Network Working Group                                           A. Clemm
Internet-Draft                                                    Huawei
Intended status: Standards Track                               J. Medved
Expires: January 3, March 23, 2018                                            Cisco
                                                                R. Varga
                                               Pantheon Technologies SRO
                                                                  X. Liu
                                                                Ericsson
                                                      H. Ananthakrishnan
                                                           Packet Design
                                                              N. Bahadur
                                                       Bracket Computing
                                                            July 2,
                                                      September 19, 2017

                A YANG Data Model for Layer 3 Topologies
                draft-ietf-i2rs-yang-l3-topology-10.txt
                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 http://datatracker.ietf.org/drafts/current/. 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 January 3, 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
   (http://trustee.ietf.org/license-info)
   (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 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.  Definitions and Acronyms  . . . . . . . .  Key Words . . . . . . . . . .   3
   3.  Model Structure . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Layer   3 Unicast Topology Model Overview . . .
   3.  Definitions and Acronyms  . . . . . . . .   5
   5.  Layer 3 Unicast Topology YANG Module . . . . . . . . . .   3
   4.  Model Structure . .   7
   6.  Extending the Model . . . . . . . . . . . . . . . . . . . . .  15
     6.1.  Example 1: OSPF   4
   5.  Layer 3 Unicast Topology Model Overview . . . . . . . . . . .   5
   6.  Layer 3 Unicast Topology YANG Module  . . . . .  15
       6.1.1.  Model Overview . . . . . . .   7
   7.  Interactions with Other YANG Modules  . . . . . . . . . . . .  15
       6.1.2.  OSPF Topology YANG Module . . .
   8.  IANA Considerations . . . . . . . . . . .  17
     6.2.  Example 2: IS-IS Topology . . . . . . . . . .  15
   9.  Security Considerations . . . . . .  22
       6.2.1.  Model Overview . . . . . . . . . . . . .  16
   10. Contributors  . . . . . .  22
       6.2.2.  IS-IS Topology YANG Module . . . . . . . . . . . . .  23
   7.  Interactions with Other YANG Modules . . . . .  17
   11. Acknowledgements  . . . . . . .  28
   8.  IANA Considerations . . . . . . . . . . . . . . .  17
   12. References  . . . . . .  28
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  29
   10. Contributors  17
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     12.2.  Informative References . . . . . .  29
   11. Acknowledgements . . . . . . . . . . .  18
   Appendix A.  Companion YANG model for non-NMDA compliant
                implementations  . . . . . . . . . . .  30
   12. References . . . . . . .  20
   Appendix B.  Extending the Model  . . . . . . . . . . . . . . . .  24
     B.1.  Example OSPF Topology . .  30
     12.1.  Normative References . . . . . . . . . . . . . . . .  24
       B.1.1.  Model Overview  . .  30
     12.2.  Informative References . . . . . . . . . . . . . . . . .  31
   Appendix A.  Companion  24
       B.1.2.  OSPF Topology YANG model for non-NMDA compliant
                implementations  . . . . Module . . . . . . . . . . . . . .  32  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36  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 models are model is introduced that cover IS-IS [RFC1195] and covers OSPF [RFC2328].  Those examples are  This example
   is intended purely for illustrative
   purposes; purpose; we expect that full-blown IS-IS and full-
   blown OSPF models model will be more comprehensive and refined than the examples
   example shown here.

   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 NETCONF [RFC6241].  Some terms, such as datastore and
   data tree, are repeated here for clarity and to put them in context.

   Datastore: A conceptual place to store and access information, such
   as instantiated YANG data.

   Data tree: An instantiated tree of data modeled instantiated management information,
   with YANG, in which individual data items are 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.

   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

3.

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.

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

4.

5.  Layer 3 Unicast Topology Model Overview

   The Layer 3 Unicast topology model is defined by YANG module "ietf-
   l3-unicast-topology" and
   l3-unicast-topology".  Its structure is depicted in the following
   diagram.  Brackets
   enclose list keys, "rw" means configuration, "ro" operational state
   data, "?" designates optional nodes, "*" designates nodes that can
   have multiple instances.  Parantheses enclose choice and case nodes.  The prefix "nd:" refers to the YANG module for networks; the prefix
   "lnk:" refers to the YANG module for network topology.  In the
   interest notation syntax follows
   [I-D.draft-ietf-netmod-yang-tree-diagrams].  For purposes of brevity,
   notifications are not depicted.

   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 metric?   uint32 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)
               +--ro
                +--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.

