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Versions: (draft-lhotka-netmod-routing-cfg) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 15 16 17 18 19 20 21 22 23 24 25 RFC 8022

NETMOD Working Group                                           L. Lhotka
Internet-Draft                                                    CZ.NIC
Intended status: Standards Track                        October 26, 2014
Expires: April 29, 2015


                A YANG Data Model for Routing Management
                    draft-ietf-netmod-routing-cfg-16

Abstract

   This document contains a specification of three YANG modules.
   Together they form the core routing data model which 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 routing protocols and other
   functions.  The core routing data model provides common building
   blocks for such extensions - routing instances, routes, routing
   information bases (RIB), routing protocols and route filters.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 29, 2015.

Copyright Notice

   Copyright (c) 2014 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



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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  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  . . .  10
     4.2.  Features of Advanced Routers  . . . . . . . . . . . . . .  10
   5.  Basic Building Blocks . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Routing Instance  . . . . . . . . . . . . . . . . . . . .  11
       5.1.1.  Parameters of IPv6 Routing Instance Interfaces  . . .  12
     5.2.  Route . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.3.  Routing Information Base (RIB)  . . . . . . . . . . . . .  14
       5.3.1.  Multiple RIBs per Address Family  . . . . . . . . . .  15
     5.4.  Routing Protocol  . . . . . . . . . . . . . . . . . . . .  15
       5.4.1.  Routing Pseudo-Protocols  . . . . . . . . . . . . . .  16
       5.4.2.  Defining New Routing Protocols  . . . . . . . . . . .  18
     5.5.  Route Filter  . . . . . . . . . . . . . . . . . . . . . .  19
     5.6.  RPC Operations  . . . . . . . . . . . . . . . . . . . . .  20
   6.  Interactions with Other YANG Modules  . . . . . . . . . . . .  20
     6.1.  Module "ietf-interfaces"  . . . . . . . . . . . . . . . .  20
     6.2.  Module "ietf-ip"  . . . . . . . . . . . . . . . . . . . .  20
   7.  Routing Management YANG Module  . . . . . . . . . . . . . . .  21
   8.  IPv4 Unicast Routing Management YANG Module . . . . . . . . .  44
   9.  IPv6 Unicast Routing Management YANG Module . . . . . . . . .  49
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  63
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  64
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  65
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  65
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  65
     13.2.  Informative References . . . . . . . . . . . . . . . . .  66
   Appendix A.  The Complete Data Trees  . . . . . . . . . . . . . .  66
     A.1.  Configuration Data  . . . . . . . . . . . . . . . . . . .  66
     A.2.  State Data  . . . . . . . . . . . . . . . . . . . . . . .  69
   Appendix B.  Minimum Implementation . . . . . . . . . . . . . . .  71
   Appendix C.  Example: Adding a New Routing Protocol . . . . . . .  72
   Appendix D.  Example: NETCONF <get> Reply . . . . . . . . . . . .  74
   Appendix E.  Change Log . . . . . . . . . . . . . . . . . . . . .  81
     E.1.  Changes Between Versions -15 and -16  . . . . . . . . . .  81
     E.2.  Changes Between Versions -14 and -15  . . . . . . . . . .  82
     E.3.  Changes Between Versions -13 and -14  . . . . . . . . . .  82



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     E.4.  Changes Between Versions -12 and -13  . . . . . . . . . .  82
     E.5.  Changes Between Versions -11 and -12  . . . . . . . . . .  83
     E.6.  Changes Between Versions -10 and -11  . . . . . . . . . .  83
     E.7.  Changes Between Versions -09 and -10  . . . . . . . . . .  84
     E.8.  Changes Between Versions -08 and -09  . . . . . . . . . .  84
     E.9.  Changes Between Versions -07 and -08  . . . . . . . . . .  84
     E.10. Changes Between Versions -06 and -07  . . . . . . . . . .  84
     E.11. Changes Between Versions -05 and -06  . . . . . . . . . .  85
     E.12. Changes Between Versions -04 and -05  . . . . . . . . . .  85
     E.13. Changes Between Versions -03 and -04  . . . . . . . . . .  86
     E.14. Changes Between Versions -02 and -03  . . . . . . . . . .  86
     E.15. Changes Between Versions -01 and -02  . . . . . . . . . .  87
     E.16. Changes Between Versions -00 and -01  . . . . . . . . . .  87
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  88

1.  Introduction

   This document contains a specification of the following YANG modules:

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

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

   o  Module "ietf-ipv6-unicast-routing" augments the "ietf-routing"
      module with additional data specific to IPv6 unicast, including
      the 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
   routing 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 other 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]:




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   o  client

   o  message

   o  protocol operation

   o  server

   The following terms are defined in [RFC6020]:

   o  augment

   o  configuration data

   o  data model

   o  data node

   o  feature

   o  mandatory node

   o  module

   o  state data

   o  RPC operation

2.1.  Glossary of New Terms

   active route:  a route that is actually used for sending packets.  If
      there are multiple candidate routes with a matching destination
      prefix, then it is up to the routing algorithm to select the
      active route.

   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 5.3 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.



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   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.

   The meaning of the symbols in these diagrams is as follows:

   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), and "ro" state data (read-only).

   o  Symbols after data node names: "?" means an optional node 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

   In this document, names of data nodes, RPC methods and other data
   model objects are often used without a prefix, as long as it is clear
   from the context in which YANG module each name is defined.
   Otherwise, names are prefixed using the standard prefix associated
   with the corresponding YANG module, as shown in Table 1.















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            +--------+---------------------------+-----------+
            | Prefix | YANG module               | Reference |
            +--------+---------------------------+-----------+
            | if     | ietf-interfaces           | [RFC7223] |
            | ip     | ietf-ip                   | [RFC7277] |
            | rt     | ietf-routing              | Section 7 |
            | v4ur   | ietf-ipv4-unicast-routing | Section 8 |
            | v6ur   | ietf-ipv6-unicast-routing | Section 9 |
            | yang   | ietf-yang-types           | [RFC6991] |
            | inet   | ietf-inet-types           | [RFC6991] |
            +--------+---------------------------+-----------+

             Table 1: Prefixes and corresponding YANG modules

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  Simple routing set-ups, such as 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 set-ups involving multiple routing information bases
      (RIB) and multiple routing protocols, as well as controlled
      redistributions of routing information.

   o  Device vendors will want to map the data models built on this
      generic framework to their proprietary data models and
      configuration interfaces.  Therefore, the framework should be
      flexible enough to facilitate such a mapping 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.  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.  Figures 1 and 2 show abridged views of the
   configuration and state data hierarchies.  See Appendix A for the
   complete data trees.



