Internet Engineering Task Force (IETF)                         L. Lhotka
Request for Comments: 8022                                        CZ.NIC
Category: Standards Track                                      A. Lindem
ISSN: 2070-1721                                            Cisco Systems
                                                           November 2016

A YANG Data Model for Routing Management

Abstract

   This document contains a specification of three YANG modules and one
   submodule.  Together they form the core routing data model that
   serves as a framework for configuring and managing a routing
   subsystem.  It is expected that these modules will be augmented by
   additional YANG modules defining data models for control-plane
   protocols, route filters, and other functions.  The core routing data
   model provides common building blocks for such extensions -- routes,
   Routing Information Bases (RIBs), and control-plane protocols.

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
   http://www.rfc-editor.org/info/rfc8022.

Copyright Notice

   Copyright (c) 2016 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) 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.

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology and Notation  . . . . . . . . . . . . . . . . . .   3
     2.1.  Glossary of New Terms . . . . . . . . . . . . . . . . . .   4
     2.2.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Prefixes in Data Node Names . . . . . . . . . . . . . . .   5
   3.  Objectives  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  The Design of the Core Routing Data Model . . . . . . . . . .   6
     4.1.  System-Controlled and User-Controlled List Entries  . . .   8
   5.  Basic Building Blocks . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Route . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.2.  Routing Information Base (RIB)  . . . . . . . . . . . . .   9
     5.3.  Control-Plane Protocol  . . . . . . . . . . . . . . . . .  10
       5.3.1.  Routing Pseudo-Protocols  . . . . . . . . . . . . . .  10
       5.3.2.  Defining New Control-Plane Protocols  . . . . . . . .  11
     5.4.  Parameters of IPv6 Router Advertisements  . . . . . . . .  12
   6.  Interactions with Other YANG Modules  . . . . . . . . . . . .  13
     6.1.  Module "ietf-interfaces"  . . . . . . . . . . . . . . . .  13
     6.2.  Module "ietf-ip"  . . . . . . . . . . . . . . . . . . . .  13
   7.  Routing Management YANG Module  . . . . . . . . . . . . . . .  14
   8.  IPv4 Unicast Routing Management YANG Module . . . . . . . . .  26
   9.  IPv6 Unicast Routing Management YANG Module . . . . . . . . .  32
     9.1.  IPv6 Router Advertisements Submodule  . . . . . . . . . .  37
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  47
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  48
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  49
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  49
     12.2.  Informative References . . . . . . . . . . . . . . . . .  50
   Appendix A.  The Complete Data Trees  . . . . . . . . . . . . . .  51
     A.1.  Configuration Data  . . . . . . . . . . . . . . . . . . .  51
     A.2.  State Data  . . . . . . . . . . . . . . . . . . . . . . .  52
   Appendix B.  Minimum Implementation . . . . . . . . . . . . . . .  53
   Appendix C.  Example: Adding a New Control-Plane Protocol . . . .  54
   Appendix D.  Data Tree Example  . . . . . . . . . . . . . . . . .  56
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  64
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  64

1. Introduction

   This document contains a specification of the following YANG modules:

   o  The "ietf-routing" module provides generic components of a routing
      data model.

   o  The "ietf-ipv4-unicast-routing" module augments the "ietf-routing"
      module with additional data specific to IPv4 unicast.

   o  The "ietf-ipv6-unicast-routing" module augments the "ietf-routing"
      module with additional data specific to IPv6 unicast.  Its
      submodule "ietf-ipv6-router-advertisements" also augments the
      "ietf-interfaces" [RFC7223] and "ietf-ip" [RFC7277] modules with
      IPv6 router configuration variables required by [RFC4861].

   These modules together define the so-called core routing data model,
   which is intended as a basis for future data model development
   covering more-sophisticated routing systems.  While these three
   modules can be directly used for simple IP devices with static
   routing (see Appendix B), their main purpose is to provide essential
   building blocks for more-complicated data models involving multiple
   control-plane protocols, multicast routing, additional address
   families, and advanced functions such as route filtering or policy
   routing.  To this end, it is expected that the core routing data
   model will be augmented by numerous modules developed by various IETF
   working groups.

2. Terminology and Notation

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

   The following terms are defined in [RFC6241]:

   o  client

   o  message

   o  protocol operation

   o  server

   The following terms are defined in [RFC7950]:

   o  action

   o  augment

   o  configuration data

   o  container

   o  container with presence

   o  data model

   o  data node

   o  feature

   o  leaf

   o  list

   o  mandatory node

   o  module

   o  schema tree

   o  state data

   o  RPC (Remote Procedure Call) operation

2.1. Glossary of New Terms

   core routing data model:  YANG data model comprising "ietf-routing",
      "ietf-ipv4-unicast-routing", and "ietf-ipv6-unicast-routing"
      modules.

   direct route:  a route to a directly connected network.

   Routing Information Base (RIB):  An object containing a list of
      routes together with other information.  See Section 5.2 for
      details.

   system-controlled entry:  An entry of a list in state data ("config
      false") that is created by the system independently of what has
      been explicitly configured.  See Section 4.1 for details.

   user-controlled entry:  An entry of a list in state data ("config
      false") that is created and deleted as a direct consequence of
      certain configuration changes.  See Section 4.1 for details.

2.2. Tree Diagrams

   A simplified graphical representation of the complete data tree is
   presented in Appendix A, and similar diagrams of its various subtrees
   appear in the main text.

   o  Brackets "[" and "]" enclose list keys.

   o  Curly braces "{" and "}" contain names of optional features that
      make the corresponding node conditional.

   o  Abbreviations before data node names: "rw" means configuration
      (read-write), "ro" state data (read-only), "-x" RPC operations or
      actions, and "-n" notifications.

   o  Symbols after data node names: "?" means an optional node, "!" a
      container with presence, and "*" denotes a "list" or "leaf-list".

   o  Parentheses enclose choice and case nodes, and case nodes are also
      marked with a colon (":").

   o  Ellipsis ("...") stands for contents of subtrees that are not
      shown.

2.3. Prefixes in Data Node Names

3. Objectives

   The initial design of the core routing data model was driven by the
   following objectives:

   o  The data model should be suitable for the common address families
      -- in particular, IPv4 and IPv6 -- and for unicast and multicast
      routing, as well as Multiprotocol Label Switching (MPLS).

   o  A simple IP routing system, such as one that uses only static
      routing, should be configurable in a simple way, ideally without
      any need to develop additional YANG modules.

   o  On the other hand, the core routing framework must allow for
      complicated implementations involving multiple Routing Information
      Bases (RIBs) and multiple control-plane protocols, as well as
      controlled redistributions of routing information.

   o  Because device vendors will want to map the data models built on
      this generic framework to their proprietary data models and
      configuration interfaces, the framework should be flexible enough
      to facilitate that and accommodate data models with different
      logic.

4. The Design of the Core Routing Data Model

   The core routing data model consists of three YANG modules and one
   submodule.  The first module, "ietf-routing", defines the generic
   components of a routing system.  The other two modules, "ietf-ipv4-
   unicast-routing" and "ietf-ipv6-unicast-routing", augment the "ietf-
   routing" module with additional data nodes that are needed for IPv4
   and IPv6 unicast routing, respectively.  The "ietf-ipv6-unicast-
   routing" module has a submodule, "ietf-ipv6-router-advertisements",
   that augments the "ietf-interfaces" [RFC7223] and "ietf-ip" [RFC7277]
   modules with configuration variables for IPv6 router advertisements
   as required by [RFC4861].  Figures 1 and 2 show abridged views of the
   configuration and state data hierarchies.  See Appendix A for the
   complete data trees.

   +--rw routing
      +--rw router-id?
      +--rw control-plane-protocols
      |  +--rw control-plane-protocol* [type name]
      |     +--rw type
      |     +--rw name
      |     +--rw description?
      |     +--rw static-routes
      |        +--rw v6ur:ipv6
      |        |     ...
      |        +--rw v4ur:ipv4
      |              ...
      +--rw ribs
         +--rw rib* [name]
            +--rw name
            +--rw address-family?
            +--rw description?

                  Figure 1: Configuration Data Hierarchy

   +--ro routing-state
      +--ro router-id?
      +--ro interfaces
      |  +--ro interface*
      +--ro control-plane-protocols
      |  +--ro control-plane-protocol* [type name]
      |     +--ro type
      |     +--ro name
      +--ro ribs
         +--ro rib* [name]
            +--ro name
            +--ro address-family
            +--ro default-rib?
            +--ro routes
            |  +--ro route*
            |        ...

                      Figure 2: State Data Hierarchy

   As can be seen from Figures 1 and 2, the core routing data model
   introduces several generic components of a routing framework: routes,
   RIBs containing lists of routes, and control-plane protocols.
   Section 5 describes these components in more detail.

4.1. System-Controlled and User-Controlled List Entries

   The core routing data model defines several lists in the schema tree,
   such as "rib", that have to be populated with at least one entry in
   any properly functioning device, and additional entries may be
   configured by a client.

   In such a list, the server creates the required item as a so-called
   system-controlled entry in state data, i.e., inside the "routing-
   state" container.

   An example can be seen in Appendix D: the "/routing-state/ribs/rib"
   list has two system-controlled entries named "ipv4-master" and
   "ipv6-master".