   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.

5.

6.  Layer 3 Unicast Topology YANG Module

   <CODE BEGINS> file "ietf-l3-unicast-topology@2017-07-02.yang" "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>
        WG Chair:  Susan Hares
                   <mailto:shares@ndzh.com>
        WG Chair:  Russ White
                   <mailto:russ@riw.us>
        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
        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-10;
        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-10
        draft-ietf-i2rs-yang-l3-topology-11 with RFC
        number when published (i.e. RFC xxxx).";
     revision "2017-07-02" "2017-09-19" {
       description
         "Initial revision.
          NOTE TO RFC EDITOR: Please replace the following reference
          to draft-ietf-i2rs-yang-l3-topology-10 draft-ietf-i2rs-yang-l3-topology-11 with
          RFC number when published (i.e. RFC xxxx).";
       reference
         "draft-ietf-i2rs-yang-l3-topology-10";
         "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";
         }
         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
           "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";
         }
         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 metric metric1 {
           type uint32; uint64;
           description
               "Link Metric 1";
         }
         leaf metric2 {
           type uint64;
           description
               "Link Metric"; Metric 2";
         }
       }
     }
     grouping l3-termination-point-attributes {
       description "L3 termination point scope attributes";
       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
         "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;
         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;
     }
   }
   <CODE ENDS>

6.  Extending

7.  Interactions with Other YANG Modules

   As described in section Section 4, the Model

   The model can be extended for specific Layer 3 Unicast types.
   Examples include OSPF builds on top of, and IS-IS topologies.  In
   augments, the following, two
   additional YANG modules are introduced that define simple topology
   models for OSPF and IS-IS, respectively.  These defined in
   [I-D.draft-ietf-i2rs-yang-network-topo].  Specifically, module ietf-
   l3-unicast-topology augments modules intended to
   serve as examples that illustrate how "ietf-network" and "ietf-
   network-topology".  In addition, the general topology model can
   be refined across multiple levels; they do not constitute full-
   fledged OSPF and IS-IS makes use of data types
   that have been defined in [RFC6991].

   The moodel defines a protocol independent YANG data model with layer
   3 topology models which may be more
   comprehensive information.  It is separate from and refined than the not linked with data
   models that are described here.

6.1.  Example 1: OSPF Topology

6.1.1.  Model Overview 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 following model shows how obeys 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 requirements for the following
   diagram.  Like before, brackets enclose list keys, "rw" means
   configuration, "ro" operational ephemeral state data, "?" designates optional
   nodes, "*" designates nodes that can have multiple instances.
   Parantheses enclose choice and case nodes.  A "+" at found in the end of a
   line indicates a line break.

   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
         +--rw multi-topology-id*   uint8
   augment /nd:networks/nd:network/lnk:link/l3t:l3-link-attributes:
      +--rw ospf-link-attributes
         +--rw multi-topology-id?   uint8
   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
         +---- multi-topology-id*   uint8
   augment /l3t:l3-link-event:
      +---- ospf!
      +---- ospf-link-attributes
         +---- multi-topology-id?   uint8

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

   o  A new topology type for an OSPF
   document [I-D.draft-ietf-i2rs-ephemeral-state].  For ephemeral
   topology data that is introduced.

   o  Additional server provided, the process tasked with
   maintaining topology attributes are defined in information will load information from the
   routing process (such as OSPF) into the data model without relying on
   a new grouping which
      augments l3-topology-attributes of configuration datastore.

8.  IANA Considerations

   This document registers the ietf-l3-unicast-topology
      module. following namespace URIs in the "IETF XML
   Registry" [RFC3688]:

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

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

   o  Additional data objects for nodes are introduced by augmenting requested URI is an XML namespace.

   This document registers the
      l3-node-attributes of the l3-unicast-topology module.  New objects
      include router-type, dr-interface-id for pseudonodes, list of
      multi-topology-ids, ospf node capabilities, and traffic
      engineering attributes.

   o  Links are augmented with a multi-topology-id and traffic
      engineering link attributes.

   o  Prefixes are augmented with OSPF specific forwarding address.

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

9.  Security Considerations

   The YANG module extends notifications for events concerning
   Layer 3 nodes, links, termination points, and prefixes with OSPF
   attributes.

   It should be noted that the model defined here represents topology
   and in this document is intended as an example.  It does not define how designed to configure
   OSPF routers be accessed
   via network management protocols such as NETCONF [RFC6241] or interfaces.

