Internet Engineering Task Force (IETF) A. Clemm

Internet Engineering Task Force (IETF) A. Clemm
Request for Comments: 8346 Huawei
Category: Standards Track J. Medved
ISSN: 2070-1721 Cisco
R. Varga
Pantheon Technologies SRO
X. Liu
Jabil
H. Ananthakrishnan
Packet Design
N. Bahadur
Bracket Computing
March 2018

A YANG Data Model for Layer 3 Topologies

Abstract

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

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8346.

Clemm, et al. Standards Track [Page 1]

RFC 8346 YANG Data Model for L3 Topologies March 2018

Copyright Notice

Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include 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 ....................................................3
2. Key Words .......................................................3
3. Definitions and Acronyms ........................................4
4. Model Structure .................................................5
5. Layer 3 Unicast Topology Model Overview .........................6
6. Layer 3 Unicast Topology YANG Module ............................7
7. Interactions with Other YANG Modules ...........................15
8. IANA Considerations ............................................15
9. Security Considerations ........................................16
10. References ....................................................17
10.1. Normative References .....................................17
10.2. Informative References ...................................19
Appendix A. Companion YANG Data Model for Implementations Not
Compliant with NMDA ..................................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
Appendix C. An Example ...........................................29
Acknowledgments ...................................................34
Contributors ......................................................34
Authors' Addresses ................................................35

Clemm, et al. Standards Track [Page 2]

RFC 8346 YANG Data Model for L3 Topologies March 2018

1. Introduction

This document introduces a YANG [RFC7950] [RFC6991] data model for
Layer 3 (L3) 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 [RFC8345].

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

There are multiple applications for a topology data model. A number
of use cases have been defined in Section 6 of [USECASE-REQS]. 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 the YANG module "ietf-l3-unicast-topology".
This YANG module augments the general network topology model defined
in [RFC8345] with information specific to Layer 3 Unicast. In 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 [YANG-TE] and is 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.

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3. Definitions and Acronyms

This document defines a YANG data model and thus uses many terms
defined in YANG [RFC7950] and NETCONF [RFC6241]. Some terms, such as
"datastore" and "data tree", are repeated here for clarity and
context.

Datastore: A conceptual place to store and access information. A
datastore might be implemented, for example, using files, a
database, flash memory locations, or combinations thereof. A
datastore maps to an instantiated YANG data tree (definition
adopted from [RFC8342]).

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

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

TED: Traffic Engineering Database

YANG: YANG is a data modeling language used to model configuration
data, state data, Remote Procedure Calls, and notifications for
network management protocols [RFC7950].

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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 | |
| +----------+------------+ |
+-------------^---------------+
|
|
+------------^-------------+
| ietf-l3-unicast-topology |
+------------^-------------+
|
|
+-----------^-----------+
| example-ospf-topology |
+-----------------------+

Figure 1: Overall Model Structure

YANG modules "ietf-network" and "ietf-network-topology" collectively
define the basic network topology model [RFC8345]. 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 IS-IS topologies.

The YANG modules "ietf-network" and "ietf-network-topology" are
designed to be used in conjunction with implementations that support
the Network Management Datastore Architecture (NMDA) defined in
[RFC8342]. 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 Appendix A.

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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 [RFC8340]. For
purposes of brevity, notifications are not depicted.

module: ietf-l3-unicast-topology
augment /nw:networks/nw:network/nw:network-types:
+--rw l3-unicast-topology!
augment /nw:networks/nw:network:
+--rw l3-topology-attributes
+--rw name? string
+--rw flag* l3-flag-type
augment /nw:networks/nw:network/nw:node:
+--rw l3-node-attributes
+--rw name? inet:domain-name
+--rw flag* node-flag-type
+--rw router-id* rt-types:router-id
+--rw prefix* [prefix]
+--rw prefix inet:ip-prefix
+--rw metric? uint32
+--rw flag* prefix-flag-type
augment /nw:networks/nw:network/nt:link:
+--rw l3-link-attributes
+--rw name? string
+--rw flag* link-flag-type
+--rw metric1? uint64
+--rw metric2? uint64
augment /nw:networks/nw:network/nw:node/nt: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.