   Additional entries may be created in the configuration by a client,
   e.g., via the NETCONF protocol.  These are so-called user-controlled
   entries.  If the server accepts a configured user-controlled entry,
   then this entry also appears in the state data version of the list.

   Corresponding entries in both versions of the list (in state data and
   configuration) have the same value of the list key.

   A client may also provide supplemental configuration of system-
   controlled entries.  To do so, the client creates a new entry in the
   configuration with the desired contents.  In order to bind this entry
   to the corresponding entry in the state data list, the key of the
   configuration entry has to be set to the same value as the key of the
   state entry.

   Deleting a user-controlled entry from the configuration list results
   in the removal of the corresponding entry in the state data list.  In
   contrast, if a system-controlled entry is deleted from the
   configuration list, only the extra configuration specified in that
   entry is removed but the corresponding state data entry remains in
   the list.

5. Basic Building Blocks

This section describes the essential components of the core routing
data model.

5.1. Route

   Routes are basic elements of information in a routing system.  The
   core routing data model defines only the following minimal set of
   route attributes:

   o  "destination-prefix": address prefix specifying the set of
      destination addresses for which the route may be used.  This
      attribute is mandatory.

   o  "route-preference": an integer value (also known as administrative
      distance) that is used for selecting a preferred route among
      routes with the same destination prefix.  A lower value means a
      more preferred route.

   o  "next-hop": determines the outgoing interface and/or next-hop
      address(es), or a special operation to be performed with a packet.

   Routes are primarily state data that appear as entries of RIBs
   (Section 5.2) but they may also be found in configuration data, for
   example, as manually configured static routes.  In the latter case,
   configurable route attributes are generally a subset of attributes
   defined for RIB routes.

5.2. Routing Information Base (RIB)

   Every implementation of the core routing data model manages one or
   more Routing Information Bases (RIBs).  A RIB is a list of routes
   complemented with administrative data.  Each RIB contains only routes
   of one address family.  An address family is represented by an
   identity derived from the "rt:address-family" base identity.

   In the core routing data model, RIBs are state data represented as
   entries of the list "/routing-state/ribs/rib".  The contents of RIBs
   are controlled and manipulated by control-plane protocol operations
   that may result in route additions, removals, and modifications.
   This also includes manipulations via the "static" and/or "direct"
   pseudo-protocols; see Section 5.3.1.

   For every supported address family, exactly one RIB MUST be marked as
   the so-called default RIB to which control-plane protocols place
   their routes by default.

   Simple router implementations that do not advertise the feature
   "multiple-ribs" will typically create one system-controlled RIB per
   supported address family and mark it as the default RIB.

   More-complex router implementations advertising the "multiple-ribs"
   feature support multiple RIBs per address family that can be used for
   policy routing and other purposes.

   The following action (see Section 7.15 of [RFC7950]) is defined for
   the "rib" list:

   o  active-route -- return the active RIB route for the destination
      address that is specified as the action's input parameter.

5.3. Control-Plane Protocol

   The core routing data model provides an open-ended framework for
   defining multiple control-plane protocol instances, e.g., for Layer 3
   routing protocols.  Each control-plane protocol instance MUST be
   assigned a type, which is an identity derived from the
   "rt:control-plane-protocol" base identity.  The core routing data
   model defines two identities for the direct and static pseudo-
   protocols (Section 5.3.1).

   Multiple control-plane protocol instances of the same type MAY be
   configured.

5.3.1. Routing Pseudo-Protocols

   The core routing data model defines two special routing protocol
   types -- "direct" and "static".  Both are in fact pseudo-protocols,
   which means that they are confined to the local device and do not
   exchange any routing information with adjacent routers.

   Every implementation of the core routing data model MUST provide
   exactly one instance of the "direct" pseudo-protocol type.  It is the
   source of direct routes for all configured address families.  Direct
   routes are normally supplied by the operating system kernel, based on
   the configuration of network interface addresses; see Section 6.2.

   A pseudo-protocol of the type "static" allows for specifying routes
   manually.  It MAY be configured in zero or multiple instances,
   although a typical configuration will have exactly one instance.

5.3.2. Defining New Control-Plane Protocols

   It is expected that future YANG modules will create data models for
   additional control-plane protocol types.  Such a new module has to
   define the protocol-specific configuration and state data, and it has
   to integrate it into the core routing framework in the following way:

   o  A new identity MUST be defined for the control-plane protocol, and
      its base identity MUST be set to "rt:control-plane-protocol" or to
      an identity derived from "rt:control-plane-protocol".

   o  Additional route attributes MAY be defined, preferably in one
      place by means of defining a YANG grouping.  The new attributes
      have to be inserted by augmenting the definitions of the nodes

       /rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route

      and

       /rt:routing-state/rt:ribs/rt:rib/rt:output/rt:route,

      and possibly other places in the configuration, state data,
      notifications, and input/output parameters of actions or RPC
      operations.

   o  Configuration parameters and/or state data for the new protocol
      can be defined by augmenting the "control-plane-protocol" data
      node under both "/routing" and "/routing-state".

   By using a "when" statement, the augmented configuration parameters
   and state data specific to the new protocol SHOULD be made
   conditional and valid only if the value of "rt:type" or
   "rt:source-protocol" is equal to (or derived from) the new protocol's
   identity.

   It is also RECOMMENDED that protocol-specific data nodes be
   encapsulated in an appropriately named container with presence.  Such
   a container may contain mandatory data nodes that are otherwise
   forbidden at the top level of an augment.

   The above steps are implemented by the example YANG module for the
   Routing Information Protocol (RIP) in Appendix C.

5.4. Parameters of IPv6 Router Advertisements

   YANG module "ietf-ipv6-router-advertisements" (Section 9.1), which is
   a submodule of the "ietf-ipv6-unicast-routing" module, augments the
   configuration and state data of IPv6 interfaces with definitions of
   the following variables as required by Section 6.2.1 of [RFC4861]:

   o  send-advertisements

   o  max-rtr-adv-interval

   o  min-rtr-adv-interval

   o  managed-flag

   o  other-config-flag

   o  link-mtu

   o  reachable-time

   o  retrans-timer

   o  cur-hop-limit

   o  default-lifetime

   o  prefix-list: a list of prefixes to be advertised.

      The following parameters are associated with each prefix in the
      list:

      *  valid-lifetime

      *  on-link-flag

      *  preferred-lifetime

      *  autonomous-flag

   NOTES:

   1.  The "IsRouter" flag, which is also required by [RFC4861], is
       implemented in the "ietf-ip" module [RFC7277] (leaf
       "ip:forwarding").

   2.  The original specification [RFC4861] allows the implementations
       to decide whether the "valid-lifetime" and "preferred-lifetime"
       parameters remain the same in consecutive advertisements or
       decrement in real time.  However, the latter behavior seems
       problematic because the values might be reset again to the
       (higher) configured values after a configuration is reloaded.
       Moreover, no implementation is known to use the decrementing
       behavior.  The "ietf-ipv6-router-advertisements" submodule
       therefore stipulates the former behavior with constant values.

6. Interactions with Other YANG Modules

The semantics of the core routing data model also depends on several
configuration parameters that are defined in other YANG modules.

6.1. Module "ietf-interfaces"

   The following boolean switch is defined in the "ietf-interfaces" YANG
   module [RFC7223]:

   /if:interfaces/if:interface/if:enabled

      If this switch is set to "false" for a network-layer interface,
      then all routing and forwarding functions MUST be disabled on this
      interface.

6.2. Module "ietf-ip"

   The following boolean switches are defined in the "ietf-ip" YANG
   module [RFC7277]:

   /if:interfaces/if:interface/ip:ipv4/ip:enabled

      If this switch is set to "false" for a network-layer interface,
      then all IPv4 routing and forwarding functions MUST be disabled on
      this interface.

   /if:interfaces/if:interface/ip:ipv4/ip:forwarding

      If this switch is set to "false" for a network-layer interface,
      then the forwarding of IPv4 datagrams through this interface MUST
      be disabled.  However, the interface MAY participate in other IPv4
      routing functions, such as routing protocols.

   /if:interfaces/if:interface/ip:ipv6/ip:enabled

      If this switch is set to "false" for a network-layer interface,
      then all IPv6 routing and forwarding functions MUST be disabled on
      this interface.

   /if:interfaces/if:interface/ip:ipv6/ip:forwarding

      If this switch is set to "false" for a network-layer interface,
      then the forwarding of IPv6 datagrams through this interface MUST
      be disabled.  However, the interface MAY participate in other IPv6
      routing functions, such as routing protocols.

   In addition, the "ietf-ip" module allows for configuring IPv4 and
   IPv6 addresses and network prefixes or masks on network-layer
   interfaces.  Configuration of these parameters on an enabled
   interface MUST result in an immediate creation of the corresponding
   direct route.  The destination prefix of this route is set according
   to the configured IP address and network prefix/mask, and the
   interface is set as the outgoing interface for that route.