6.1.2.  OSPF Topology YANG Module
   RESTCONF [RFC8040].  The OSPF Topology YANG Module lowest NETCONF layer is specified below.  As mentioned, the
   module secure transport
   layer, and the mandatory-to-implement secure transport is intended as an example for how 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
   model can be extended information.  In an NMDA-complient server,
   they are only part of <operational> which provides read-only access
   to cover OSFP topologies, but it is not
   normative.  Accordingly, clients, they are less vulnerable.  That said, the YANG module is not delimited with CODE BEGINS
   and CODE ENDS tags.

   file "example-ietf-ospf-topology@2017-07-02.yang"
   does in principle allow information to be configurable.

   There are a number of data nodes defined in this 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 that are
   writable/creatable/deletable (i.e., config true, which is the Routing System) Working Group";
     contact
       "WG Web:    <http://tools.ietf.org/wg/i2rs/>
        WG List:   <mailto:i2rs@ietf.org>
        WG Chair:  Susan Hares
                   <mailto:shares@ndzh.com>
        WG Chair:  Russ White
                   <mailto:russ@riw.us>
        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
   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 model for OSPF negative
   effect on network topologies.
        Copyright (c) 2017 IETF Trust operations.  These are the subtrees and data nodes
   and their sensitivity/vulnerability in the persons identified as
        authors ietf-network module:

      l3-topology-attributes: A malicious client could attempt to
      sabotage the configuration of any of the code.  All rights reserved.
        Redistribution and use in source and binary forms, with ctonained attributes,
      i.e. the name or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, flag data nodes.

      l3-node-attributes: A malicious client could attempt to sabotage
      the Simplified BSD License
        set forth in Section 4.c configuration of important node attributes, such as the IETF Trust's Legal Provisions
        Relating
      router-id or node prefix.

      l3-link-attributes: A malicious client could attempt to IETF Documents
        (http://trustee.ietf.org/license-info).
        This version sabotage
      the configuration of this YANG module is part important link attributes, such as name,
      flag, and metrics of
        draft-ietf-i2rs-yang-l3-topology-10;
        see the RFC itself for full legal notices.
        NOTE TO RFC EDITOR: Please replace above reference link respectively corresponding data
      nodes.

      l3-termination-point-attributes: A malicious client could attempt
      to
        draft-ietf-i2rs-yang-l3-topology-10 with RFC
        number when published (i.e. RFC xxxx).";
      revision "2017-07-02" {
       description
         "Initial revision.
          NOTE TO RFC EDITOR: Please replace sabotage the following reference
          to draft-ietf-i2rs-yang-l3-topology-10 with
          RFC number when published (i.e. RFC xxxx).";
       reference
         "draft-ietf-i2rs-yang-l3-topology-10";
     }
     typedef area-id-type {
       type yang:dotted-quad;
       description
         "Area ID type.";
     }
     grouping ospf-topology-type {
       description
         "Identifies configuration information of a termination point,
      such as its ip-address and interface name, respectively the OSPF topology type.";
       container ospf {
         presence "indiates OSPF Topology";
         description
           "Its presence identifies
      corresponding data nodes.

10.  Contributors

   The model presented in this document was contributed to by more
   people than can be listed on the OSPF topology type.";
       }
     }
     augment "/nd:networks/nd:network/nd:network-types/"
       + "l3t:l3-unicast-topology" {
       description
         "Defines 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 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 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 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
              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 OSPF topology";
       }
       description
         "Augment link configuration";
       uses ospf-link-attributes;
     }
     grouping ospf-node-attributes {
       description 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.

   [RFC2328]  Moy, J., "OSPF node scope attributes";
       container ospf-node-attributes {
         description
           "Containing node attributes";
         choice router-type {
           description
             "Indicates router type";
           case abr {
             leaf abr {
               type empty;
               description
                 "The node is ABR";
             }
           }
           case asbr {
             leaf asbr {
               type empty;
               description Version 2", RFC 2328, April 1998.

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The node is ASBR";
             }
           }
           case internal {
             leaf internal {
               type empty;
               description Interfaces Group
              MIB", RFC 2863, June 2000.

   [RFC3688]  Mealling, M., "The node is internal";
             }
           }
           case pseudonode {
             leaf pseudonode {
               type empty;
               description IETF XML Registry", RFC 3688, January
              2004.

