nd:network-types/l3t:l3-unicast-topology/ospf" {
            description
                "Augment only for OSPF topology";
        }
        description
            "Augment node configuration";
        uses ospf-node-attributes;
    }
    augment "/nd:networks/nd:network/lnk:link/l3t:l3-link-attributes" {
        when "../../nd:network-types/l3t:l3-unicast-topology/ospf" {
            description
                "Augment only for OSPF topology";
        }
        description
            "Augment link configuration";
        uses ospf-link-attributes;
    }
    grouping ospf-node-attributes {
        description
            "OSPF node scope attributes";
        container ospf-node-attributes {
            description
                "Containing node attributes";
            choice router-type {
                description
                    "Indicates router type";



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                case abr {
                    leaf abr {
                        type empty;
                        description
                            "The node is ABR";
                    }
                }
                case asbr {
                    leaf asbr {
                        type empty;
                        description
                            "The node is ASBR";
                    }
                }
                case internal {
                    leaf internal {
                        type empty;
                        description
                            "The node is internal";
                    }
                }
                case pseudonode {
                    leaf pseudonode {
                        type empty;
                        description
                            "The node is pseudonode";
                    }
                }
            }
            leaf dr-interface-id {
                when "../pseudonode" {
                    description
                        "Valid only for pseudonode";
                }
                type uint32;
                default "0";
                description
                    "For pseudonodes, DR interface-id";
            }
        }
    }
    grouping ospf-link-attributes {
        description
            "OSPF link scope attributes";
        container ospf-link-attributes {
            description
                "Containing OSPF link attributes";
        }



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    } // ospf-link-attributes
    augment "/l3t:l3-node-event" {
        description
            "OSPF node event";
        uses ospf-topology-type;
        uses ospft:ospf-node-attributes;
    }
    augment "/l3t:l3-link-event" {
        description
            "OSPF link event";
        uses ospf-topology-type;
        uses ospft:ospf-link-attributes;
    }
}



Authors' Addresses

   Alexander Clemm
   Huawei

   EMail: ludwig@clemm.org


   Jan Medved
   Cisco

   EMail: jmedved@cisco.com


   Robert Varga
   Pantheon Technologies SRO

   EMail: robert.varga@pantheon.sk


   Xufeng Liu
   Ericsson

   EMail: xliu@kuatrotech.com


   Hariharan Ananthakrishnan
   Packet Design

   EMail: hari@packetdesign.com




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   Nitin Bahadur
   Bracket Computing

   EMail: nitin_bahadur@yahoo.com















































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