7. Routing Management YANG Module

   <CODE BEGINS> file "ietf-routing@2016-11-04.yang"

   module ietf-routing {

     yang-version "1.1";

     namespace "urn:ietf:params:xml:ns:yang:ietf-routing";

     prefix "rt";

     import ietf-yang-types {
       prefix "yang";
     }

     import ietf-interfaces {
       prefix "if";
     }

     organization
       "IETF NETMOD (NETCONF Data Modeling Language) Working Group";

     contact
       "WG Web:   <https://datatracker.ietf.org/wg/netmod/>
        WG List:  <mailto:netmod@ietf.org>

        WG Chair: Lou Berger
                  <mailto:lberger@labn.net>

        WG Chair: Kent Watsen
                  <mailto:kwatsen@juniper.net>

        Editor:   Ladislav Lhotka
                  <mailto:lhotka@nic.cz>

        Editor:   Acee Lindem
                  <mailto:acee@cisco.com>";

     description
       "This YANG module defines essential components for the management
        of a routing subsystem.

        Copyright (c) 2016 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).

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
        'OPTIONAL' in the module text are to be interpreted as described
        in RFC 2119.

        This version of this YANG module is part of RFC 8022;
        see the RFC itself for full legal notices.";

     revision 2016-11-04 {
       description
         "Initial revision.";
       reference
         "RFC 8022: A YANG Data Model for Routing Management";
     }

     /* Features */

     feature multiple-ribs {
       description
         "This feature indicates that the server supports user-defined
          RIBs.

          Servers that do not advertise this feature SHOULD provide
          exactly one system-controlled RIB per supported address family
          and make it also the default RIB.  This RIB then appears as an
          entry of the list /routing-state/ribs/rib.";
     }

     feature router-id {
       description
         "This feature indicates that the server supports configuration
          of an explicit 32-bit router ID that is used by some routing
          protocols.

          Servers that do not advertise this feature set a router ID
          algorithmically, usually to one of the configured IPv4
          addresses.  However, this algorithm is implementation
          specific.";
     }

     /* Identities */

     identity address-family {
       description
         "Base identity from which identities describing address
          families are derived.";
     }

     identity ipv4 {
       base address-family;
       description
         "This identity represents IPv4 address family.";
     }

     identity ipv6 {
       base address-family;
       description
         "This identity represents IPv6 address family.";
     }

     identity control-plane-protocol {
       description
         "Base identity from which control-plane protocol identities are
          derived.";
     }

     identity routing-protocol {
       base control-plane-protocol;
       description
         "Identity from which Layer 3 routing protocol identities are

          derived.";
     }

     identity direct {
       base routing-protocol;
       description
         "Routing pseudo-protocol that provides routes to directly
          connected networks.";
     }

     identity static {
       base routing-protocol;
       description
         "Static routing pseudo-protocol.";
     }

     /* Type Definitions */

     typedef route-preference {
       type uint32;
       description
         "This type is used for route preferences.";
     }

     /* Groupings */

     grouping address-family {
       description
         "This grouping provides a leaf identifying an address
          family.";
       leaf address-family {
         type identityref {
           base address-family;
         }
         mandatory "true";
         description
           "Address family.";
       }
     }

     grouping router-id {
       description
         "This grouping provides router ID.";
       leaf router-id {
         type yang:dotted-quad;
         description
           "A 32-bit number in the form of a dotted quad that is used by
            some routing protocols identifying a router.";

         reference
           "RFC 2328: OSPF Version 2.";
       }
     }

     grouping special-next-hop {
       description
         "This grouping provides a leaf with an enumeration of special
          next hops.";
       leaf special-next-hop {
         type enumeration {
           enum blackhole {
             description
               "Silently discard the packet.";
           }
           enum unreachable {
             description
               "Discard the packet and notify the sender with an error
                message indicating that the destination host is
                unreachable.";
           }
           enum prohibit {
             description
               "Discard the packet and notify the sender with an error
                message indicating that the communication is
                administratively prohibited.";
           }
           enum receive {
             description
               "The packet will be received by the local system.";
           }
         }
         description
           "Options for special next hops.";
       }
     }

     grouping next-hop-content {
       description
         "Generic parameters of next hops in static routes.";
       choice next-hop-options {
         mandatory "true";
         description
           "Options for next hops in static routes.

            It is expected that further cases will be added through
            augments from other modules.";
         case simple-next-hop {

           description
             "This case represents a simple next hop consisting of the
              next-hop address and/or outgoing interface.

              Modules for address families MUST augment this case with a
              leaf containing a next-hop address of that address
              family.";
           leaf outgoing-interface {
             type if:interface-ref;
             description
               "Name of the outgoing interface.";
           }
         }
         case special-next-hop {
           uses special-next-hop;
         }
         case next-hop-list {
           container next-hop-list {
             description
               "Container for multiple next-hops.";
             list next-hop {
               key "index";
               description
                 "An entry of a next-hop list.

                  Modules for address families MUST augment this list
                  with a leaf containing a next-hop address of that
                  address family.";
               leaf index {
                 type string;
                 description
                   "A user-specified identifier utilized to uniquely
                    reference the next-hop entry in the next-hop list.
                    The value of this index has no semantic meaning
                    other than for referencing the entry.";
               }
               leaf outgoing-interface {
                 type if:interface-ref;
                 description
                   "Name of the outgoing interface.";
               }
             }
           }
         }
       }
     }

     grouping next-hop-state-content {
       description
         "Generic parameters of next hops in state data.";
       choice next-hop-options {
         mandatory "true";
         description
           "Options for next hops in state data.

            It is expected that further cases will be added through
            augments from other modules, e.g., for recursive
            next hops.";
         case simple-next-hop {
           description
             "This case represents a simple next hop consisting of the
              next-hop address and/or outgoing interface.

              Modules for address families MUST augment this case with a
              leaf containing a next-hop address of that address
              family.";
           leaf outgoing-interface {
             type if:interface-state-ref;
             description
               "Name of the outgoing interface.";
           }
         }
         case special-next-hop {
           uses special-next-hop;
         }
         case next-hop-list {
           container next-hop-list {
             description
               "Container for multiple next hops.";
             list next-hop {
               description
                 "An entry of a next-hop list.

                  Modules for address families MUST augment this list
                  with a leaf containing a next-hop address of that
                  address family.";
               leaf outgoing-interface {
                 type if:interface-state-ref;
                 description
                   "Name of the outgoing interface.";
               }
             }
           }
         }
       }

     }

     grouping route-metadata {
       description
         "Common route metadata.";
       leaf source-protocol {
         type identityref {
           base routing-protocol;
         }
         mandatory "true";
         description
           "Type of the routing protocol from which the route
            originated.";
       }
       leaf active {
         type empty;
         description
           "Presence of this leaf indicates that the route is preferred
            among all routes in the same RIB that have the same
            destination prefix.";
       }
       leaf last-updated {
         type yang:date-and-time;
         description
           "Time stamp of the last modification of the route.  If the
            route was never modified, it is the time when the route was
            inserted into the RIB.";
       }
     }

     /* State data */

     container routing-state {
       config "false";
       description
         "State data of the routing subsystem.";
       uses router-id {
         description
           "Global router ID.

            It may be either configured or assigned algorithmically by
            the implementation.";
       }
       container interfaces {
         description
           "Network-layer interfaces used for routing.";
         leaf-list interface {
           type if:interface-state-ref;

           description
             "Each entry is a reference to the name of a configured
              network-layer interface.";
         }
       }
       container control-plane-protocols {
         description
           "Container for the list of routing protocol instances.";
         list control-plane-protocol {
           key "type name";
           description
             "State data of a control-plane protocol instance.

              An implementation MUST provide exactly one
              system-controlled instance of the 'direct'
              pseudo-protocol.  Instances of other control-plane
              protocols MAY be created by configuration.";
           leaf type {
             type identityref {
               base control-plane-protocol;
             }
             description
               "Type of the control-plane protocol.";
           }
           leaf name {
             type string;
             description
               "The name of the control-plane protocol instance.

                For system-controlled instances this name is persistent,
                i.e., it SHOULD NOT change across reboots.";
           }
         }
       }
       container ribs {
         description
           "Container for RIBs.";
         list rib {
           key "name";
           min-elements "1";
           description
             "Each entry represents a RIB identified by the 'name' key.
              All routes in a RIB MUST belong to the same address
              family.

              An implementation SHOULD provide one system-controlled
              default RIB for each supported address family.";
           leaf name {

             type string;
             description
               "The name of the RIB.";
           }
           uses address-family;
           leaf default-rib {
             if-feature "multiple-ribs";
             type boolean;
             default "true";
             description
               "This flag has the value of 'true' if and only if the RIB
                is the default RIB for the given address family.

                By default, control-plane protocols place their routes
                in the default RIBs.";
           }
           container routes {
             description
               "Current content of the RIB.";
             list route {
               description
                 "A RIB route entry.  This data node MUST be augmented
                  with information specific for routes of each address
                  family.";
               leaf route-preference {
                 type route-preference;
                 description
                   "This route attribute, also known as administrative
                    distance, allows for selecting the preferred route
                    among routes with the same destination prefix.  A
                    smaller value means a more preferred route.";
               }
               container next-hop {
                 description
                   "Route's next-hop attribute.";
                 uses next-hop-state-content;
               }
               uses route-metadata;
             }
           }
           action active-route {
             description
               "Return the active RIB route that is used for the
                destination address.

                Address-family-specific modules MUST augment input
                parameters with a leaf named 'destination-address'.";
             output {

               container route {
                 description
                   "The active RIB route for the specified destination.

                    If no route exists in the RIB for the destination
                    address, no output is returned.