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   +--rw routing
      +--rw routing-instance* [name]
      |  +--rw name
      |  +--rw type?
      |  +--rw enabled?
      |  +--rw router-id?
      |  +--rw description?
      |  +--rw default-ribs
      |  |  +--rw default-rib* [address-family]
      |  |     +--rw address-family
      |  |     +--rw rib-name
      |  +--rw interfaces
      |  |  +--rw interface* [name]
      |  |     +--rw name
      |  |     +--rw v6ur:ipv6-router-advertisements
      |  |           ...
      |  +--rw routing-protocols
      |     +--rw routing-protocol* [type name]
      |        +--rw type
      |        +--rw name
      |        +--rw description?
      |        +--rw enabled?
      |        +--rw route-preference?
      |        +--rw connected-ribs
      |        |     ...
      |        +--rw static-routes
      |              ...
      +--rw ribs
      |  +--rw rib* [name]
      |     +--rw name
      |     +--rw address-family
      |     +--rw description?
      |     +--rw recipient-ribs
      |        +--rw recipient-rib* [rib-name]
      |              ...
      +--rw route-filters
         +--rw route-filter* [name]
            +--rw name
            +--rw description?
            +--rw type

                  Figure 1: Configuration data hierarchy.









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   +--ro routing-state
      +--ro routing-instance* [name]
      |  +--ro name
      |  +--ro id
      |  +--ro type?
      |  +--ro default-ribs
      |  |  +--ro default-rib* [address-family]
      |  |     +--ro address-family
      |  |     +--ro rib-name
      |  +--ro interfaces
      |  |  +--ro interface* [name]
      |  |     +--ro name
      |  |     +--ro v6ur:ipv6-router-advertisements
      |  |           ...
      |  +--ro routing-protocols
      |     +--ro routing-protocol* [type name]
      |        +--ro type
      |        +--ro name
      |        +--ro route-preference
      |        +--ro connected-ribs
      |              ...
      +--ro next-hop-lists
      |  +--ro next-hop-list* [id]
      |     +--ro id
      |     +--ro address-family
      |     +--ro next-hop*
      |        +--ro (next-hop-options)
      |        |     ...
      |        +--ro priority?
      |        +--ro weight?
      +--ro ribs
      |  +--ro rib* [name]
      |     +--ro name
      |     +--ro id
      |     +--ro address-family
      |     +--ro routes
      |     |  +--ro route*
      |     |        ...
      |     +--ro recipient-ribs
      |        +--ro recipient-rib* [rib-name]
      |              ...
      +--ro route-filters
         +--ro route-filter* [name]
            +--ro name
            +--ro type

                      Figure 2: State data hierarchy.




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   As can be seen from Figures 1 and 2, the core routing data model
   introduces several generic components of a routing framework: routing
   instances, RIBs containing lists of routes, routing protocols and
   route filters.  The following subsections describe these components
   in more detail.

   By combining the components in various ways, and possibly augmenting
   them with appropriate contents defined in other modules, various
   routing systems can be realized.

   +--------+
   | direct |    +---+    +--------------+    +---+    +--------------+
   | routes |--->| F |--->|              |<---| F |<---|              |
   +--------+    +---+    |   default    |    +---+    |  additional  |
                          |     RIB      |             |     RIB      |
   +--------+    +---+    |              |    +---+    |              |
   | static |--->| F |--->|              |--->| F |--->|              |
   | routes |    +---+    +--------------+    +---+    +--------------+
   +--------+                 ^      |                     ^      |
                              |      v                     |      v
                            +---+  +---+                 +---+  +---+
                            | F |  | F |                 | F |  | F |
                            +---+  +---+                 +---+  +---+
                              ^      |                     ^      |
                              |      v                     |      v
                            +----------+                 +----------+
                            | routing  |                 | routing  |
                            | protocol |                 | protocol |
                            +----------+                 +----------+

               Figure 3: Example set-up of a routing system

   The example in Figure 3 shows a typical (though certainly not the
   only possible) organization of a more complex routing subsystem for a
   single address family.  Several of its features are worth mentioning:

   o  Along with the default RIB, which is always present, an additional
      RIB is configured.

   o  Each routing protocol instance, including the "static" and
      "direct" pseudo-protocols, is connected to exactly one RIB with
      which it can exchange routes (in both directions, except for the
      "static" and "direct" pseudo-protocols).

   o  RIBs may also be connected to each other and exchange routes in
      either direction (or both).





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   o  Route exchanges along all connections may be controlled by means
      of route filters, denoted by "F" in Figure 3.

4.1.  System-Controlled and User-Controlled List Entries

   The core routing data model defines several lists, for example
   "routing-instance" or "rib", that have to be populated with at least
   one entry in any properly functioning device, and additional entries
   may be configured by the user.

   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.

   Additional entries may be created in the configuration by the user,
   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.

   The user may also provide supplemental configuration of system-
   controlled entries.  To do so, the user creates a new entry in the
   configuration with the desired contents.  In order to bind this entry
   with 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.

   An example can be seen in Appendix D: the "/routing-state/routing-
   instance" list has a single system-controlled entry whose "name" key
   has the value "rtr0".  This entry is configured by the "/routing/
   routing-instance" entry whose "name" key is also "rtr0".

   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.

4.2.  Features of Advanced Routers

   The core routing data model attempts to address devices with
   elementary routing functions as well as advanced routers.  For simple
   devices, some parts and options of the data model are not needed and
   would represent unnecessary complications for the implementation.
   Therefore, the core routing data model makes the configuration of



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   some advanced functions optional to implement by means of two YANG
   features:

   o  "multiple-ribs" - indicates that the device supports configuration
      of user-defined RIBs, routing protocols connected to non-default
      RIBs, and RIBs configured as receivers of routes from other RIBs.

   o  "multipath-routes" - indicates that the device supports
      configuration of routes with multiple next-hops.

   See the "ietf-routing" module for details.

5.  Basic Building Blocks

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

5.1.  Routing Instance

   The core routing data model supports one or more routing instances
   appearing as entries of the "routing-instance" list.  Each routing
   instance has separate configuration and state data under
   "/rt:routing/rt:routing-instance" and "/rt:routing-state/rt:routing-
   instance", respectively.

   The semantics of the term "routing instance" is deliberately left
   undefined.  It is expected that future YANG modules will define data
   models for specific types of routing instances, such as VRF (virtual
   routing and forwarding) instances that are used for BGP/MPLS virtual
   private networks [RFC4364].  For each type of routing instance, an
   identity derived from "rt:routing-instance" MUST be defined.  This
   identity is then referred to by the value of the "type" leaf (a child
   node of "routing-instance" list).