   [RFC5246]  Dierks, T. and E. Rescorla, "The node is pseudonode";
             }
           }
         }
         leaf dr-interface-id {
           when "../pseudonode" {
             description
               "Valid only Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for pseudonode";

           }
           type uint32;
           default "0";
           description
             "For pseudonodes, DR interface-id";
         }
         leaf-list multi-topology-id {
           type uint8 {
             range "0..127";
           }
           max-elements "128";
           description
             "List of Multi-Topology Identifier up-to 128 (0-127).
              See the
              Network Configuration Protocol (NETCONF)", RFC 4915";
         }
       }
     }
     grouping ospf-link-attributes {
       description
         "OSPF link scope attributes";
       container ospf-link-attributes {
         description
           "Containing OSPF link attributes";
         leaf multi-topology-id {
           type uint8 {
             range "0..127";
           }
           description "Multi topology ID";
         }
       }
     } // 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;
     }
   }

6.2.  Example 2: IS-IS Topology

6.2.1. 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 Overview

   IS-IS topologies are another type 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 Layer 3 Unicast topology.  Like
   in the case I2RS Use Case
              Requirements", I-D draft-ietf-i2rs-usecase-reqs-summary-
              03, November 2016.

   [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 OSPF topology, a Uppercase vs Lowercase in RFC
              2119 Key Words", RFC 8174, May 2017.

Appendix A.  Companion YANG model for IS-IS topology can be non-NMDA compliant implementations

   The YANG module ietf-l3-unicast-topology defined in a separate module which this document
   augments "ietf-l3-unicast-igp-
   topology".  The structure of a corresponding model, "ietf-isis-
   topology", is depicted in the following diagram.  Like before,
   brackets enclose list keys, "rw" means configuration, "ro"
   operational state data, "?" designates optional nodes, "*" designates
   nodes that can have multiple instances.  Parantheses enclose choice two modules, ietf-network and case nodes.  A "+" at the end of a line indicates a line break.

   module: example-ietf-isis-topology
   augment /nd:networks/nd:network/nd:network-types/+
      l3t:l3-unicast-topology:
      +--rw isis!
   augment /nd:networks/nd:network/l3t:l3-topology-attributes:
      +--rw isis-topology-attributes
         +--rw net?   area-address
   augment /nd:networks/nd:network/nd:node/l3t:l3-node-attributes:
      +--rw isis-node-attributes
         +--rw iso
         |  +--rw iso-system-id?       system-id
         |  +--rw iso-pseudonode-id?   iso-pseudonode-id
         +--rw net*                 area-address
         +--rw multi-topology-id*   uint16
         +--rw level?               level
   augment /nd:networks/nd:network/lnk:link/l3t:l3-link-attributes:
      +--rw isis-link-attributes
         +--rw multi-topology-id?   uint16
   augment /l3t:l3-node-event:
      +---- isis!
      +---- isis-node-attributes
         +---- iso
         |  +---- iso-system-id?       system-id
         |  +---- iso-pseudonode-id?   iso-pseudonode-id
         +---- net*                 area-address
         +---- multi-topology-id*   uint16
         +---- level?               level
   augment /l3t:l3-link-event:
      +---- isis!
      +---- isis-link-attributes
         +---- multi-topology-id?   uint16

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

   o  A new topology type is introduced for isis.

   o  Additional topology attributes ietf-network-topology, that
   are introduced designed to be used in a new grouping
      which augments "topology-attributes" of the ietf-l3-unicast-
      topology module.  The attributes include an ISIS NET-id
      identifying the area.

   o  Additional data objects for nodes are introduced by augmenting
      "node-attributes" of conjunction with implementations that
   support the ietf-l3-unicast-topology module.  New
      objects include router-type, iso-system-id Network Management Datastore Architecture (NMDA) defined
   in [I-D.draft-ietf-netmod-revised-datastores].  In order to allow
   implementations to identify use the router, model even in cases when NMDA is not
   supported, a list set of multi-topology-id, companion modules have been defined that
   represent a list state model of NET ids, networks and traffic
      engineering attributes.

   o  Links are augmented with multi-topology-id network topologies, ietf-
   network-state and traffic engineering
      link attributes. ietf-network-topology-state, respectively.

   In addition, the module augments nodes and links with IS-IS
   attributes.

   Again, it should order to be noted that able to use the model for layer 3 topologies defined here represents
   in this in this document in conjunction with non-NMDA compliant
   implementations, a
   topology and is intended as an example.  It does not define how to
   configure IS-IS routers or interfaces.