                    Address-family-specific modules MUST augment this
                    container with appropriate route contents.";
                 container next-hop {
                   description
                     "Route's next-hop attribute.";
                   uses next-hop-state-content;
                 }
                 uses route-metadata;
               }
             }
           }
         }
       }
     }

     /* Configuration Data */

     container routing {
       description
         "Configuration parameters for the routing subsystem.";
       uses router-id {
         if-feature "router-id";
         description
           "Configuration of the global router ID.  Routing protocols
            that use router ID can use this parameter or override it
            with another value.";
       }
       container control-plane-protocols {
         description
           "Configuration of control-plane protocol instances.";
         list control-plane-protocol {
           key "type name";
           description
             "Each entry contains configuration of a control-plane
              protocol instance.";
           leaf type {
             type identityref {
               base control-plane-protocol;
             }
             description
               "Type of the control-plane protocol - an identity derived

                from the 'control-plane-protocol' base identity.";
           }
           leaf name {
             type string;
             description
               "An arbitrary name of the control-plane protocol
                instance.";
           }
           leaf description {
             type string;
             description
               "Textual description of the control-plane protocol
                instance.";
           }
           container static-routes {
             when "derived-from-or-self(../type, 'rt:static')" {
               description
                 "This container is only valid for the 'static' routing
                  protocol.";
             }
             description
               "Configuration of the 'static' pseudo-protocol.

                Address-family-specific modules augment this node with
                their lists of routes.";
           }
         }
       }
       container ribs {
         description
           "Configuration of RIBs.";
         list rib {
           key "name";
           description
             "Each entry contains configuration for a RIB identified by
              the 'name' key.

              Entries having the same key as a system-controlled entry
              of the list /routing-state/ribs/rib are used for
              configuring parameters of that entry.  Other entries
              define additional user-controlled RIBs.";
           leaf name {
             type string;
             description
               "The name of the RIB.

                For system-controlled entries, the value of this leaf
                must be the same as the name of the corresponding entry

                in state data.

                For user-controlled entries, an arbitrary name can be
                used.";
           }
           uses address-family {
             description
               "Address family of the RIB.

                It is mandatory for user-controlled RIBs.  For
                system-controlled RIBs it can be omitted; otherwise, it
                must match the address family of the corresponding state
                entry.";
             refine "address-family" {
               mandatory "false";
             }
           }
           leaf description {
             type string;
             description
               "Textual description of the RIB.";
           }
         }
       }
     }
   }

   <CODE ENDS>

8. IPv4 Unicast Routing Management YANG Module

   <CODE BEGINS> file "ietf-ipv4-unicast-routing@2016-11-04.yang"

   module ietf-ipv4-unicast-routing {

     yang-version "1.1";

     namespace "urn:ietf:params:xml:ns:yang:ietf-ipv4-unicast-routing";

     prefix "v4ur";

     import ietf-routing {
       prefix "rt";
     }

     import ietf-inet-types {
       prefix "inet";
     }

     organization
       "IETF NETMOD (NETCONF Data Modeling Language) Working Group";

     contact
       "WG Web:   <https://datatracker.ietf.org/wg/netmod/>
        WG List:  <mailto:netmod@ietf.org>

        WG Chair: Lou Berger
                  <mailto:lberger@labn.net>

        WG Chair: Kent Watsen
                  <mailto:kwatsen@juniper.net>

        Editor:   Ladislav Lhotka
                  <mailto:lhotka@nic.cz>

        Editor:   Acee Lindem
                  <mailto:acee@cisco.com>";

     description
       "This YANG module augments the 'ietf-routing' module with basic
        configuration and state data for IPv4 unicast routing.

        Copyright (c) 2016 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).

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
        'OPTIONAL' in the module text are to be interpreted as described
        in RFC 2119.

        This version of this YANG module is part of RFC 8022;
        see the RFC itself for full legal notices.";

     revision 2016-11-04 {
       description
         "Initial revision.";
       reference
         "RFC 8022: A YANG Data Model for Routing Management";
     }

     /* Identities */

     identity ipv4-unicast {
       base rt:ipv4;
       description
         "This identity represents the IPv4 unicast address family.";
     }

     /* State data */

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route" {
       when "derived-from-or-self(../../rt:address-family, "
          + "'v4ur:ipv4-unicast')" {
         description
           "This augment is valid only for IPv4 unicast.";
       }
       description
         "This leaf augments an IPv4 unicast route.";
       leaf destination-prefix {
         type inet:ipv4-prefix;
         description
           "IPv4 destination prefix.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route/"
           + "rt:next-hop/rt:next-hop-options/rt:simple-next-hop" {
       when "derived-from-or-self(../../../rt:address-family, "
          + "'v4ur:ipv4-unicast')" {
         description
           "This augment is valid only for IPv4 unicast.";
       }
       description
         "Augment 'simple-next-hop' case in IPv4 unicast routes.";
       leaf next-hop-address {
         type inet:ipv4-address;
         description
           "IPv4 address of the next hop.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route/"
           + "rt:next-hop/rt:next-hop-options/rt:next-hop-list/"
           + "rt:next-hop-list/rt:next-hop" {
       when "derived-from-or-self(../../../../../rt:address-family, "
          + "'v4ur:ipv4-unicast')" {
         description
           "This augment is valid only for IPv4 unicast.";

       }
       description
         "This leaf augments the 'next-hop-list' case of IPv4 unicast
          routes.";
       leaf address {
         type inet:ipv4-address;
         description
           "IPv4 address of the next-hop.";
       }
     }

     augment
       "/rt:routing-state/rt:ribs/rt:rib/rt:active-route/rt:input" {
       when "derived-from-or-self(../rt:address-family, "
          + "'v4ur:ipv4-unicast')" {
         description
           "This augment is valid only for IPv4 unicast RIBs.";
       }
       description
         "This augment adds the input parameter of the 'active-route'
          action.";
       leaf destination-address {
         type inet:ipv4-address;
         description
           "IPv4 destination address.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:active-route/"
           + "rt:output/rt:route" {
       when "derived-from-or-self(../../rt:address-family, "
          + "'v4ur:ipv4-unicast')" {
         description
           "This augment is valid only for IPv4 unicast.";
       }
       description
         "This augment adds the destination prefix to the reply of the
          'active-route' action.";
       leaf destination-prefix {
         type inet:ipv4-prefix;
         description
           "IPv4 destination prefix.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:active-route/"
           + "rt:output/rt:route/rt:next-hop/rt:next-hop-options/"
           + "rt:simple-next-hop" {

       when "derived-from-or-self(../../../rt:address-family, "
          + "'v4ur:ipv4-unicast')" {
         description
           "This augment is valid only for IPv4 unicast.";
       }
       description
         "Augment 'simple-next-hop' case in the reply to the
          'active-route' action.";
       leaf next-hop-address {
         type inet:ipv4-address;
         description
           "IPv4 address of the next hop.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:active-route/"
           + "rt:output/rt:route/rt:next-hop/rt:next-hop-options/"
           + "rt:next-hop-list/rt:next-hop-list/rt:next-hop" {
       when "derived-from-or-self(../../../../../rt:address-family, "
          + "'v4ur:ipv4-unicast')" {
         description
           "This augment is valid only for IPv4 unicast.";
       }
       description
         "Augment 'next-hop-list' case in the reply to the
          'active-route' action.";
       leaf next-hop-address {
         type inet:ipv4-address;
         description
           "IPv4 address of the next hop.";
       }
     }

     /* Configuration data */

     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/rt:static-routes" {
       description
         "This augment defines the configuration of the 'static'
          pseudo-protocol with data specific to IPv4 unicast.";
       container ipv4 {
         description
           "Configuration of a 'static' pseudo-protocol instance
            consists of a list of routes.";
         list route {
           key "destination-prefix";
           description
             "A list of static routes.";

           leaf destination-prefix {
             type inet:ipv4-prefix;
             mandatory "true";
             description
               "IPv4 destination prefix.";
           }
           leaf description {
             type string;
             description
               "Textual description of the route.";
           }
           container next-hop {
             description
               "Configuration of next-hop.";
             uses rt:next-hop-content {
               augment "next-hop-options/simple-next-hop" {
                 description
                   "Augment 'simple-next-hop' case in IPv4 static
                    routes.";
                 leaf next-hop-address {
                   type inet:ipv4-address;
                   description
                     "IPv4 address of the next hop.";
                 }
               }
               augment "next-hop-options/next-hop-list/next-hop-list/"
                     + "next-hop" {
                 description
                   "Augment 'next-hop-list' case in IPv4 static
                    routes.";
                 leaf next-hop-address {
                   type inet:ipv4-address;
                   description
                     "IPv4 address of the next hop.";
                 }
               }
             }
           }
         }
       }
     }
   }

   <CODE ENDS>

9. IPv6 Unicast Routing Management YANG Module

   <CODE BEGINS> file "ietf-ipv6-unicast-routing@2016-11-04.yang"

   module ietf-ipv6-unicast-routing {

     yang-version "1.1";

     namespace "urn:ietf:params:xml:ns:yang:ietf-ipv6-unicast-routing";

     prefix "v6ur";

     import ietf-routing {
       prefix "rt";
     }

     import ietf-inet-types {
       prefix "inet";
     }

     include ietf-ipv6-router-advertisements {
       revision-date 2016-11-04;
     }

     organization
       "IETF NETMOD (NETCONF Data Modeling Language) Working Group";

     contact
       "WG Web:   <https://datatracker.ietf.org/wg/netmod/>
        WG List:  <mailto:netmod@ietf.org>

        WG Chair: Lou Berger
                  <mailto:lberger@labn.net>

        WG Chair: Kent Watsen
                  <mailto:kwatsen@juniper.net>

        Editor:   Ladislav Lhotka
                  <mailto:lhotka@nic.cz>

        Editor:   Acee Lindem
                  <mailto:acee@cisco.com>";

     description
       "This YANG module augments the 'ietf-routing' module with basic
        configuration and state data for IPv6 unicast routing.