   An implementation MAY create one or more system-controlled routing
   instances, and MAY also impose restrictions on types of routing
   instances that can be configured, and on the maximum number of
   supported instances for each type.  For example, a simple router
   implementation may support only one system-controlled routing
   instance of the default type "rt:default-routing-instance" and may
   not allow creation of any user-controlled instances.

   Each network layer interface has to be assigned to one or more
   routing instances in order to be able to participate in packet
   forwarding, routing protocols and other operations of those routing
   instances.  The assignment is accomplished by placing a corresponding
   (system- or user-controlled) entry in the list of routing instance
   interfaces ("rt:interface").  The key of the list entry is the name



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   of a configured network layer interface, see the "ietf-interfaces"
   module [RFC7223].

   A data model for a routing instance type MAY state additional rules
   for the assignment of interfaces to routing instances of that type.
   For example, it may be required that the sets of interfaces assigned
   to different routing instances of a certain type be disjoint.

5.1.1.  Parameters of IPv6 Routing Instance Interfaces

   The module "ietf-ipv6-unicast-routing" augments the definition of the
   data node "rt:interface", in both configuration and state data, with
   definitions of the following variables as required by [RFC4861], sec.
   6.2.1:

   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.




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   The definitions and descriptions of the above parameters can be found
   in the module "ietf-ipv6-unicast-routing" (Section 9).

   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-unicast-routing" module therefore
       assumes the former behavior with constant values.

5.2.  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": IP 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 action to be performed with a packet.
      See below for details.

   The choice of next-hops comprises the following cases:

   o  simple next-hop - IP address of the next-hop router, outgoing
      interface, or both.

   o  special next-hop - a keyword indicating special packet handling,
      one of:

      *  "blackhole" - silently discard the packet;





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      *  "unreachable" - discard the packet and notify the sender with a
         "destination unreachable" error message;

      *  "prohibit" - discard the packet notify the sender with an
         "administratively prohibited" error message.

   o  next-hop list reference - each next-hop list is a set of next-hops
      that may also contain a reference to another next-hop list.

   o  RIB reference - a new look-up is to be performed in the specified
      RIB.

   It is expected that future modules defining routing protocols will
   add other route attributes such as metrics or preferences.

   Routes are primarily state data that appear as entries of RIBs
   (Section 5.3) but they may be also found in configuration data, for
   example as manually configured static routes.  In the latter case,
   configurable route attributes are generally a subset of route
   attributes described above.

5.3.  Routing Information Base (RIB)

   A routing information base (RIB) is a list of routes complemented
   with administrative data, namely:

   o  "source-protocol": type of the routing protocol from which the
      route was originally obtained.

   o  "preferred": an implementation can use this empty leaf to indicate
      that the route is preferred among all routes in the same RIB that
      have the same destination prefix.

   o  "last-updated": the date and time when the route was last updated,
      or inserted into the RIB.

   Each RIB MUST contain only routes of one address family.  In the data
   model, address family is represented with 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 routing protocol operations which
   may result in route additions, removals and modifications.  This also
   includes manipulations via the "static" and/or "direct" pseudo-
   protocols, see Section 5.4.1.





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   RIBs are global, which means that a RIB may be used by any or all
   routing instances.  However, a data model for a routing instance type
   MAY state rules and restrictions for sharing RIBs among routing
   instances of that type.

   Each routing instance has, for every supported address family, one
   RIB selected as the so-called default RIB.  This selection is
   recorded in the list "default-rib".  The role of default RIBs is
   explained in Section 5.4.

   Simple router implementations that do not advertise the feature
   "multiple-ribs" will typically create one system-controlled RIB per
   supported address family, and declare it as the default RIB (via a
   system-controlled entry of the "default-rib" list).

5.3.1.  Multiple RIBs per Address Family

   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.  Every RIB can then serve as a
   source of routes for other RIBs of the same address family.  To
   achieve this, one or more recipient RIBs may be specified in the
   configuration of the source RIB.  Optionally, a route filter may be
   configured for any or all recipient RIBs.  Such a route filter then
   selects and/or manipulates the routes that are passed between the
   source and recipient RIB.

   A RIB MUST NOT appear among its own recipient RIBs.

5.4.  Routing Protocol

   The core routing data model provides an open-ended framework for
   defining multiple routing protocol instances within a routing
   instance.  Each routing protocol instance MUST be assigned a type,
   which is an identity derived from the "rt:routing-protocol" base
   identity.  The core routing data model defines two identities for the
   direct and static pseudo-protocols (Section 5.4.1).

   Multiple routing protocol instances of the same type are permitted.

   Each routing protocol instance can be connected to one or more RIBs
   for each address family that the routing protocol instance supports.
   By default, the interaction of a routing protocol instance with its
   connected RIBs is governed by the following rules:

   o  Routes learned from the network are installed in all connected
      RIBs with a matching address family.




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   o  Conversely, routes from all connected RIBs are injected into the
      routing protocol instance.

   However, a data model for a routing protocol MAY impose specific
   rules for exchanging routes between routing protocol instances and
   connected RIBs.

   On devices supporting the "multiple-ribs" feature, any RIB (system-
   controlled or user-controlled) may be connected to a routing protocol
   instance by configuring a corresponding entry in the "connected-rib"
   list.  If such an entry is not configured for an address family, then
   the default RIB MUST be used as the connected RIB for this address
   family.

   In addition, two independent route filters (see Section 5.5) may be
   configured for each connected RIB to apply user-defined policies
   controlling the exchange of routes in both directions between the
   routing protocol instance and the connected RIB:

   o  import filter controls which routes are passed from the routing
      protocol instance to the connected RIB,

   o  export filter controls which routes the routing protocol instance
      receives from the connected RIB.

   Note that the terms import and export are used from the viewpoint of
   a RIB.

5.4.1.  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 they are confined to the local device and do not exchange
   any routing information with adjacent routers.  Routes from both
   "direct" and "static" protocol instances are passed to the connected
   RIBs (subject to route filters, if any), but an exchange in the
   opposite direction is not allowed.

   Every routing instance MUST implement 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.  The "direct" pseudo-protocol
   MUST always be connected to the default RIBs of all supported address
   families.  Unlike other routing protocol types, this connection
   cannot be changed in the configuration.  Direct routes MAY be
   filtered before they appear in the default RIB.




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   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 per
   routing instance.

   Static routes are configured within the "static-routes" container,
   see Figure 4.