6.2.2.  IS-IS Topology YANG Module

   The IS-IS Topology YANG Module is specified as follows.  As
   mentioned, the corresponding companion module is intended needs to be
   introduced as an example 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 how any modules that augment ietf-l3-
   unicast-topology, such as the Layer 3
   Unicast topology model can be extended example modules defined in see
   Appendix B, example-ietf-ospf-topology.  For non-NMDA compliant
   implementations, companion modules will need to cover IS-IS topologies, but
   it is 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 normative.  Accordingly, 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 delimited with
   CODE BEGINS and CODE ENDS tags.
   depicted separately.

   <CODE BEGINS> file "example-ietf-isis-topology@2017-07-02.yang" "ietf-l3-unicast-topology-state@2017-09-19.yang"
   module example-ietf-isis-topology ietf-l3-unicast-topology-state {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:example-ietf-isis-topology";
       "urn:ietf:params:xml:ns:yang:ietf-l3-unicast-topology-state";
     prefix "isist"; "l3t-s";
     import ietf-network ietf-network-state {
       prefix "nd"; "nd-s";
     }
     import ietf-network-topology ietf-network-topology-state {
       prefix "lnk"; "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>
        WG Chair:  Susan Hares
                   <mailto:shares@ndzh.com>
        WG Chair:  Russ White
                   <mailto:russ@riw.us>
        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 IS-IS network topologies. 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-10;
        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-10
        draft-ietf-i2rs-yang-l3-topology-11 with RFC
        number when published (i.e. RFC xxxx).";
     revision "2017-07-02" "2017-09-19" {
       description
         "Initial revision.
          NOTE TO RFC EDITOR: Please replace the following reference
          to draft-ietf-i2rs-yang-l3-topology-10 draft-ietf-i2rs-yang-l3-topology-11 with
          RFC number when published (i.e. RFC xxxx).";
       reference
         draft-ietf-i2rs-yang-l3-topology-10;
         "draft-ietf-i2rs-yang-l3-topology-11";
     }
     typedef iso-pseudonode-id {
       type string

     augment "/nd-s:networks/nd-s:network/nd-s:network-types" {
         pattern '[0-9a-fA-F]{2}';

       }
       description
            "ISO pseudonode id
         "Introduce new network type for broadcast network."; L3 unicast topology";
       uses l3t:l3-unicast-topology-type;
     }
     typedef area-address{
       type string {
         pattern '[0-9A-Fa-f]{2}\.([0-9A-Fa-f]{4}\.){0,3}';
       }
       description
         "This type defines the area address.";
     }
     typedef system-id {
       type string {
         pattern
          '[0-9A-Fa-f]{4}\.[0-9A-Fa-f]{4}\.[0-9A-Fa-f]{4}';
       }
       description
        "This type defines ISIS system id using a pattern;
         an example of a system id looks like: 0143.0438.AeF0.";
     }
     typedef level {
       type enumeration {
         enum "level-1"
     augment "/nd-s:networks/nd-s:network" {
           description
            "This enum describes L1 only capability.";
         }
         enum "level-2"
       when "nd-s:network-types/l3-unicast-topology" {
         description
            "This enum describes L2
           "Augmentation parameters apply only capability.";
         }
         enum "level-all" {
           description
            "This enum describes both levels (L1 and L2) capability.";
         }
       }
       default "level-all";
       description
        "This type defines the ISIS level of an object.";
     }
     grouping isis-topology-type {
       description
         "Identifies the ISIS topology type.";
       container isis {
         presence "Indicates ISIS Topology";
         description
           "Its presence identifies the ISIS topology type.";
       } for networks with
           L3 unicast topology";
       }
     augment "/nd:networks/nd:network/nd:network-types/"
       +"l3t:l3-unicast-topology" {
       description
         "Defines
           "L3 unicast for the ISIS topology type."; network as a whole";
       uses isis-topology-type; l3t:l3-topology-attributes;
     }
     augment "/nd:networks/nd:network/l3t:l3-topology-attributes" "/nd-s:networks/nd-s:network/nd-s:node" {
       when "../nd:network-types/l3t:l3-unicast-topology/isis" "../nd-s:network-types/l3-unicast-topology" {
         description
           "Augment
           "Augmentation parameters apply only for ISIS networks with
           L3 unicast topology";
       }
       description
         "Augment topology configuration";
       container isis-topology-attributes {
         description
           "Containing topology attributes";
         leaf net {
           type area-address;
           description
             "ISO NET ID value";
         }
       }
           "L3 unicast node level attributes ";
       uses l3t:l3-node-attributes;
     }
     augment "/nd:networks/nd:network/nd:node/"+
       "l3t:l3-node-attributes" "/nd-s:networks/nd-s:network/lnk-s:link" {
       when "../../nd:network-types/l3t:l3-unicast-topology/isis" "../nd-s:network-types/l3-unicast-topology" {
         description
           "Augment
           "Augmentation parameters apply only for ISIS networks with
           L3 unicast topology";
       }
       description
         "Augment node configuration"; topology link attributes";
       uses isis-node-attributes; l3t:l3-link-attributes;
     }
     augment "/nd:networks/nd:network/lnk:link/l3t:l3-link-attributes" "/nd-s:networks/nd-s:network/nd-s:node/"
            +"lnk-s:termination-point" {