        Copyright (c) 2016 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).

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
        'OPTIONAL' in the module text are to be interpreted as described
        in RFC 2119.

        This version of this YANG module is part of RFC 8022;
        see the RFC itself for full legal notices.";

     revision 2016-11-04 {
       description
         "Initial revision.";
       reference
         "RFC 8022: A YANG Data Model for Routing Management";
     }

     /* Identities */

     identity ipv6-unicast {
       base rt:ipv6;
       description
         "This identity represents the IPv6 unicast address family.";
     }

     /* State data */

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route" {
       when "derived-from-or-self(../../rt:address-family, "
          + "'v6ur:ipv6-unicast')" {
         description
           "This augment is valid only for IPv6 unicast.";
       }
       description
         "This leaf augments an IPv6 unicast route.";
       leaf destination-prefix {
         type inet:ipv6-prefix;
         description
           "IPv6 destination prefix.";
       }

     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route/"
           + "rt:next-hop/rt:next-hop-options/rt:simple-next-hop" {
       when "derived-from-or-self(../../../rt:address-family, "
          + "'v6ur:ipv6-unicast')" {
         description
           "This augment is valid only for IPv6 unicast.";
       }
       description
         "Augment 'simple-next-hop' case in IPv6 unicast routes.";
       leaf next-hop-address {
         type inet:ipv6-address;
         description
           "IPv6 address of the next hop.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route/"
           + "rt:next-hop/rt:next-hop-options/rt:next-hop-list/"
           + "rt:next-hop-list/rt:next-hop" {
       when "derived-from-or-self(../../../../../rt:address-family, "
          + "'v6ur:ipv6-unicast')" {
         description
           "This augment is valid only for IPv6 unicast.";
       }
       description
         "This leaf augments the 'next-hop-list' case of IPv6 unicast
          routes.";
       leaf address {
         type inet:ipv6-address;
         description
           "IPv6 address of the next hop.";
       }
     }

     augment
       "/rt:routing-state/rt:ribs/rt:rib/rt:active-route/rt:input" {
       when "derived-from-or-self(../rt:address-family, "
          + "'v6ur:ipv6-unicast')" {
         description
           "This augment is valid only for IPv6 unicast RIBs.";
       }
       description
         "This augment adds the input parameter of the 'active-route'
          action.";
       leaf destination-address {
         type inet:ipv6-address;

         description
           "IPv6 destination address.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:active-route/"
           + "rt:output/rt:route" {
       when "derived-from-or-self(../../rt:address-family, "
          + "'v6ur:ipv6-unicast')" {
         description
           "This augment is valid only for IPv6 unicast.";
       }
       description
         "This augment adds the destination prefix to the reply of the
          'active-route' action.";
       leaf destination-prefix {
         type inet:ipv6-prefix;
         description
           "IPv6 destination prefix.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:active-route/"
           + "rt:output/rt:route/rt:next-hop/rt:next-hop-options/"
           + "rt:simple-next-hop" {
       when "derived-from-or-self(../../../rt:address-family, "
          + "'v6ur:ipv6-unicast')" {
         description
           "This augment is valid only for IPv6 unicast.";
       }
       description
         "Augment 'simple-next-hop' case in the reply to the
          'active-route' action.";
       leaf next-hop-address {
         type inet:ipv6-address;
         description
           "IPv6 address of the next hop.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:active-route/"
           + "rt:output/rt:route/rt:next-hop/rt:next-hop-options/"
           + "rt:next-hop-list/rt:next-hop-list/rt:next-hop" {
       when "derived-from-or-self(../../../../../rt:address-family, "
          + "'v6ur:ipv6-unicast')" {
         description
           "This augment is valid only for IPv6 unicast.";
       }

       description
         "Augment 'next-hop-list' case in the reply to the
          'active-route' action.";
       leaf next-hop-address {
         type inet:ipv6-address;
         description
           "IPv6 address of the next hop.";
       }
     }

     /* Configuration data */

     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/rt:static-routes" {
       description
         "This augment defines the configuration of the 'static'
          pseudo-protocol with data specific to IPv6 unicast.";
       container ipv6 {
         description
           "Configuration of a 'static' pseudo-protocol instance
            consists of a list of routes.";
         list route {
           key "destination-prefix";
           description
             "A list of static routes.";
           leaf destination-prefix {
             type inet:ipv6-prefix;
             mandatory "true";
             description
               "IPv6 destination prefix.";
           }
           leaf description {
             type string;
             description
               "Textual description of the route.";
           }
           container next-hop {
             description
               "Configuration of next-hop.";
             uses rt:next-hop-content {
               augment "next-hop-options/simple-next-hop" {
                 description
                   "Augment 'simple-next-hop' case in IPv6 static
                    routes.";
                 leaf next-hop-address {
                   type inet:ipv6-address;
                   description
                     "IPv6 address of the next hop.";

                 }
               }
               augment "next-hop-options/next-hop-list/next-hop-list/"
                     + "next-hop" {
                 description
                   "Augment 'next-hop-list' case in IPv6 static
                    routes.";
                 leaf next-hop-address {
                   type inet:ipv6-address;
                   description
                     "IPv6 address of the next hop.";
                 }
               }
             }
           }
         }
       }
     }
   }

   <CODE ENDS>

9.1. IPv6 Router Advertisements Submodule

   <CODE BEGINS> file "ietf-ipv6-router-advertisements@2016-11-04.yang"

   submodule ietf-ipv6-router-advertisements {

     yang-version "1.1";

     belongs-to ietf-ipv6-unicast-routing {
       prefix "v6ur";
     }

     import ietf-inet-types {
       prefix "inet";
     }

     import ietf-interfaces {
       prefix "if";
     }

     import ietf-ip {
       prefix "ip";
     }

     organization
       "IETF NETMOD (NETCONF Data Modeling Language) Working Group";

     contact
       "WG Web:   <https://datatracker.ietf.org/wg/netmod/>
        WG List:  <mailto:netmod@ietf.org>

        WG Chair: Lou Berger
                  <mailto:lberger@labn.net>

        WG Chair: Kent Watsen
                  <mailto:kwatsen@juniper.net>

        Editor:   Ladislav Lhotka
                  <mailto:lhotka@nic.cz>

        Editor:   Acee Lindem
                  <mailto:acee@cisco.com>";

     description
       "This YANG module augments the 'ietf-ip' module with
        configuration and state data of IPv6 router advertisements.

        Copyright (c) 2016 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).

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
        'OPTIONAL' in the module text are to be interpreted as described
        in RFC 2119.

        This version of this YANG module is part of RFC 8022;
        see the RFC itself for full legal notices.";

     reference
       "RFC 4861: Neighbor Discovery for IP version 6 (IPv6).";

     revision 2016-11-04 {
       description
         "Initial revision.";
       reference
         "RFC 8022: A YANG Data Model for Routing Management";
     }

     /* State data */

     augment "/if:interfaces-state/if:interface/ip:ipv6" {
       description
         "Augment interface state data with parameters of IPv6 router
          advertisements.";
       container ipv6-router-advertisements {
         description
           "Parameters of IPv6 Router Advertisements.";
         leaf send-advertisements {
           type boolean;
           description
             "A flag indicating whether or not the router sends periodic
              Router Advertisements and responds to Router
              Solicitations.";
         }
         leaf max-rtr-adv-interval {
           type uint16 {
             range "4..1800";
           }
           units "seconds";
           description
             "The maximum time allowed between sending unsolicited
              multicast Router Advertisements from the interface.";
         }
         leaf min-rtr-adv-interval {
           type uint16 {
             range "3..1350";
           }
           units "seconds";
           description
             "The minimum time allowed between sending unsolicited
              multicast Router Advertisements from the interface.";
         }
         leaf managed-flag {
           type boolean;
           description
             "The value that is placed in the 'Managed address
              configuration' flag field in the Router Advertisement.";
         }
         leaf other-config-flag {
           type boolean;
           description
             "The value that is placed in the 'Other configuration' flag
              field in the Router Advertisement.";
         }
         leaf link-mtu {
           type uint32;

           description
             "The value that is placed in MTU options sent by the
              router.  A value of zero indicates that no MTU options are
              sent.";
         }
         leaf reachable-time {
           type uint32 {
             range "0..3600000";
           }
           units "milliseconds";
           description
             "The value that is placed in the Reachable Time field in
              the Router Advertisement messages sent by the router.  A
              value of zero means unspecified (by this router).";
         }
         leaf retrans-timer {
           type uint32;
           units "milliseconds";
           description
             "The value that is placed in the Retrans Timer field in the
              Router Advertisement messages sent by the router.  A value
              of zero means unspecified (by this router).";
         }

         leaf cur-hop-limit {
           type uint8;
           description
             "The value that is placed in the Cur Hop Limit field in the
              Router Advertisement messages sent by the router.  A value
              of zero means unspecified (by this router).";
         }
         leaf default-lifetime {
           type uint16 {
             range "0..9000";
           }
           units "seconds";
           description
             "The value that is placed in the Router Lifetime field of
              Router Advertisements sent from the interface, in seconds.
              A value of zero indicates that the router is not to be
              used as a default router.";
         }
         container prefix-list {
           description
             "A list of prefixes that are placed in Prefix Information
              options in Router Advertisement messages sent from the
              interface.