   +--rw static-routes
      +--rw v4ur:ipv4
      |  +--rw v4ur:route* [destination-prefix]
      |     +--rw v4ur:destination-prefix
      |     +--rw v4ur:description?
      |     +--rw v4ur:next-hop
      |        +--rw (simple-or-list)?
      |           +--:(multipath-entry)
      |           |  +--rw v4ur:multipath-entry* [name]
      |           |     +--rw v4ur:name
      |           |     +--rw (next-hop-options)
      |           |     |  +--:(simple-next-hop)
      |           |     |  |  +--rw v4ur:outgoing-interface?
      |           |     |  +--:(special-next-hop)
      |           |     |  |  +--rw v4ur:special-next-hop?
      |           |     |  +--:(next-hop-address)
      |           |     |     +--rw v4ur:next-hop-address?
      |           |     +--rw v4ur:priority?
      |           |     +--rw v4ur:weight?
      |           +--:(simple-next-hop)
      |              +--rw (next-hop-options)
      |                 +--:(simple-next-hop)
      |                 |  +--rw v4ur:outgoing-interface?
      |                 +--:(special-next-hop)
      |                 |  +--rw v4ur:special-next-hop?
      |                 +--:(next-hop-address)
      |                    +--rw v4ur:next-hop-address?
      +--rw v6ur:ipv6
         +--rw v6ur:route* [destination-prefix]
            +--rw v6ur:destination-prefix
            +--rw v6ur:description?
            +--rw v6ur:next-hop
               +--rw (simple-or-list)?
                  +--:(multipath-entry)
                  |  +--rw v6ur:multipath-entry* [name]
                  |     +--rw v6ur:name
                  |     +--rw (next-hop-options)
                  |     |  +--:(simple-next-hop)
                  |     |  |  +--rw v6ur:outgoing-interface?
                  |     |  +--:(special-next-hop)



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                  |     |  |  +--rw v6ur:special-next-hop?
                  |     |  +--:(next-hop-address)
                  |     |     +--rw v6ur:next-hop-address?
                  |     +--rw v6ur:priority?
                  |     +--rw v6ur:weight?
                  +--:(simple-next-hop)
                     +--rw (next-hop-options)
                        +--:(simple-next-hop)
                        |  +--rw v6ur:outgoing-interface?
                        +--:(special-next-hop)
                        |  +--rw v6ur:special-next-hop?
                        +--:(next-hop-address)
                           +--rw v6ur:next-hop-address?

              Figure 4: Structure of "static-routes" subtree.

   A next-hop in static routes may be configured as a simple next-hop
   (IP address, outgoing interface or both), special next-hop or a list
   of multi-path next-hop entries that is used either for backup routes
   of for equal-cost multi-path (ECMP) routing.  The last option is
   available only on devices that advertise the feature "rt:multipath-
   routes".  Moreover, unlike next-hop lists in state data, a list of
   next-hop entries in a static route cannot be recursive, i.e., each
   entry of that list can only be a simple or special next-hop.

5.4.2.  Defining New Routing Protocols

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

   o  A new identity MUST be defined for the routing protocol and its
      base identity MUST be set to "rt:routing-protocol", or to an
      identity derived from "rt:routing-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:fib-route/rt:output/rt:route,

      and possibly other places in the configuration, state data and RPC
      input or output.



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

   o  Per-interface configuration, including activation of the routing
      protocol on individual interfaces, can use references to entries
      in the list of routing instance interfaces (rt:interface).

   By using the "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 the new protocol's identity.  It is also
   RECOMMENDED that protocol-specific data nodes be encapsulated in
   appropriately named containers.

   The above steps are implemented by the example YANG module for the
   RIP routing protocol in Appendix C.

5.5.  Route Filter

   The core routing data model provides a skeleton for defining route
   filters that can be used to restrict the set of routes being
   exchanged between a routing protocol instance and a connected RIB, or
   between a source and a recipient RIB.  Route filters may also
   manipulate routes, i.e., add, delete, or modify their attributes.

   Route filters are global, which means that a configured route filter
   may be used by any or all routing instances.  However, a data model
   for a routing instance type MAY specify rules and restrictions for
   sharing route filters among routing instances of that type.

   The core routing data model defines only two extreme route filtering
   policies which are represented by the following pre-defined route
   filter types:

   o  "deny-all-route-filter": all routes are blocked,

   o  "allow-all-route-filter": all routes are permitted.

   The latter type is equivalent to no route filter.

   It is expected that more comprehensive route filtering frameworks
   will be developed separately.

   Each route filter entry is identified by a unique name.  Its type
   MUST be specified by the "type" identity reference.





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5.6.  RPC Operations

   The "ietf-routing" module defines two RPC operations:

   o  fib-route: query a routing instance for the active route in the
      Forwarding Information Base (FIB).  It is the route that is
      currently used for sending datagrams to a destination host whose
      address is passed as an input parameter.

   o  route-count: retrieve the total number of entries in a RIB.

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,
      the device MUST behave exactly as if that interface was not
      assigned to any routing instance at all.

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 functions related to that interface MUST be
      disabled.

   /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 to and from 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





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      If this switch is set to "false" for a network layer interface,
      then all IPv6 routing functions related to that interface MUST be
      disabled.

   /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 to and from 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

   RFC Editor: In this section, replace all occurrences of 'XXXX' with
   the actual RFC number and all occurrences of the revision date below
   with the date of RFC publication (and remove this note).

   <CODE BEGINS> file "routing@2014-10-26.yang"

   module ietf-routing {

     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:   <http://tools.ietf.org/wg/netmod/>
        WG List:  <mailto:netmod@ietf.org>




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        WG Chair: Thomas Nadeau
                  <mailto:tnadeau@lucidvision.com>

        WG Chair: Juergen Schoenwaelder
                  <mailto:j.schoenwaelder@jacobs-university.de>

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

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

        Copyright (c) 2014 IETF Trust and the persons identified as
        authors of the code. All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Simplified BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

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

     revision 2014-10-26 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: A YANG Data Model for Routing Management";
     }

     /* Features */

     feature multiple-ribs {
       description
         "This feature indicates that the server supports user-defined
          RIBS and the framework for passing routes between RIBs.