       when "../../nd:network-types/l3t:l3-unicast-topology/isis" "../../nd-s:network-types/l3-unicast-topology" {
         description
           "Augment
           "Augmentation parameters apply only for ISIS networks with
           L3 unicast topology";
       }
       description "Augment link topology termination point configuration";
       uses isis-link-attributes; l3t:l3-termination-point-attributes;
     }
     grouping isis-node-attributes {
       description
         "ISIS node scope attributes";
       container isis-node-attributes {
         description
           "Containing node attributes";

         container iso
     notification l3-node-event {
       description
             "Containing ISO atrributes";
         "Notification event for L3 node";
       leaf iso-system-id l3-event-type {
         type system-id; l3t:l3-event-type;
         description
               "ISO system ID";
           "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 iso-pseudonode-id l3-event-type {
         type iso-pseudonode-id;
             default "00"; l3t:l3-event-type;
         description
               "Pseudonode ID";
           "Event type";
       }
       uses lnk-s:link-ref;
       uses l3t:l3-unicast-topology-type;
       uses l3t:l3-link-attributes;
     }
         leaf-list net
     notification l3-prefix-event {
           type area-address;
           max-elements 3;
       description
             "List of ISO NET IDs";
         }
         leaf-list multi-topology-id
         "Notification event for L3 prefix";
       leaf l3-event-type {
         type uint16 {
             range "0..4095";
           }
           max-elements "128"; l3t:l3-event-type;
         description
             "List of Multi Topology Identifier up to 128 (0-127).
             RFC 4915";
           "Event type";
       }
         leaf level
       uses nd-s:node-ref;
       uses l3t:l3-unicast-topology-type;
       container prefix {
           type level;
         description "Level 1, Level 2 or Level 1 and 2";
         }
           "Containing L3 prefix attributes";
         uses l3t:l3-prefix-attributes;
       }
     }
     grouping isis-link-attributes {
       description
         "ISIS link scope attributes";
       container isis-link-attributes
     notification termination-point-event {
       description
           "Containing link attributes";
         "Notification event for L3 termination point";
       leaf multi-topology-id l3-event-type {
         type uint16 {
             range "0..4095";
           } l3t:l3-event-type;
         description
             "Multi topology ID";

         }
       }
           "Event type";
       }
     augment "/l3t:l3-node-event" {
       description
         "ISIS node event";
       uses isis-topology-type;
       uses isis-node-attributes;
     }
     augment "/l3t:l3-link-event" {
       description
         "ISIS link event"; lnk-s:tp-ref;
       uses isis-topology-type; l3t:l3-unicast-topology-type;
       uses isis-link-attributes; l3t:l3-termination-point-attributes;
     }
   }

7.  Interactions with Other YANG Modules

   As described in section Section 3, 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-10.txt (RFC form)

   Name: ietf-l3-unicast-topology-state
   Namespace: urn:ietf:params:xml:ns:yang:ietf-l3-unicast-topology-state
   Prefix: l3t-s
   Reference: draft-ietf-i2rs-yang-l3-topology-10.txt (RFC form)

9.  Security Considerations

   The YANG module defined in this memo is designed to be accessed via
   the NETCONF protocol [RFC6241].  The lowest NETCONF layer is the
   secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The NETCONF access
   control model [RFC6536] provides the means to restrict access for
   particular NETCONF users to a pre-configured subset of all available
   NETCONF protocol operations and content.

   In general, Layer 3 Unicast topologies are server-provided and
   provide ephemeral topology information.  As they provide read-only
   access to clients, they are less vulnerable.  That said, the YANG
   module does in principle allow information to be configurable in
   certain instances (when the server-provided flag for the topology is
   set to false).  In such cases, a malicious client could introduce
   topologies that are undesired.  For example, a client could remove or
   add topological links between nodes, which could lead to an undesired
   and suboptimal topology, which might impact service levels and
   network utilization.  It is therefore important that the NETCONF
   access control model is vigorously applied to prevent topology
   configuration by unauthorized clients.