              By default, these are all prefixes that the router
              advertises via routing protocols as being on-link for the
              interface from which the advertisement is sent.";
           list prefix {
             key "prefix-spec";
             description
               "Advertised prefix entry and its parameters.";
             leaf prefix-spec {
               type inet:ipv6-prefix;
               description
                 "IPv6 address prefix.";
             }
             leaf valid-lifetime {
               type uint32;
               units "seconds";
               description
                 "The value that is placed in the Valid Lifetime in the
                  Prefix Information option.  The designated value of
                  all 1's (0xffffffff) represents infinity.

                  An implementation SHOULD keep this value constant in
                  consecutive advertisements except when it is
                  explicitly changed in configuration.";
             }
             leaf on-link-flag {
               type boolean;
               description
                 "The value that is placed in the on-link flag ('L-bit')
                  field in the Prefix Information option.";
             }
             leaf preferred-lifetime {
               type uint32;
               units "seconds";
               description
                 "The value that is placed in the Preferred Lifetime in
                  the Prefix Information option, in seconds.  The
                  designated value of all 1's (0xffffffff) represents
                  infinity.

                  An implementation SHOULD keep this value constant in
                  consecutive advertisements except when it is
                  explicitly changed in configuration.";
             }
             leaf autonomous-flag {
               type boolean;
               description
                 "The value that is placed in the Autonomous Flag field
                  in the Prefix Information option.";

             }
           }
         }
       }
     }

     /* Configuration data */

     augment "/if:interfaces/if:interface/ip:ipv6" {
       description
         "Augment interface configuration with parameters of IPv6 router
          advertisements.";
       container ipv6-router-advertisements {
         description
           "Configuration of IPv6 Router Advertisements.";
         leaf send-advertisements {
           type boolean;
           default "false";
           description
             "A flag indicating whether or not the router sends periodic
              Router Advertisements and responds to Router
              Solicitations.";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              AdvSendAdvertisements.";
         }
         leaf max-rtr-adv-interval {
           type uint16 {
             range "4..1800";
           }
           units "seconds";
           default "600";
           description
             "The maximum time allowed between sending unsolicited
              multicast Router Advertisements from the interface.";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              MaxRtrAdvInterval.";
         }
         leaf min-rtr-adv-interval {
           type uint16 {
             range "3..1350";
           }
           units "seconds";
           must ". <= 0.75 * ../max-rtr-adv-interval" {
             description
               "The value MUST NOT be greater than 75% of
                'max-rtr-adv-interval'.";

           }
           description
             "The minimum time allowed between sending unsolicited
              multicast Router Advertisements from the interface.

              The default value to be used operationally if this leaf is
              not configured is determined as follows:

              - if max-rtr-adv-interval >= 9 seconds, the default
                value is 0.33 * max-rtr-adv-interval;

              - otherwise, it is 0.75 * max-rtr-adv-interval.";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              MinRtrAdvInterval.";
         }
         leaf managed-flag {
           type boolean;
           default "false";
           description
             "The value to be placed in the 'Managed address
              configuration' flag field in the Router Advertisement.";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              AdvManagedFlag.";
         }
         leaf other-config-flag {
           type boolean;
           default "false";
           description
             "The value to be placed in the 'Other configuration' flag
              field in the Router Advertisement.";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              AdvOtherConfigFlag.";
         }
         leaf link-mtu {
           type uint32;
           default "0";
           description
             "The value to be placed in MTU options sent by the router.
              A value of zero indicates that no MTU options are sent.";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              AdvLinkMTU.";
         }
         leaf reachable-time {
           type uint32 {

             range "0..3600000";
           }
           units "milliseconds";
           default "0";
           description
             "The value to be placed in the Reachable Time field in the
              Router Advertisement messages sent by the router.  A value
              of zero means unspecified (by this router).";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              AdvReachableTime.";
         }
         leaf retrans-timer {
           type uint32;
           units "milliseconds";
           default "0";
           description
             "The value to be placed in the Retrans Timer field in the
              Router Advertisement messages sent by the router.  A value
              of zero means unspecified (by this router).";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              AdvRetransTimer.";
         }
         leaf cur-hop-limit {
           type uint8;
           description
             "The value to be placed in the Cur Hop Limit field in the
              Router Advertisement messages sent by the router.  A value
              of zero means unspecified (by this router).

              If this parameter is not configured, the device SHOULD use
              the value specified in IANA Assigned Numbers that was in
              effect at the time of implementation.";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              AdvCurHopLimit.

              IANA: IP Parameters,
              http://www.iana.org/assignments/ip-parameters";
         }
         leaf default-lifetime {
           type uint16 {
             range "0..9000";
           }
           units "seconds";
           description
             "The value to be placed in the Router Lifetime field of

              Router Advertisements sent from the interface, in seconds.
              It MUST be either zero or between max-rtr-adv-interval and
              9000 seconds.  A value of zero indicates that the router
              is not to be used as a default router.  These limits may
              be overridden by specific documents that describe how IPv6
              operates over different link layers.

              If this parameter is not configured, the device SHOULD use
              a value of 3 * max-rtr-adv-interval.";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              AdvDefaultLifeTime.";
         }
         container prefix-list {
           description
             "Configuration of prefixes to be placed in Prefix
              Information options in Router Advertisement messages sent
              from the interface.

              Prefixes that are advertised by default but do not have
              their entries in the child 'prefix' list are advertised
              with the default values of all parameters.

              The link-local prefix SHOULD NOT be included in the list
              of advertised prefixes.";
           reference
             "RFC 4861: Neighbor Discovery for IP version 6 (IPv6) -
              AdvPrefixList.";
           list prefix {
             key "prefix-spec";
             description
               "Configuration of an advertised prefix entry.";
             leaf prefix-spec {
               type inet:ipv6-prefix;
               description
                 "IPv6 address prefix.";
             }
             choice control-adv-prefixes {
               default "advertise";
               description
                 "Either the prefix is explicitly removed from the
                  set of advertised prefixes, or the parameters with
                  which it is advertised are specified (default case).";
               leaf no-advertise {
                 type empty;
                 description
                   "The prefix will not be advertised.

                    This can be used for removing the prefix from the
                    default set of advertised prefixes.";
               }
               case advertise {
                 leaf valid-lifetime {
                   type uint32;
                   units "seconds";
                   default "2592000";
                   description
                     "The value to be placed in the Valid Lifetime in
                      the Prefix Information option.  The designated
                      value of all 1's (0xffffffff) represents
                      infinity.";
                   reference
                     "RFC 4861: Neighbor Discovery for IP version 6
                      (IPv6) - AdvValidLifetime.";
                 }
                 leaf on-link-flag {
                   type boolean;
                   default "true";
                   description
                     "The value to be placed in the on-link flag
                      ('L-bit') field in the Prefix Information
                      option.";
                   reference
                     "RFC 4861: Neighbor Discovery for IP version 6
                      (IPv6) - AdvOnLinkFlag.";
                 }
                 leaf preferred-lifetime {
                   type uint32;
                   units "seconds";
                   must ". <= ../valid-lifetime" {
                     description
                       "This value MUST NOT be greater than
                        valid-lifetime.";
                   }
                   default "604800";
                   description
                     "The value to be placed in the Preferred Lifetime
                      in the Prefix Information option.  The designated
                      value of all 1's (0xffffffff) represents
                      infinity.";
                   reference
                     "RFC 4861: Neighbor Discovery for IP version 6
                      (IPv6) - AdvPreferredLifetime.";
                 }
                 leaf autonomous-flag {
                   type boolean;

                   default "true";
                   description
                     "The value to be placed in the Autonomous Flag
                      field in the Prefix Information option.";
                   reference
                     "RFC 4861: Neighbor Discovery for IP version 6
                      (IPv6) - AdvAutonomousFlag.";
                 }
               }
             }
           }
         }
       }
     }
   }

   <CODE ENDS>

10. IANA Considerations

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

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

   URI: urn:ietf:params:xml:ns:yang:ietf-ipv4-unicast-routing
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.

   URI: urn:ietf:params:xml:ns:yang:ietf-ipv6-unicast-routing
   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-routing
   Namespace:    urn:ietf:params:xml:ns:yang:ietf-routing
   Prefix:       rt
   Reference:    RFC 8022

   Name:         ietf-ipv4-unicast-routing
   Namespace:    urn:ietf:params:xml:ns:yang:ietf-ipv4-unicast-routing
   Prefix:       v4ur
   Reference:    RFC 8022

   Name:         ietf-ipv6-unicast-routing
   Namespace:    urn:ietf:params:xml:ns:yang:ietf-ipv6-unicast-routing
   Prefix:       v6ur
   Reference:    RFC 8022

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

   Name:         ietf-ipv6-router-advertisements
   Module:       ietf-ipv6-unicast-routing
   Reference:    RFC 8022

11. Security Considerations

   Configuration and state data conforming to the core routing data
   model (defined in this document) are designed to be accessed via a
   management protocol with a secure transport layer, such as NETCONF
   [RFC6241].  The NETCONF access control model [RFC6536] provides the
   means to restrict access for particular NETCONF users to a
   preconfigured subset of all available NETCONF protocol operations and
   content.