          Servers that do not advertize this feature MUST provide
          exactly one system-controlled RIB per supported address family
          and make them also the default RIBs. These RIBs then appear as
          entries of the list /routing-state/ribs/rib.";
     }

     feature multipath-routes {
       description



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         "This feature indicates that the server supports multipath
          routes that have a list of next-hops.";
     }

     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 advertize this feature set a router ID
          algorithmically, usually to one of 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 routing-instance {
       description
         "Base identity from which identities describing routing
          instance types are derived.";
     }

     identity default-routing-instance {
       base routing-instance;
       description
         "This identity represents either a default routing instance, or
          the only routing instance on systems that do not support
          multiple instances.";
     }



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

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

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

     identity route-filter {
       description
         "Base identity from which all route filters are derived.";
     }

     identity deny-all-route-filter {
       base route-filter;
       description
         "Route filter that blocks all routes.";
     }

     identity allow-all-route-filter {
       base route-filter;
       description
         "Route filter that permits all routes.";
     }

     /* Type Definitions */

     typedef routing-instance-ref {
       type leafref {
         path "/rt:routing/rt:routing-instance/rt:name";
       }
       description
         "This type is used for leafs that reference a routing instance
          configuration.";
     }

     typedef routing-instance-state-ref {



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       type leafref {
         path "/rt:routing-state/rt:routing-instance/rt:name";
       }
       description
         "This type is used for leafs that reference state data of a
          routing instance.";
     }

     typedef rib-ref {
       type leafref {
         path "/rt:routing/rt:ribs/rt:rib/rt:name";
       }
       description
         "This type is used for leafs that reference a RIB
          configuration.";
     }

     typedef rib-state-ref {
       type leafref {
         path "/rt:routing-state/rt:ribs/rt:rib/rt:name";
       }
       description
         "This type is used for leafs that reference a RIB in state
          data.";
     }

     typedef next-hop-list-ref {
       type leafref {
         path "/rt:routing-state/rt:next-hop-lists/rt:next-hop-list/"
            + "rt:id";
       }
       description
         "This type is used for leafs that reference a next-hop list (in
          state data).";
     }

     typedef route-filter-ref {
       type leafref {
         path "/rt:routing/rt:route-filters/rt:route-filter/rt:name";
       }
       description
         "This type is used for leafs that reference a route filter
          configuration.";
     }

     typedef route-filter-state-ref {
       type leafref {
         path "/rt:routing-state/rt:route-filters/rt:route-filter/"



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            + "rt:name";
       }
       description
         "This type is used for leafs that reference state data of a
          route filter.";
     }

     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 state-entry-id {
       description
         "This grouping provides a unique identifier for entries in
          several operational state lists.";
       leaf id {
         type uint64;
         description
           "Unique numerical identifier of a list entry in operational
            state. It may be used by protocols or tools that inspect
            and/or manipulate operational state data and prefer
            fixed-size integers as list entry handles.

            These identifiers are always ephemeral, i.e., they may
            change after a reboot.";
       }
     }

     grouping router-id {
       description



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         "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 next-hop-classifiers {
       description
         "This grouping provides two next-hop classifiers.";
       leaf priority {
         type enumeration {
           enum primary {
             value "1";
             description
               "Primary next-hop.";
           }
           enum backup {
             value "2";
             description
               "Backup next-hop.";
           }
         }
         description
           "Simple priority for distinguishing between primary and
            backup next-hops.

            Backup next-hops are used if and only if no primary
            next-hops are reachable.";
       }
       leaf weight {
         type uint8;
         must ". = 0 or not(../../next-hop/weight = 0)" {
           error-message "Illegal combination of zero and non-zero "
                       + "next-hop weights.";
           description
             "Next-hop weights must be either all zero (equal
              load-balancing) or all non-zero.";
         }
         description
           "This parameter specifies the weight of the next-hop for load
            balancing. The number specifies the relative fraction of the
            traffic that will use the corresponding next-hop.




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            A value of 0 represents equal load-balancing.

            If both primary and backup next-hops are present, then the
            weights for each priority level are used separately.";
       }
     }

     grouping special-next-hop {
       description
         "This grouping provides a leaf with 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
           "Special next-hop options.";
       }
     }

     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.";
         case simple-next-hop {
           description



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             "Simple next-hop is specified as an outgoing interface,
              next-hop address or both.

              Address-family-specific modules are expected to provide
              'next-hop-address' leaf via augmentation.";
           leaf outgoing-interface {
             type leafref {
               path "/rt:routing/rt:routing-instance/rt:interfaces/"
                  + "rt:interface/rt:name";
             }
             description
               "Name of the outgoing interface.";
           }
         }
         case special-next-hop {
           uses special-next-hop;
         }
       }
     }

     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.";
         leaf next-hop-list {
           type next-hop-list-ref;
           description
             "Reference to a next-hop list.";
         }
         leaf use-rib {
           type rib-state-ref;
           description
             "Reference to a RIB in which a new look-up is to be
              performed.";
         }
         case simple-next-hop {
           description
             "Simple next-hop is specified as an outgoing interface,
              next-hop address or both.

              Address-family-specific modules are expected to provide
              'next-hop-address' leaf via augmentation.";
           leaf outgoing-interface {
             type leafref {
               path "/rt:routing-state/rt:routing-instance/"



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                  + "rt:interfaces/rt:interface/rt:name";
             }
             description
               "Name of the outgoing interface.";
           }
         }
         case special-next-hop {
           uses special-next-hop;
         }
       }
     }

     grouping route-metadata {
       description
         "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.";
       }
     }

     /* Operational state data */

     container routing-state {
       config "false";
       description
         "Operational state of the routing subsystem.";
       list routing-instance {
         key "name";



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         unique "id";
         min-elements "1";
         description
           "Each list entry is a container for operational state data of
            a routing instance.

            An implementation MAY create one or more system-controlled
            instances, other user-controlled instances MAY be created by
            configuration.";
         leaf name {
           type string;
           description
             "The name of the routing instance.

              For system-controlled instances the name is persistent,
              i.e., it SHOULD NOT change across reboots.";
         }
         uses state-entry-id {
           refine "id" {
             mandatory "true";
           }
         }
         leaf type {
           type identityref {
             base routing-instance;
           }
           description
             "The routing instance type.";
         }
         container default-ribs {
           description
             "Default RIBs used by the routing instance.";
           list default-rib {
             key "address-family";
             description
               "Each list entry specifies the default RIB for one
                address family.

                The default RIB is operationally connected to all
                routing protocols for which a connected RIB has not been
                explicitly configured.