10.  Contributors

   The model presented in this paper 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 Ladislav Lhotka, Andy Bierman,
   Carlos Pignataro, Joel Halpern, Juergen Schoenwaelder, Alia Atlas,
   Susan Hares, Benoit Claise, and Carl Moberg.

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-14, June 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.

   [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.

   [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.

   [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

   <CODE ENDS>

Appendix B.  Extending the Model

   The model can be extended for Routing
              Management", RFC 8022, November 2016.

Appendix A.  Companion 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 non-NMDA compliant implementations 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 ietf-l3-unicast-topology defined module, "example-
   ietf-ospf-topology", whose structure is depicted in this document the following
   diagram.  As before, the notation syntax follows
   [I-D.draft-ietf-netmod-yang-tree-diagrams].

                        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 two modules, ietf-network and ietf-network-topology, that "ietf-l3-unicast-topology" as follows:

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

   o  Additional topology attributes 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 new grouping which
      augments l3-topology-attributes 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, ietf-l3-unicast-topology
      module.  The attributes include an OSPF area-id identifying the module
   augments ietf-network-state and ietf-network-topology-state (instead
   of ietf-network and ietf-network-state) and all of its
      OSPF area.

   o  Additional data objects for nodes are
   non-configurable.

   Similar considerations apply for any modules that augment ietf-l3-
   unicast-topology, such as the example modules defined earlier,
   example-ietf-ospf-topology and example-ietf-isis-topology.  For non-
   NMDA compliant implementations, companion modules will need to be introduced that represent state information and are non-configurable, by augmenting ietf-l3-unicast-topology-state instead the
      l3-node-attributes of ietf-l3-unicast-
   topology.  Because they served as examples only, companion modules the l3-unicast-topology module.  New objects
      include router-type and dr-interface-id for those examples pseudonodes.

   o  Links are not given.

   Like ietf-network-state augmented with ospf link attributes.

   In addition, the module extends notifications for events concerning
   Layer 3 nodes and ietf-network-topology-state, ietf-l3-
   unicast-topology SHOULD NOT links with OSPF attributes.

   It should be supported by implementations noted that
   support NMDA. 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 for this reason that specified below.  As mentioned, the
   module is defined in
   the Appendix.

   The definition of the module follows below.  As intended as an example for how the structure of Layer 3 Unicast topology
   model can be extended to cover OSFP topologies, but it is not
   normative.  Accordingly, the module mirrors that of its underlying module, the YANG tree is not
   depicted separately.

   <CODE BEGINS> delimited with CODE BEGINS
   and CODE ENDS tags.