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o Additional topology attributes are introduced, defined in a
grouping that augments the "network" list of the network module.
The attributes include a name for the topology and a set of flags
(represented by a leaf-list). Each type of flag is represented by
a separate identity. This allows additional flags to be
introduced 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 a set of
flags and a list of prefixes. Each prefix 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 that allow a link to be associated with a link
name, another set of flags, and a link metric.

o Termination points (in the "ietf-network-topology" module) 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, link, prefix, or termination point. Also, as a
convenience to applications, additional data of the affected node,
link, prefix, or termination point is included. While this makes
notifications larger in volume than they need to be, it avoids the
need for subsequent retrieval of context information that might have
changed in the meantime.

6. Layer 3 Unicast Topology YANG Module

This YANG module makes reference to the following documents:
[RFC2863] and [RFC8343].

<CODE BEGINS> file "[email protected]"
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 "nw";
}
import ietf-network-topology {
prefix "nt";
}

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import ietf-inet-types {
prefix "inet";
}
import ietf-routing-types {
prefix "rt-types";
}
organization
"IETF I2RS (Interface to the Routing System) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/i2rs/>
WG List: <mailto:[email protected]>
Editor: Alexander Clemm
<mailto:[email protected]>
Editor: Jan Medved
<mailto:[email protected]>
Editor: Robert Varga
<mailto:[email protected]>
Editor: Xufeng Liu
<mailto:[email protected]>
Editor: Nitin Bahadur
<mailto:[email protected]>
Editor: Hariharan Ananthakrishnan
<mailto:[email protected]>";
description
"This module defines a model for Layer 3 Unicast
topologies.

Copyright (c) 2018 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
(https://trustee.ietf.org/license-info).

This version of this YANG module is part of
RFC 8346; see the RFC itself for full legal notices.";
revision "2018-02-26" {
description
"Initial revision.";
reference
"RFC 8346: A YANG Data Model for Layer 3 Topologies";
}

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

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}

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

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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 "Identifies 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 "Contains 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 {

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description "L3 node scope attributes";
container l3-node-attributes {
description
"Contains 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 rt-types:router-id;
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
"Contains 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";
}

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RFC 8346 YANG Data Model for L3 Topologies March 2018

leaf metric2 {
type uint64;
description
"Link Metric 2";
}
}
}
grouping l3-termination-point-attributes {
description "L3 termination point scope attributes";
container l3-termination-point-attributes {
description
"Contains 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
"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 interface-ref defined
in RFC 8343. It should be noted that data type
interface-ref of RFC 8343 cannot be used directly,

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RFC 8346 YANG Data Model for L3 Topologies March 2018

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.";
reference
"RFC 8343: A YANG Data Model for Interface Management";
}
}
}
}
}
augment "/nw:networks/nw:network/nw:network-types" {
description
"Introduces new network type for L3 Unicast topology";
uses l3-unicast-topology-type;
}
augment "/nw:networks/nw:network" {
when "nw:network-types/l3t: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 "/nw:networks/nw:network/nw:node" {
when "../nw:network-types/l3t: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 "/nw:networks/nw:network/nt:link" {
when "../nw:network-types/l3t:l3-unicast-topology" {
description
"Augmentation parameters apply only for networks with
L3 Unicast topology";
}
description
"Augments topology link attributes";
uses l3-link-attributes;
}
augment "/nw:networks/nw:network/nw:node/"
+"nt:termination-point" {
when "../../nw:network-types/l3t:l3-unicast-topology" {

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description
"Augmentation parameters apply only for networks with
L3 Unicast topology";
}
description "Augments 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 nw: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 nt: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 nw:node-ref;
uses l3-unicast-topology-type;
container prefix {
description
"Contains L3 prefix attributes";
uses l3-prefix-attributes;
}
}
notification termination-point-event {

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

<CODE ENDS>

7. Interactions with Other YANG Modules

As described in Section 4, the model defined in this document builds
on top of, and augments, the YANG modules defined in [RFC8345].
Specifically, the "ietf-l3-unicast-topology" module augments the
"ietf-network" and "ietf-network-topology" modules. In addition, the
model makes use of data types defined in [RFC6991].

The model defined in this document is 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, e.g., "ietf-routing" [RFC8022] and
"ietf-rib-extension" [YANG-RIB]. That said, the model does import a
type definition from model "ietf-routing-types" [RFC8294].

The model complies with the requirements for the ephemeral state
found in [RFC8242]. 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.

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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: RFC 8346

Name: ietf-l3-unicast-topology-state
Namespace: urn:ietf:params:xml:ns:yang:ietf-l3-unicast-topology-state
Prefix: l3t-s
Reference: RFC 8346

9. Security Considerations

The YANG modules specified in this document define a schema for data
that 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 [RFC8341] provides the means to
restrict access for particular NETCONF or RESTCONF users to a
preconfigured subset of all available NETCONF or RESTCONF protocol
operations and content.