                The 'direct' pseudo-protocol is always connected to the
                default RIBs.";
             uses address-family;
             leaf rib-name {
               type rib-state-ref;
               mandatory "true";



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               description
                 "Name of an existing RIB to be used as the default RIB
                  for the given routing instance and address family.";
             }
           }
         }
         container interfaces {
           description
             "Network layer interfaces belonging to the routing
              instance.";
           list interface {
             key "name";
             description
               "List of network layer interfaces assigned to the routing
                instance.";
             leaf name {
               type if:interface-state-ref;
               description
                 "A reference to the name of a configured network layer
                  interface.";
             }
           }
         }
         container routing-protocols {
           description
             "Container for the list of routing protocol instances.";
           list routing-protocol {
             key "type name";
             description
               "Operational state of a routing protocol instance.

                An implementation MUST provide exactly one
                system-controlled instance of the type 'direct'. Other
                instances MAY be created by configuration.";
             leaf type {
               type identityref {
                 base routing-protocol;
               }
               description
                 "Type of the routing protocol.";
             }
             leaf name {
               type string;
               description
                 "The name of the routing protocol instance.

                  For system-controlled instances this name is
                  persistent, i.e., it SHOULD NOT change across



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                  reboots.";
             }
             leaf route-preference {
               type route-preference;
               mandatory "true";
               description
                 "The value of route preference (administrative
                  distance) assigned to all routes generated by the
                  routing protocol instance. A lower value means a more
                  preferred route.";
             }
             container connected-ribs {
               description
                 "Container for connected RIBs.";
               list connected-rib {
                 key "rib-name";
                 description
                   "List of RIBs to which the routing protocol instance
                    is connected.

                    By default, routes learned by the routing protocol
                    instance are installed in all connected RIBs of the
                    matching address family, and, conversely, all routes
                    from connected RIBs are installed in the routing
                    protocol instance. However, routing protocols may
                    specify other rules.";
                 leaf rib-name {
                   type rib-state-ref;
                   description
                     "Name of an existing RIB.";
                 }
                 leaf import-filter {
                   type route-filter-state-ref;
                   description
                     "Reference to a route filter that is used for
                      filtering routes passed from this routing protocol
                      instance to the RIB specified by the 'rib-name'
                      sibling node.

                      If this leaf is not present, the behavior is
                      protocol-specific, but typically it means that all
                      routes are accepted.";
                 }
                 leaf export-filter {
                   type route-filter-state-ref;
                   description
                     "Reference to a route filter that is used for
                      filtering routes passed from the RIB specified by



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                      the 'rib-name' sibling node to this routing
                      protocol instance.

                      If this leaf is not present, the behavior is
                      protocol-specific - typically it means that all
                      routes are accepted.

                      The 'direct' and 'static' pseudo-protocols accept
                      no routes from any RIB.";
                 }
               }
             }
           }
         }
       }
       container next-hop-lists {
         description
           "Container for next-hop lists.";
         list next-hop-list {
           key "id";
           description
             "Next-hop list.";
           uses state-entry-id;
           uses address-family;
           list next-hop {
             description
               "Entry in a next-hop list.";
             uses next-hop-state-content;
             uses next-hop-classifiers;
           }
         }
       }
       container ribs {
         description
           "Container for RIBs.";
         list rib {
           key "name";
           unique "id";
           description
             "Each entry represents a RIB identified by the 'name' key.
              All routes in a RIB MUST belong to the same address
              family.

              The server MUST provide a system-controlled default RIB
              for each address family, and MAY provide other
              system-controlled RIBs. Additional RIBs MAY be created in
              the configuration.";
           leaf name {



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             type string;
             description
               "The name of the RIB.";
           }
           uses state-entry-id {
             refine "id" {
               mandatory "true";
             }
           }
           uses address-family;
           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;
             }
           }
           container recipient-ribs {
             description
               "Container for recipient RIBs.";
             list recipient-rib {
               key "rib-name";
               description
                 "List of RIBs that receive routes from this RIB.";
               leaf rib-name {
                 type rib-state-ref;
                 description
                   "The name of the recipient RIB.";
               }
               leaf filter {
                 type route-filter-state-ref;



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                 description
                   "A route filter which is applied to the routes passed
                    to the recipient RIB.";
               }
             }
           }
         }
       }
       container route-filters {
         description
           "Container for route filters.";
         list route-filter {
           key "name";
           description
             "Route filters are used for filtering and/or manipulating
              routes that are passed between a routing protocol and a
              RIB and vice versa, or between two RIBs.

              It is expected that other modules augment this list with
              contents specific for a particular route filter type.";
           leaf name {
             type string;
             description
               "The name of the route filter.";
           }
           leaf type {
             type identityref {
               base route-filter;
             }
             mandatory "true";
             description
               "Type of the route-filter - an identity derived from the
                'route-filter' base identity.";
           }
         }
       }
     }

     /* Configuration Data */

     container routing {
       description
         "Configuration parameters for the routing subsystem.";
       list routing-instance {
         key "name";
         description
           "Configuration of a routing instance.";
         leaf name {



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           type string;
           description
             "The name of the routing instance.

              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.";
         }
         leaf type {
           type identityref {
             base routing-instance;
           }
           default "rt:default-routing-instance";
           description
             "The type of the routing instance.";
         }
         leaf enabled {
           type boolean;
           default "true";
           description
             "Enable/disable the routing instance.

              If this parameter is false, the parent routing instance is
              disabled and does not appear in operational state data,
              despite any other configuration that might be present.";
         }
         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.";
         }
         leaf description {
           type string;
           description
             "Textual description of the routing instance.";
         }
         container default-ribs {
           if-feature multiple-ribs;
           description
             "Configuration of the default RIBs used by the routing
              instance.

              The default RIB for an addressed family if by default



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              connected to all routing protocol instances supporting
              that address family, and always receives direct routes.";
           list default-rib {
             must "address-family=/routing/ribs/rib[name=current()/"
                + "rib-name]/address-family" {
               error-message "Address family mismatch.";
               description
                 "The entry's address family MUST match that of the
                  referenced RIB.";
             }
             key "address-family";
             description
               "Each list entry configures the default RIB for one
                address family.";
             uses address-family;
             leaf rib-name {
               type string;
               mandatory "true";
               description
                 "Name of an existing RIB to be used as the default RIB
                  for the given routing instance and address family.";
             }
           }
         }
         container interfaces {
           description
             "Configuration of the routing instance's interfaces.";
           list interface {
             key "name";
             description
               "List of network layer interfaces assigned to the routing
                instance.";
             leaf name {
               type if:interface-ref;
               description
                 "A reference to the name of a configured network layer
                  interface.";
             }
           }
         }
         container routing-protocols {
           description
             "Configuration of routing protocol instances.";
           list routing-protocol {
             key "type name";
             description
               "Each entry contains configuration of a routing protocol
                instance.";



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             leaf type {
               type identityref {
                 base routing-protocol;
               }
               description
                 "Type of the routing protocol - an identity derived
                  from the 'routing-protocol' base identity.";
             }
             leaf name {
               type string;
               description
                 "An arbitrary name of the routing protocol instance.";
             }
             leaf description {
               type string;
               description
                 "Textual description of the routing protocol
                  instance.";
             }
             leaf enabled {
               type boolean;
               default "true";
               description
                 "Enable/disable the routing protocol instance.