                            file "ietf-l3-unicast-topology-state@2017-07-02.yang" "example-ietf-ospf-topology@2017-09-19.yang"
module ietf-l3-unicast-topology-state example-ietf-ospf-topology {
    yang-version 1.1;
    namespace
       "urn:ietf:params:xml:ns:yang:ietf-l3-unicast-topology-state"; "urn:ietf:params:xml:ns:yang:example-ietf-ospf-topology";
    prefix "l3t-s"; "ospft";
    import ietf-network-state ietf-yang-types {
        prefix "nd-s"; "yang";
    }
    import ietf-network-topology-state ietf-network {
        prefix "lnk-s"; "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>
        WG Chair:  Susan Hares
                   <mailto:shares@ndzh.com>
        WG Chair:  Russ White
                   <mailto:russ@riw.us>
        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). 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-10;
        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-10
        draft-ietf-i2rs-yang-l3-topology-11 with RFC
        number when published (i.e. RFC xxxx).";
    revision "2017-07-02" "2017-09-19" {
        description
           "Initial revision.
            NOTE TO RFC EDITOR: Please replace the following reference
            to draft-ietf-i2rs-yang-l3-topology-10 draft-ietf-i2rs-yang-l3-topology-11 with
            RFC number when published (i.e. RFC xxxx).";
        reference
         "draft-ietf-i2rs-yang-l3-topology-10";
            "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-s:networks/nd-s:network/nd-s:network-types" "/nd:networks/nd:network/nd:network-types/"
    + "l3t:l3-unicast-topology" {
        description
         "Introduce new network type for L3 unicast topology";
            "Defines the OSPF topology type.";
        uses l3t:l3-unicast-topology-type; ospf-topology-type;
    }
    augment "/nd-s:networks/nd-s:network" "/nd:networks/nd:network/l3t:l3-topology-attributes" {
        when "nd-s:network-types/l3-unicast-topology" "../nd:network-types/l3t:l3-unicast-topology/ospf" {
            description
           "Augmentation parameters apply
                "Augment only for networks with
           L3 unicast OSPF 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"
            "Augment topology configuration";
        container ospf-topology-attributes {
       when "../nd-s:network-types/l3-unicast-topology"
            description
                "Containing topology attributes";
            leaf area-id {
                type area-id-type;
                description
           "Augmentation parameters apply only for networks with
           L3 unicast topology";
                    "OSPF area ID";
            }
        }
       description
           "L3 unicast node level attributes ";
       uses l3t:l3-node-attributes;
    }
    augment "/nd-s:networks/nd-s:network/lnk-s:link" "/nd:networks/nd:network/nd:node/l3t:l3-node-attributes" {
        when "../nd-s:network-types/l3-unicast-topology" "../../nd:network-types/l3t:l3-unicast-topology/ospf" {
            description
           "Augmentation parameters apply
                "Augment only for networks with
           L3 unicast OSPF topology";
        }
        description
            "Augment topology link attributes"; node configuration";
        uses l3t:l3-link-attributes; ospf-node-attributes;
    }
    augment "/nd-s:networks/nd-s:network/nd-s:node/"
            +"lnk-s:termination-point" "/nd:networks/nd:network/lnk:link/l3t:l3-link-attributes" {
        when "../../nd-s:network-types/l3-unicast-topology" "../../nd:network-types/l3t:l3-unicast-topology/ospf" {
            description
           "Augmentation parameters apply
                "Augment only for networks with
           L3 unicast OSPF topology";
        }
        description
            "Augment topology termination point link configuration";
        uses l3t:l3-termination-point-attributes; ospf-link-attributes;
    }
     notification l3-node-event
    grouping ospf-node-attributes {
        description
         "Notification event for L3 node";
            "OSPF node scope attributes";
        container ospf-node-attributes {
            description
                "Containing node attributes";
            choice router-type {
                description
                    "Indicates router type";

                case abr {
                    leaf l3-event-type abr {
                        type l3t:l3-event-type; empty;
                        description
           "Event type";
                            "The node is ABR";
                    }
       uses nd-s:node-ref;
       uses l3t:l3-unicast-topology-type;
       uses l3t:l3-node-attributes;
                }
     notification l3-link-event
                case asbr {
                    leaf asbr {
                        type empty;
                        description
         "Notification event for L3 link";
                            "The node is ASBR";
                    }
                }
                case internal {
                    leaf l3-event-type internal {
                        type l3t:l3-event-type; empty;
                        description
           "Event type";
                            "The node is internal";
                    }
       uses lnk-s:link-ref;
       uses l3t:l3-unicast-topology-type;
       uses l3t:l3-link-attributes;
                }
     notification l3-prefix-event
                case pseudonode {
                    leaf pseudonode {
                        type empty;
                        description
         "Notification event for L3 prefix";
                            "The node is pseudonode";
                    }
                }
            }
            leaf l3-event-type dr-interface-id {
                when "../pseudonode" {
                    description
                        "Valid only for pseudonode";
                }
                type l3t:l3-event-type; uint32;
                default "0";
                description
           "Event type";
                    "For pseudonodes, DR interface-id";
            }
       uses nd-s:node-ref;
       uses l3t:l3-unicast-topology-type;
        }
    }
    grouping ospf-link-attributes {
        description
            "OSPF link scope attributes";
        container prefix ospf-link-attributes {
            description
                "Containing L3 prefix OSPF link attributes";
         uses l3t:l3-prefix-attributes;
        }

    }
     notification termination-point-event // ospf-link-attributes
    augment "/l3t:l3-node-event" {
        description
         "Notification event for L3 termination point";
       leaf l3-event-type
            "OSPF node event";
        uses ospf-topology-type;
        uses ospft:ospf-node-attributes;
    }
    augment "/l3t:l3-link-event" {
         type l3t:l3-event-type;
        description
           "Event type";
       }
       uses lnk-s:tp-ref;
            "OSPF link event";
        uses l3t:l3-unicast-topology-type; ospf-topology-type;
        uses l3t:l3-termination-point-attributes; ospft:ospf-link-attributes;
    }
}

   <CODE ENDS>

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
   Nitin Bahadur
   Bracket Computing

   EMail: nitin_bahadur@yahoo.com