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

There are a number of data nodes defined in these YANG modules 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-l3-unicast-topology"
module:

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

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

o 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.

o l3-termination-point-attributes: A malicious client could attempt
to sabotage the configuration information of a termination point,
such as the termination point's IP address and interface name.

10. References

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.

[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
<https://www.rfc-editor.org/info/rfc2863>.

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

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.

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

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

Clemm, et al. Standards Track [Page 17]

RFC 8346 YANG Data Model for L3 Topologies March 2018

[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.

[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.

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

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

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

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8294] Liu, X., Qu, Y., Lindem, A., Hopps, C., and L. Berger,
"Common YANG Data Types for the Routing Area", RFC 8294,
DOI 10.17487/RFC8294, December 2017,
<https://www.rfc-editor.org/info/rfc8294>.

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

[RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore Architecture
(NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
<https://www.rfc-editor.org/info/rfc8342>.

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

Clemm, et al. Standards Track [Page 18]

RFC 8346 YANG Data Model for L3 Topologies March 2018

10.2. Informative References

[RFC8022] Lhotka, L. and A. Lindem, "A YANG Data Model for Routing
Management", RFC 8022, DOI 10.17487/RFC8022, November
2016, <https://www.rfc-editor.org/info/rfc8022>.

[RFC8242] Haas, J. and S. Hares, "Interface to the Routing System
(I2RS) Ephemeral State Requirements", RFC 8242,
DOI 10.17487/RFC8242, September 2017,
<https://www.rfc-editor.org/info/rfc8242>.

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

[RFC8343] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
<https://www.rfc-editor.org/info/rfc8343>.

[USECASE-REQS]
Hares, S. and M. Chen, "Summary of I2RS Use Case
Requirements", Work in Progress, draft-ietf-i2rs-usecase-
reqs-summary-03, November 2016.

[YANG-RIB] Lindem, A. and Y. Qu, "RIB YANG Data Model", Work in
Progress, draft-acee-rtgwg-yang-rib-extend-06, January
2018.

[YANG-TE] Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
O. Gonzalez de Dios, "YANG Data Model for Traffic
Engineering (TE) Topologies", Work in Progress,
draft-ietf-teas-yang-te-topo-15, February 2018.

Clemm, et al. Standards Track [Page 19]

RFC 8346 YANG Data Model for L3 Topologies March 2018

Appendix A. Companion YANG Data Model for Implementations Not Compliant
with NMDA

The YANG module "ietf-l3-unicast-topology" defined in this document
augments two modules defined in [RFC8345]: "ietf-network" and
"ietf-network-topology". These two modules were designed to be used
in conjunction with implementations that support the Network
Management Datastore Architecture (NMDA) defined in [RFC8342]. In
order to allow implementations to use the model in cases when NMDA is
not supported, [RFC8345] defines two companion modules,
"ietf-network- state" and "ietf-network-topology-state", that
represent state models of networks and network topologies,
respectively.

In order to be able to use the model for Layer 3 topologies defined
in this document in conjunction with implementations not compliant
with NMDA, 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-topology"), and all of its data
nodes are non-configurable.

Similar considerations apply to any module that augments "ietf-l3-
unicast-topology", such as the example module defined in Appendix B
(i.e., example-ospf-topology). For implementations that are not
compliant with NMDA, companion modules that represent state
information and that are non-configurable will need to be introduced.
These modules augment "ietf-l3-unicast-topology-state" instead of
"ietf-l3-unicast-topology". Companion modules for the example module
defined in Appendix B are not provided (since it is just an example).

Like "ietf-network-state" and "ietf-network-topology-state",
"ietf-l3-unicast-topology" SHOULD NOT be supported by implementations
that support NMDA. The module is therefore defined in an 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 "[email protected]"
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 "nw-s";

Clemm, et al. Standards Track [Page 20]

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}
import ietf-network-topology-state {
prefix "nt-s";
}
import ietf-l3-unicast-topology {
prefix "l3t";
}
organization
"IETF I2RS (Interface to the Routing System) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/i2rs/>
WG List: <mailto:[email protected]>
Editor: Alexander Clemm
<mailto:[email protected]>
Editor: Jan Medved
<mailto:[email protected]>
Editor: Robert Varga
<mailto:[email protected]>
Editor: Xufeng Liu
<mailto:[email protected]>
Editor: Nitin Bahadur
<mailto:[email protected]>
Editor: Hariharan Ananthakrishnan
<mailto:[email protected]>";
description
"This module defines a model for Layer 3 Unicast topology
state, representing topology that either is learned or
results from applying topology that has been configured per
the 'ietf-l3-unicast-topology' model, mirroring the
corresponding data nodes in this model.