                  If this parameter is false, the parent routing
                  protocol instance is disabled and does not appear in
                  operational state data, despite any other
                  configuration that might be present.";
             }
             leaf route-preference {
               type route-preference;
               description
                 "The value of route preference (administrative
                  distance).

                  The default value depends on the routing protocol
                  type, and may also be implementation-dependent.";
             }
             container connected-ribs {
               description
                 "Configuration of connected RIBs.";
               list connected-rib {
                 key "rib-name";
                 description
                   "Each entry configures a RIB to which the routing
                    protocol instance is connected.




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                    If no connected RIB is configured for an address
                    family, the routing protocol is connected to the
                    default RIB for that address family.";
                 leaf rib-name {
                   type rib-ref;
                   must "../../../type != 'rt:direct' or "
                      + "../../../../../default-ribs/ "
                      + "default-rib/rib-name=." {
                     error-message "The 'direct' protocol can be "
                                 + "connected only to a default RIB.";
                     description
                       "For the 'direct' pseudo-protocol, the connected
                        RIB must always be a default RIB.";
                   }
                   description
                     "Name of an existing RIB.";
                 }
                 leaf import-filter {
                   type route-filter-ref;
                   description
                     "Configuration of import filter.";
                 }
                 leaf export-filter {
                   type route-filter-ref;
                   description
                     "Configuration of export filter.";
                 }
               }
             }
             container static-routes {
               when "../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 {



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           key "name";
           description
             "Each entry represents a configured 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;
           leaf description {
             type string;
             description
               "Textual description of the RIB.";
           }
           container recipient-ribs {
             if-feature multiple-ribs;
             description
               "Configuration of recipient RIBs.";
             list recipient-rib {
               must "rib-name != ../../name" {
                 error-message
                   "Source and recipient RIBs are identical.";
                 description
                   "A RIB MUST NOT appear among its recipient RIBs.";
               }
               must "/routing/ribs/rib[name=current()/rib-name]/"
                  + "address-family=../../address-family" {
                 error-message "Address family mismatch.";
                 description
                   "Address family of the recipient RIB MUST match that
                    of the source RIB.";
               }
               key "rib-name";
               description
                 "Each entry configures a recipient RIB.";



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               leaf rib-name {
                 type rib-ref;
                 description
                   "The name of the recipient RIB.";
               }
               leaf filter {
                 type route-filter-ref;
                 description
                   "A route filter which is applied to the routes passed
                    to the recipient RIB.";
               }
             }
           }
         }
       }
       container route-filters {
         description
           "Configuration of route filters.";
         list route-filter {
           key "name";
           description
             "Each entry configures a named route filter.";
           leaf name {
             type string;
             description
               "The name of the route filter.";
           }
           leaf description {
             type string;
             description
               "Textual description of the route filter.";
           }
           leaf type {
             type identityref {
               base route-filter;
             }
             mandatory "true";
             description
               "Type of the route filter..";
           }
         }
       }
     }

     /* RPC methods */

     rpc fib-route {
       description



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         "Return the active FIB route that a routing-instance uses for
          sending packets to a destination address.";
       input {
         leaf routing-instance-name {
           type routing-instance-state-ref;
           mandatory "true";
           description
             "Name of the routing instance whose forwarding information
              base is being queried.

              If the routing instance with name equal to the value of
              this parameter doesn't exist, then this operation SHALL
              fail with error-tag 'data-missing' and error-app-tag
              'routing-instance-not-found'.";
         }
         container destination-address {
           description
             "Network layer destination address.

              Address family specific modules MUST augment this
              container with a leaf named 'address'.";
           uses address-family;
         }
       }
       output {
         container route {
           description
             "The active route for the specified destination.

              If the routing instance has no active route for the
              destination address, no output is returned - the server
              SHALL send an <rpc-reply> containing a single element
              <ok>.

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

     rpc route-count {



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       description
         "Return the current number of routes in a RIB.";
       input {
         leaf rib-name {
           type rib-state-ref;
           mandatory "true";
           description
             "Name of the RIB.

              If the RIB with name equal to the value of this parameter
              doesn't exist, then this operation SHALL fail with
              error-tag 'data-missing' and error-app-tag
              'rib-not-found'.";
         }
       }
       output {
         leaf number-of-routes {
           type uint64;
           mandatory "true";
           description
             "Number of routes in the RIB.";
         }
       }
     }
   }

   <CODE ENDS>

8.  IPv4 Unicast Routing Management YANG Module

   RFC Editor: In this section, replace all occurrences of 'XXXX' with
   the actual RFC number and all occurrences of the revision date below
   with the date of RFC publication (and remove this note).

   <CODE BEGINS> file "ipv4-unicast-routing@2014-10-26.yang"

   module ietf-ipv4-unicast-routing {

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

     prefix "v4ur";

     import ietf-routing {
       prefix "rt";
     }

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



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     }

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

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

        WG Chair: Thomas Nadeau
                  <mailto:tnadeau@lucidvision.com>

        WG Chair: Juergen Schoenwaelder
                  <mailto:j.schoenwaelder@jacobs-university.de>

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

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

        Copyright (c) 2014 IETF Trust and the persons identified as
        authors of the code. All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Simplified BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

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

     revision 2014-10-26 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: A YANG Data Model for Routing Management";
     }

     /* Identities */

     identity ipv4-unicast {
       base rt:ipv4;
       description



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         "This identity represents the IPv4 unicast address family.";
     }

     /* Operational state data */

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route" {
       when "../../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 "../../../rt:address-family = 'v4ur:ipv4-unicast'" {
         description
           "This augment is valid only for IPv4 unicast.";
       }
       description
         "This leaf augments the 'simple-next-hop' case of IPv4 unicast
          routes.";
       leaf next-hop-address {
         type inet:ipv4-address;
         description
           "IPv4 address of the next-hop.";
       }
     }

     augment "/rt:routing-state/rt:next-hop-lists/rt:next-hop-list/"
           + "rt:next-hop/rt:next-hop-options/rt:simple-next-hop" {
       when "../rt:address-family = 'v4ur:ipv4-unicast'" {
         description
           "This augment is valid only for IPv4 unicast.";
       }
       description
         "This leaf augments next-hop list with IPv4 next-hop address.
          routes.";
       leaf next-hop-address {
         type inet:ipv4-address;
         description
           "IPv4 address of the next-hop.";