   A number of configuration data nodes defined in the YANG modules
   belonging to the core routing data model are writable/creatable/
   deletable (i.e., "config true" in YANG terms, which is the default).
   These data nodes may be considered sensitive or vulnerable in some
   network environments.  Write operations to these data nodes, such as
   "edit-config" in NETCONF, can have negative effects on the network if
   the protocol operations are not properly protected.

   The vulnerable "config true" parameters and subtrees are the
   following:

   /routing/control-plane-protocols/control-plane-protocol:  This list
      specifies the control-plane protocols configured on a device.

   /routing/ribs/rib:  This list specifies the RIBs configured for the
      device.

   Unauthorized access to any of these lists can adversely affect the
   routing subsystem of both the local device and the network.  This may
   lead to network malfunctions, delivery of packets to inappropriate
   destinations, and other problems.

12. References

12.1. 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,
              <http://www.rfc-editor.org/info/rfc2119>.

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

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <http://www.rfc-editor.org/info/rfc4861>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <http://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,
              <http://www.rfc-editor.org/info/rfc6241>.

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

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
              <http://www.rfc-editor.org/info/rfc7223>.

   [RFC7277]  Bjorklund, M., "A YANG Data Model for IP Management",
              RFC 7277, DOI 10.17487/RFC7277, June 2014,
              <http://www.rfc-editor.org/info/rfc7277>.

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

12.2. Informative References

   [RFC6087]  Bierman, A., "Guidelines for Authors and Reviewers of YANG
              Data Model Documents", RFC 6087, DOI 10.17487/RFC6087,
              January 2011, <http://www.rfc-editor.org/info/rfc6087>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <http://www.rfc-editor.org/info/rfc6536>.

   [RFC7895]  Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
              Library", RFC 7895, DOI 10.17487/RFC7895, June 2016,
              <http://www.rfc-editor.org/info/rfc7895>.

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

Appendix A. The Complete Data Trees

   This appendix presents the complete configuration and state data
   trees of the core routing data model.  See Section 2.2 for an
   explanation of the symbols used.  The data type of every leaf node is
   shown near the right end of the corresponding line.

A.1. Configuration Data

      |                             +--rw v4ur:index              string
      |                             +--rw v4ur:outgoing-interface?
      |                             +--rw v4ur:next-hop-address?
      +--rw ribs
         +--rw rib* [name]
            +--rw name              string
            +--rw address-family?   identityref
            +--rw description?      string

A.2. State Data

      +--ro routing-state
      |  +--ro router-id?                 yang:dotted-quad
      |  +--ro interfaces
      |  |  +--ro interface*   if:interface-state-ref
      |  +--ro control-plane-protocols
      |  |  +--ro control-plane-protocol* [type name]
      |  |     +--ro type    identityref
      |  |     +--ro name    string
      |  +--ro ribs
      |     +--ro rib* [name]
      |        +--ro name              string
      |        +--ro address-family    identityref
      |        +--ro default-rib?      boolean {multiple-ribs}?
      |        +--ro routes
      |        |  +--ro route*
      |        |     +--ro route-preference?          route-preference
      |        |     +--ro next-hop
      |        |     |  +--ro (next-hop-options)
      |        |     |     +--:(simple-next-hop)
      |        |     |     |  +--ro outgoing-interface?
      |        |     |     |  +--ro v6ur:next-hop-address?
      |        |     |     |  +--ro v4ur:next-hop-address?
      |        |     |     +--:(special-next-hop)
      |        |     |     |  +--ro special-next-hop?        enumeration
      |        |     |     +--:(next-hop-list)
      |        |     |        +--ro next-hop-list
      |        |     |           +--ro next-hop*
      |        |     |              +--ro outgoing-interface?
      |        |     |              +--ro v6ur:address?
      |        |     |              +--ro v4ur:address?
      |        |     +--ro source-protocol            identityref
      |        |     +--ro active?                    empty
      |        |     +--ro last-updated?              yang:date-and-time
      |        |     +--ro v6ur:destination-prefix?   inet:ipv6-prefix
      |        |     +--ro v4ur:destination-prefix?   inet:ipv4-prefix
      |        +---x active-route
      |           +---w input

Appendix B. Minimum Implementation

   Some parts and options of the core routing model, such as user-
   defined RIBs, are intended only for advanced routers.  This appendix
   gives basic non-normative guidelines for implementing a bare minimum
   of available functions.  Such an implementation may be used for hosts
   or very simple routers.

   A minimum implementation does not support the feature
   "multiple-ribs".  This means that a single system-controlled RIB is
   available for each supported address family -- IPv4, IPv6, or both.
   These RIBs are also the default RIBs.  No user-controlled RIBs are
   allowed.

   In addition to the mandatory instance of the "direct" pseudo-
   protocol, a minimum implementation should support configuring
   instance(s) of the "static" pseudo-protocol.

   For hosts that are never intended to act as routers, the ability to
   turn on sending IPv6 router advertisements (Section 5.4) should be
   removed.

   Platforms with severely constrained resources may use deviations for
   restricting the data model, e.g., limiting the number of "static"
   control-plane protocol instances.

Appendix C. Example: Adding a New Control-Plane Protocol

   This appendix demonstrates how the core routing data model can be
   extended to support a new control-plane protocol.  The YANG module
   "example-rip" shown below is intended as an illustration rather than
   a real definition of a data model for the Routing Information
   Protocol (RIP).  For the sake of brevity, this module does not obey
   all the guidelines specified in [RFC6087].  See also Section 5.3.2.

   module example-rip {

     yang-version "1.1";

     namespace "http://example.com/rip";

     prefix "rip";

     import ietf-interfaces {
       prefix "if";
     }

     import ietf-routing {
       prefix "rt";
     }

     identity rip {
       base rt:routing-protocol;
       description
         "Identity for the Routing Information Protocol (RIP).";
     }

     typedef rip-metric {
       type uint8 {
         range "0..16";
       }
     }

     grouping route-content {
       description
         "This grouping defines RIP-specific route attributes.";
       leaf metric {
         type rip-metric;
       }
       leaf tag {

         type uint16;
         default "0";
         description
           "This leaf may be used to carry additional info, e.g.,
            autonomous system (AS) number.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route" {
       when "derived-from-or-self(rt:source-protocol, 'rip:rip')" {
         description
           "This augment is only valid for a route whose source
            protocol is RIP.";
       }
       description
         "RIP-specific route attributes.";
       uses route-content;
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:active-route/"
           + "rt:output/rt:route" {
       description
         "RIP-specific route attributes in the output of 'active-route'
          RPC.";
       uses route-content;
     }

     augment "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol" {
       when "derived-from-or-self(rt:type,'rip:rip')" {
         description
           "This augment is only valid for a routing protocol instance
            of type 'rip'.";
       }
       container rip {
         presence "RIP configuration";
         description
           "RIP instance configuration.";
         container interfaces {
           description
             "Per-interface RIP configuration.";
           list interface {
             key "name";
             description
               "RIP is enabled on interfaces that have an entry in this
                list, unless 'enabled' is set to 'false' for that
                entry.";
             leaf name {

               type if:interface-ref;
             }
             leaf enabled {
               type boolean;
               default "true";
             }
             leaf metric {
               type rip-metric;
               default "1";
             }
           }
         }
         leaf update-interval {
           type uint8 {
             range "10..60";
           }
           units "seconds";
           default "30";
           description
             "Time interval between periodic updates.";
         }
       }
     }
   }

Appendix D. Data Tree Example

   This section contains an example of an instance data tree in the JSON
   encoding [RFC7951], containing both configuration and state data.
   The data conforms to a data model that is defined by the following
   YANG library specification [RFC7895]:

   {
     "ietf-yang-library:modules-state": {
       "module-set-id": "c2e1f54169aa7f36e1a6e8d0865d441d3600f9c4",
       "module": [
         {
           "name": "ietf-routing",
           "revision": "2016-11-04",
           "feature": [
             "multiple-ribs",
             "router-id"
           ],
           "namespace": "urn:ietf:params:xml:ns:yang:ietf-routing",
           "conformance-type": "implement"
         },
         {
           "name": "ietf-ipv4-unicast-routing",

           "revision": "2016-11-04",
           "namespace":
             "urn:ietf:params:xml:ns:yang:ietf-ipv4-unicast-routing",
           "conformance-type": "implement"
         },
         {
           "name": "ietf-ipv6-unicast-routing",
           "revision": "2016-11-04",
           "namespace":
             "urn:ietf:params:xml:ns:yang:ietf-ipv6-unicast-routing",
           "conformance-type": "implement"
         },
         {
           "name": "ietf-interfaces",
           "revision": "2014-05-08",
           "namespace": "urn:ietf:params:xml:ns:yang:ietf-interfaces",
           "conformance-type": "implement"
         },
         {
           "name": "ietf-inet-types",
           "namespace": "urn:ietf:params:xml:ns:yang:ietf-inet-types",
           "revision": "2013-07-15",
           "conformance-type": "import"
         },
         {
           "name": "ietf-yang-types",
           "namespace": "urn:ietf:params:xml:ns:yang:ietf-yang-types",
           "revision": "2013-07-15",
           "conformance-type": "import"
         },
         {
           "name": "iana-if-type",
           "namespace": "urn:ietf:params:xml:ns:yang:iana-if-type",
           "revision": "",
           "conformance-type": "implement"
         },
         {
           "name": "ietf-ip",
           "revision": "2014-06-16",
           "namespace": "urn:ietf:params:xml:ns:yang:ietf-ip",
           "conformance-type": "implement"
         }
       ]
     }
   }

   A simple network setup as shown in Figure 3 is assumed: router "A"
   uses static default routes with the "ISP" router as the next hop.
   IPv6 router advertisements are configured only on the "eth1"
   interface and disabled on the upstream "eth0" interface.