This 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) 2018 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
(https://trustee.ietf.org/license-info).

This version of this YANG module is part of RFC 8346;
see the RFC itself for full legal notices.";

Clemm, et al. Standards Track [Page 21]

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revision "2018-02-26" {
description
"Initial revision.";
reference
"RFC 8346: A YANG Data Model for Layer 3 Topologies";
}
augment "/nw-s:networks/nw-s:network/nw-s:network-types" {
description
"Introduce new network type for L3 Unicast topology";
uses l3t:l3-unicast-topology-type;
}
augment "/nw-s:networks/nw-s:network" {
when "nw-s:network-types/l3t-s: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 "/nw-s:networks/nw-s:network/nw-s:node" {
when "../nw-s:network-types/l3t-s: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 "/nw-s:networks/nw-s:network/nt-s:link" {
when "../nw-s:network-types/l3t-s:l3-unicast-topology" {
description
"Augmentation parameters apply only for networks with
L3 Unicast topology";
}
description
"Augments topology link attributes";
uses l3t:l3-link-attributes;
}
augment "/nw-s:networks/nw-s:network/nw-s:node/"
+"nt-s:termination-point" {
when "../../nw-s:network-types/l3t-s:l3-unicast-topology" {
description
"Augmentation parameters apply only for networks with
L3 Unicast topology";
}

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description "Augments 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 nw-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 nt-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 nw-s:node-ref;
uses l3t:l3-unicast-topology-type;
container prefix {
description
"Contains L3 prefix attributes";
uses l3t:l3-prefix-attributes;
}
}
notification termination-point-event {
description
"Notification event for L3 termination point";
leaf l3-event-type {
type l3t:l3-event-type;

Clemm, et al. Standards Track [Page 23]

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description
"Event type";
}
uses nt-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. This appendix introduces
a YANG module that defines a 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 a 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, in this case, to cover OSPF topologies. For this
purpose, a set of augmentations are introduced in a separate YANG
module, "example-ospf-topology", whose structure is depicted in the
following diagram. As before, the notation syntax follows [RFC8340].
Note that one of the lines has been wrapped to adhere to the
72-character line limitation of RFCs.

Clemm, et al. Standards Track [Page 24]

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module: example-ospf-topology
augment /nw:networks/nw:network/nw:network-types/
l3t:l3-unicast-topology:
+--rw ospf!
augment /nw:networks/nw:network/l3t:l3-topology-attributes:
+--rw ospf-topology-attributes
+--rw area-id? area-id-type
augment /nw:networks/nw:network/nw: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 /nw:networks/nw:network/nt: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 that
augments l3-topology-attributes of the "ietf-l3-unicast-topology"
module. The attributes include an OSPF area-id identifying the
OSPF area.

Clemm, et al. Standards Track [Page 25]

RFC 8346 YANG Data Model for L3 Topologies March 2018

o Additional data objects for nodes are introduced by augmenting the
l3-node-attributes of the "ietf-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 OSPF topologies, but it is not
normative. Accordingly, the module is not delimited with
<CODE BEGINS> and <CODE ENDS> tags.

file "[email protected]"
module example-ospf-topology {
yang-version 1.1;
namespace "urn:example:example-ospf-topology";
prefix "ex-ospft";
import ietf-yang-types {
prefix "yang";
}
import ietf-network {
prefix "nw";
}
import ietf-network-topology {
prefix "nt";
}
import ietf-l3-unicast-topology {
prefix "l3t";
}
description
"This module is intended as an example for how the
Layer 3 Unicast topology model can be extended to cover
OSPF topologies.";
typedef area-id-type {
type yang:dotted-quad;
description
"Area ID type.";
}
grouping ospf-topology-type {

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RFC 8346 YANG Data Model for L3 Topologies March 2018

description
"Identifies the OSPF topology type.";
container ospf {
presence "indicates OSPF Topology";
description
"Its presence identifies the OSPF topology type.";
}
}
augment "/nw:networks/nw:network/nw:network-types/"
+ "l3t:l3-unicast-topology" {
description
"Defines the OSPF topology type.";
uses ospf-topology-type;
}
augment "/nw:networks/nw:network/l3t:l3-topology-attributes" {
when "../nw:network-types/l3t:l3-unicast-topology/" +
"ex-ospft:ospf" {
description
"Augments only for OSPF topology";
}
description
"Augments topology configuration";
container ospf-topology-attributes {
description
"Contains topology attributes";
leaf area-id {
type area-id-type;
description
"OSPF area ID";
}
}
}
augment "/nw:networks/nw:network/nw:node/l3t:l3-node-attributes" {
when "../../nw:network-types/l3t:l3-unicast-topology/" +
"ex-ospft:ospf" {
description
"Augments only for OSPF topology";
}
description
"Augments node configuration";
uses ospf-node-attributes;
}
augment "/nw:networks/nw:network/nt:link/l3t:l3-link-attributes" {
when "../../nw:network-types/l3t:l3-unicast-topology/" +
"ex-ospft:ospf" {
description
"Augments only for OSPF topology";
}

Clemm, et al. Standards Track [Page 27]

RFC 8346 YANG Data Model for L3 Topologies March 2018

description
"Augments link configuration";
uses ospf-link-attributes;
}
grouping ospf-node-attributes {
description
"OSPF node scope attributes";
container ospf-node-attributes {
description
"Contains 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
"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;

Clemm, et al. Standards Track [Page 28]

RFC 8346 YANG Data Model for L3 Topologies March 2018

default "0";
description
"For pseudonodes, DR interface-id";
}
}
}
grouping ospf-link-attributes {
description
"OSPF link scope attributes";
container ospf-link-attributes {
description
"Contains OSPF link attributes";
}
} // ospf-link-attributes
augment "/l3t:l3-node-event" {
description
"OSPF node event";
uses ospf-topology-type;
uses ospf-node-attributes;
}
augment "/l3t:l3-link-event" {
description
"OSPF link event";
uses ospf-topology-type;
uses ospf-link-attributes;
}
}

Appendix C. An Example

This section contains an example of an instance data tree in JSON
encoding [RFC7951]. The example instantiates "ietf-l3-unicast-
topology" for the topology that is depicted in the following diagram.
There are three nodes: D1, D2, and D3. D1 has three termination
points: 1-0-1, 1-2-1, and 1-3-1. D2 has three termination points as
well: 2-1-1, 2-0-1, and 2-3-1. D3 has two termination points: 3-1-1
and 3-2-1. In addition, there are six links, two between each pair
of nodes, with one going in each direction.

Clemm, et al. Standards Track [Page 29]

RFC 8346 YANG Data Model for L3 Topologies March 2018

+------------+ +------------+
| D1 | | D2 |
/-\ /-\ /-\ /-\
| | 1-0-1 | |---------------->| | 2-1-1 | |
| | 1-2-1 | |<----------------| | 2-0-1 | |
\-/ 1-3-1 \-/ \-/ 2-3-1 \-/
| /----\ | | /----\ |
+---| |---+ +---| |---+
\----/ \----/
A | A |
| | | |
| | | |
| | +------------+ | |
| | | D3 | | |
| | /-\ /-\ | |
| +----->| | 3-1-1 | |-------+ |
+---------| | 3-2-1 | |<---------+
\-/ \-/
| |
+------------+

Figure 2: A Network Topology Example

The corresponding instance data tree is depicted below. Note that
some lines have been wrapped to adhere to the 72-character line
limitation of RFCs.

{
"ietf-network:networks": {
"network": [
{
"network-types": {
"ietf-l3-unicast-topology:l3-unicast-topology": {}
},
"network-id": "l3-topo-example",
"node": [
{
"node-id": "D1",
"termination-point": [
{
"tp-id": "1-0-1",
"ietf-l3-unicast-topology:
l3-termination-point-attributes": {
"unnumbered-id:": 101
}
},
{
"tp-id": "1-2-1",

Clemm, et al. Standards Track [Page 30]