                   +-----------------+
                   |                 |
                   |    Router ISP   |
                   |                 |
                   +--------+--------+
                            |2001:db8:0:1::2
                            |192.0.2.2
                            |
                            |
                            |2001:db8:0:1::1
                        eth0|192.0.2.1
                   +--------+--------+
                   |                 |
                   |     Router A    |
                   |                 |
                   +--------+--------+
                        eth1|198.51.100.1
                            |2001:db8:0:2::1
                            |

                Figure 3: Example of Network Configuration

   The instance data tree could then be as follows:

   {
     "ietf-interfaces:interfaces": {
       "interface": [
         {
           "name": "eth0",
           "type": "iana-if-type:ethernetCsmacd",
           "description": "Uplink to ISP.",
           "ietf-ip:ipv4": {
             "address": [
               {
                 "ip": "192.0.2.1",
                 "prefix-length": 24
               }
             ],
             "forwarding": true
           },
           "ietf-ip:ipv6": {
             "address": [
               {

                 "ip": "2001:0db8:0:1::1",
                 "prefix-length": 64
               }
             ],
             "forwarding": true,
             "autoconf": {
               "create-global-addresses": false
             }
           }
         },
         {
           "name": "eth1",
           "type": "iana-if-type:ethernetCsmacd",
           "description": "Interface to the internal network.",
           "ietf-ip:ipv4": {
             "address": [
               {
                 "ip": "198.51.100.1",
                 "prefix-length": 24
               }
             ],
             "forwarding": true
           },
           "ietf-ip:ipv6": {
             "address": [
               {
                 "ip": "2001:0db8:0:2::1",
                 "prefix-length": 64
               }
             ],
             "forwarding": true,
             "autoconf": {
               "create-global-addresses": false
             },
             "ietf-ipv6-unicast-routing:ipv6-router-advertisements": {
               "send-advertisements": true
             }
           }
         }
       ]
     },
     "ietf-interfaces:interfaces-state": {
       "interface": [
         {
           "name": "eth0",
           "type": "iana-if-type:ethernetCsmacd",
           "phys-address": "00:0C:42:E5:B1:E9",
           "oper-status": "up",

           "statistics": {
             "discontinuity-time": "2015-10-24T17:11:27+02:00"
           },
           "ietf-ip:ipv4": {
             "forwarding": true,
             "mtu": 1500,
             "address": [
               {
                 "ip": "192.0.2.1",
                 "prefix-length": 24
               }
             ]
           },
           "ietf-ip:ipv6": {
             "forwarding": true,
             "mtu": 1500,
             "address": [
               {
                 "ip": "2001:0db8:0:1::1",
                 "prefix-length": 64
               }
             ],
             "ietf-ipv6-unicast-routing:ipv6-router-advertisements": {
               "send-advertisements": false
             }
           }
         },
         {
           "name": "eth1",
           "type": "iana-if-type:ethernetCsmacd",
           "phys-address": "00:0C:42:E5:B1:EA",
           "oper-status": "up",
           "statistics": {
             "discontinuity-time": "2015-10-24T17:11:29+02:00"
           },
           "ietf-ip:ipv4": {
             "forwarding": true,
             "mtu": 1500,
             "address": [
               {
                 "ip": "198.51.100.1",
                 "prefix-length": 24
               }
             ]
           },
           "ietf-ip:ipv6": {
             "forwarding": true,
             "mtu": 1500,

             "address": [
               {
                 "ip": "2001:0db8:0:2::1",
                 "prefix-length": 64
               }
             ],
             "ietf-ipv6-unicast-routing:ipv6-router-advertisements": {
               "send-advertisements": true,
               "prefix-list": {
                 "prefix": [
                   {
                     "prefix-spec": "2001:db8:0:2::/64"
                   }
                 ]
               }
             }
           }
         }
       ]
     },
     "ietf-routing:routing": {
       "router-id": "192.0.2.1",
       "control-plane-protocols": {
         "control-plane-protocol": [
           {
             "type": "ietf-routing:static",
             "name": "st0",
             "description":
               "Static routing is used for the internal network.",
             "static-routes": {
               "ietf-ipv4-unicast-routing:ipv4": {
                 "route": [
                   {
                     "destination-prefix": "0.0.0.0/0",
                     "next-hop": {
                       "next-hop-address": "192.0.2.2"
                     }
                   }
                 ]
               },
               "ietf-ipv6-unicast-routing:ipv6": {
                 "route": [
                   {
                     "destination-prefix": "::/0",
                     "next-hop": {
                       "next-hop-address": "2001:db8:0:1::2"
                     }
                   }

                 ]
               }
             }
           }
         ]
       }
     },
     "ietf-routing:routing-state": {
       "interfaces": {
         "interface": [
           "eth0",
           "eth1"
         ]
       },
       "control-plane-protocols": {
         "control-plane-protocol": [
           {
             "type": "ietf-routing:static",
             "name": "st0"
           }
         ]
       },
       "ribs": {
         "rib": [
           {
             "name": "ipv4-master",
             "address-family":
               "ietf-ipv4-unicast-routing:ipv4-unicast",
             "default-rib": true,
             "routes": {
               "route": [
                 {
                   "ietf-ipv4-unicast-routing:destination-prefix":
                     "192.0.2.1/24",
                   "next-hop": {
                     "outgoing-interface": "eth0"
                   },
                   "route-preference": 0,
                   "source-protocol": "ietf-routing:direct",
                   "last-updated": "2015-10-24T17:11:27+02:00"
                 },
                 {
                   "ietf-ipv4-unicast-routing:destination-prefix":
                     "198.51.100.0/24",
                   "next-hop": {
                     "outgoing-interface": "eth1"
                   },
                   "source-protocol": "ietf-routing:direct",

                   "route-preference": 0,
                   "last-updated": "2015-10-24T17:11:27+02:00"
                 },
                 {
                   "ietf-ipv4-unicast-routing:destination-prefix":
                     "0.0.0.0/0",
                   "source-protocol": "ietf-routing:static",
                   "route-preference": 5,
                   "next-hop": {
                     "ietf-ipv4-unicast-routing:next-hop-address":
                       "192.0.2.2"
                   },
                   "last-updated": "2015-10-24T18:02:45+02:00"
                 }
               ]
             }
           },
           {
             "name": "ipv6-master",
             "address-family":
               "ietf-ipv6-unicast-routing:ipv6-unicast",
             "default-rib": true,
             "routes": {
               "route": [
                 {
                   "ietf-ipv6-unicast-routing:destination-prefix":
                     "2001:db8:0:1::/64",
                   "next-hop": {
                     "outgoing-interface": "eth0"
                   },
                   "source-protocol": "ietf-routing:direct",
                   "route-preference": 0,
                   "last-updated": "2015-10-24T17:11:27+02:00"
                 },
                 {
                   "ietf-ipv6-unicast-routing:destination-prefix":
                     "2001:db8:0:2::/64",
                   "next-hop": {
                     "outgoing-interface": "eth1"
                   },
                   "source-protocol": "ietf-routing:direct",
                   "route-preference": 0,
                   "last-updated": "2015-10-24T17:11:27+02:00"
                 },
                 {
                   "ietf-ipv6-unicast-routing:destination-prefix":
                     "::/0",
                   "next-hop": {

                     "ietf-ipv6-unicast-routing:next-hop-address":
                       "2001:db8:0:1::2"
                   },
                   "source-protocol": "ietf-routing:static",
                   "route-preference": 5,
                   "last-updated": "2015-10-24T18:02:45+02:00"
                 }
               ]
             }
           }
         ]
       }
     }
   }

Acknowledgments

   The authors wish to thank Nitin Bahadur, Martin Bjorklund, Dean
   Bogdanovic, Jeff Haas, Joel Halpern, Wes Hardaker, Sriganesh Kini,
   David Lamparter, Andrew McGregor, Jan Medved, Xiang Li, Stephane
   Litkowski, Thomas Morin, Tom Petch, Yingzhen Qu, Bruno Rijsman,
   Juergen Schoenwaelder, Phil Shafer, Dave Thaler, Yi Yang,
   Derek Man-Kit Yeung, and Jeffrey Zhang for their helpful comments and
   suggestions.

Authors' Addresses

   Ladislav Lhotka
   CZ.NIC

   Email: lhotka@nic.cz

   Acee Lindem
   Cisco Systems

   Email: acee@cisco.com