RFC 8346 YANG Data Model for L3 Topologies March 2018

"ietf-l3-unicast-topology:
l3-termination-point-attributes": {
"unnumbered-id:": 121
}
},
{
"tp-id": "1-3-1",
"ietf-l3-unicast-topology:
l3-termination-point-attributes": {
"unnumbered-id:": 131
}
}
],
"ietf-l3-unicast-topology:l3-node-attributes": {
"router-id": ["203.0.113.1"]
}
},
{
"node-id": "D2",
"termination-point": [
{
"tp-id": "2-0-1",
"ietf-l3-unicast-topology:
l3-termination-point-attributes": {
"unnumbered-id:": 201
}
},
{
"tp-id": "2-1-1",
"ietf-l3-unicast-topology:
l3-termination-point-attributes": {
"unnumbered-id:": 211
}
},
{
"tp-id": "2-3-1",
"ietf-l3-unicast-topology:
l3-termination-point-attributes": {
"unnumbered-id:": 231
}
}
],
"ietf-l3-unicast-topology:l3-node-attributes": {
"router-id": ["203.0.113.2"]
}
},
{
"node-id": "D3",

Clemm, et al. Standards Track [Page 31]

RFC 8346 YANG Data Model for L3 Topologies March 2018

"termination-point": [
{
"tp-id": "3-1-1",
"ietf-l3-unicast-topology:
l3-termination-point-attributes": {
"unnumbered-id:": 311
}
},
{
"tp-id": "3-2-1",
"ietf-l3-unicast-topology:
l3-termination-point-attributes": {
"unnumbered-id:": 321
}
}
],
"ietf-l3-unicast-topology:l3-node-attributes": {
"router-id": ["203.0.113.3"]
}
}
],
"ietf-network-topology:link": [
{
"link-id": "D1,1-2-1,D2,2-1-1",
"source": {
"source-node": "D1",
"source-tp": "1-2-1"
}
"destination": {
"dest-node": "D2",
"dest-tp": "2-1-1"
},
"ietf-l3-unicast-topology:l3-link-attributes": {
"metric1": "100"
}
},
{
"link-id": "D2,2-1-1,D1,1-2-1",
"source": {
"source-node": "D2",
"source-tp": "2-1-1"
}
"destination": {
"dest-node": "D1",
"dest-tp": "1-2-1"
},
"ietf-l3-unicast-topology:l3-link-attributes": {
"metric1": "100"

Clemm, et al. Standards Track [Page 32]

RFC 8346 YANG Data Model for L3 Topologies March 2018

}
},
{
"link-id": "D1,1-3-1,D3,3-1-1",
"source": {
"source-node": "D1",
"source-tp": "1-3-1"
}
"destination": {
"dest-node": "D3",
"dest-tp": "3-1-1"
},
"ietf-l3-unicast-topology:l3-link-attributes": {
"metric1": "100"
}
},
{
"link-id": "D3,3-1-1,D1,1-3-1",
"source": {
"source-node": "D3",
"source-tp": "3-1-1"
}
"destination": {
"dest-node": "D1",
"dest-tp": "1-3-1"
},
"ietf-l3-unicast-topology:l3-link-attributes": {
"metric1": "100"
}
},
{
"link-id": "D2,2-3-1,D3,3-2-1",
"source": {
"source-node": "D2",
"source-tp": "2-3-1"
}
"destination": {
"dest-node": "D3",
"dest-tp": "3-2-1"
},
"ietf-l3-unicast-topology:l3-link-attributes": {
"metric1": "100"
}
},
{
"link-id": "D3,3-2-1,D2,2-3-1",
"source": {
"source-node": "D3",

Clemm, et al. Standards Track [Page 33]

RFC 8346 YANG Data Model for L3 Topologies March 2018

"source-tp": "3-2-1"
}
"destination": {
"dest-node": "D2",
"dest-tp": "2-3-1"
},
"ietf-l3-unicast-topology:l3-link-attributes": {
"metric1": "100"
}
}
]
}
]
}
}

Figure 3: Instance Data Tree

Acknowledgments

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, Michal Vasco, and Kent
Watsen.

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

Clemm, et al. Standards Track [Page 34]

RFC 8346 YANG Data Model for L3 Topologies March 2018

Authors' Addresses

Alexander Clemm
Huawei USA - Futurewei Technologies Inc.
Santa Clara, CA
United States of America

Email: [email protected], [email protected]

Jan Medved
Cisco

Email: [email protected]

Robert Varga
Pantheon Technologies SRO

Email: [email protected]

Xufeng Liu
Jabil

Email: [email protected]

Hariharan Ananthakrishnan
Packet Design

Email: [email protected]

Nitin Bahadur
Bracket Computing

Email: [email protected]

Clemm, et al. Standards Track [Page 35]