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       }
     }

     /* Configuration data */

     augment "/rt:routing/rt:routing-instance/rt:routing-protocols/"
           + "rt:routing-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";
           ordered-by "user";
           description
             "A user-ordered 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.";
             grouping next-hop-content {
               description
                 "Next-hop content for IPv4 unicast static routes.";
               uses rt:next-hop-content {
                 augment "next-hop-options" {
                   description
                     "Add next-hop address case.";
                   leaf next-hop-address {
                     type inet:ipv4-address;
                     description
                       "IPv4 address of the next-hop.";
                   }
                 }
               }
             }



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             choice simple-or-list {
               description
                 "Options for next-hops.";
               list multipath-entry {
                 if-feature rt:multipath-routes;
                 key "name";
                 description
                   "List of alternative next-hops.";
                 leaf name {
                   type string;
                   description
                     "A unique identifier of the next-hop entry.";
                 }
                 uses next-hop-content;
                 uses rt:next-hop-classifiers;
               }
               case simple-next-hop {
                 uses next-hop-content;
               }
             }
           }
         }
       }
     }

     /* RPC methods */

     augment "/rt:fib-route/rt:input/rt:destination-address" {
       when "rt:address-family='v4ur:ipv4-unicast'" {
         description
           "This augment is valid only for IPv4 unicast.";
       }
       description
         "This leaf augments the 'rt:destination-address' parameter of
          the 'rt:fib-route' operation.";
       leaf address {
         type inet:ipv4-address;
         description
           "IPv4 destination address.";
       }
     }

     augment "/rt:fib-route/rt:output/rt:route" {
       when "rt:address-family='v4ur:ipv4-unicast'" {
         description
           "This augment is valid only for IPv4 unicast.";
       }
       description



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         "This leaf augments the reply to the 'rt:fib-route'
          operation.";
       leaf destination-prefix {
         type inet:ipv4-prefix;
         description
           "IPv4 destination prefix.";
       }
     }

     augment "/rt:fib-route/rt:output/rt:route/rt:next-hop/"
           + "rt:next-hop-options/rt:simple-next-hop" {
       when "../rt:address-family='v4ur:ipv4-unicast'" {
         description
           "This augment is valid only for IPv4 unicast.";
       }
       description
         "This leaf augments the 'simple-next-hop' case in the reply to
          the 'rt:fib-route' operation.";
       leaf next-hop-address {
         type inet:ipv4-address;
         description
           "IPv4 address of the next-hop.";
       }
     }
   }

   <CODE ENDS>

9.  IPv6 Unicast Routing Management YANG Module

   RFC Editor: In this section, replace all occurrences of 'XXXX' with
   the actual RFC number and all occurrences of the revision date below
   with the date of RFC publication (and remove this note).

   <CODE BEGINS> file "ipv6-unicast-routing@2014-10-26.yang"

   module ietf-ipv6-unicast-routing {

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

     prefix "v6ur";

     import ietf-routing {
       prefix "rt";
     }

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



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     }

     import ietf-interfaces {
       prefix "if";
     }

     import ietf-ip {
       prefix "ip";
     }

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

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

        WG Chair: Thomas Nadeau
                  <mailto:tnadeau@lucidvision.com>

        WG Chair: Juergen Schoenwaelder
                  <mailto:j.schoenwaelder@jacobs-university.de>

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

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

        Copyright (c) 2014 IETF Trust and the persons identified as
        authors of the code. All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject to
        the license terms contained in, the Simplified BSD License set
        forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

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

     revision 2014-10-26 {
       description
         "Initial revision.";
       reference



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         "RFC XXXX: A YANG Data Model for Routing Management";
     }

     /* Identities */

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

     /* Operational state data */

     augment "/rt:routing-state/rt:routing-instance/rt:interfaces/"
           + "rt:interface" {
       description
         "IPv6-specific parameters of router interfaces.";
       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



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             "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



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              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.";
             }
             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.";
             }
             leaf autonomous-flag {
               type boolean;
               description



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                 "The value that is placed in the Autonomous Flag field
                  in the Prefix Information option.";
             }
           }
         }
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route" {
       when "../../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 "../../../rt:address-family = 'v6ur:ipv6-unicast'" {
         description
           "This augment is valid only for IPv6 unicast.";
       }
       description
         "This leaf augments the 'simple-next-hop' case of IPv6 unicast
          routes.";
       leaf next-hop {
         type inet:ipv6-address;
         description
           "IPv6 address of the next-hop.";
       }
     }

     augment "/rt:routing-state/rt:next-hop-lists/rt:next-hop-list/"
           + "rt:next-hop/rt:next-hop-options/rt:simple-next-hop" {
       when "../rt:address-family = 'v6ur:ipv6-unicast'" {
         description
           "This augment is valid only for IPv6 unicast.";
       }
       description
         "This leaf augments next-hop list with IPv6 next-hop address.
          routes.";
       leaf next-hop-address {



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         type inet:ipv6-address;
         description
           "IPv6 address of the next-hop.";
       }
     }

     /* Configuration data */

     augment
       "/rt:routing/rt:routing-instance/rt:interfaces/rt:interface" {
       when "/if:interfaces/if:interface[if:name=current()/rt:name]/"
          + "ip:ipv6/ip:enabled='true'" {
         description
           "This augment is only valid for router interfaces with
            enabled IPv6.";
       }
       description
         "Configuration of IPv6-specific parameters of router
          interfaces.";
       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 {



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             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.



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              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";
         }



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         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
                 "The prefix either may be explicitly removed from the



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                  set of advertised prefixes, or parameters with which
                  it is advertised may be 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



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                      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.";
                 }
               }
             }
           }
         }
       }
     }

     augment "/rt:routing/rt:routing-instance/rt:routing-protocols/"
           + "rt:routing-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";
           ordered-by "user";
           description
             "A user-ordered 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 {



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             description
               "Configuration of next-hop.";
             grouping next-hop-content {
               description
                 "Next-hop content for IPv6 unicast static routes.";
               uses rt:next-hop-content {
                 augment "next-hop-options" {
                   description
                     "Add next-hop address case.";
                   leaf next-hop-address {
                     type inet:ipv6-address;
                     description
                       "IPv6 address of the next-hop.";
                   }
                 }
               }
             }
             choice simple-or-list {
               description
                 "Options for next-hops.";
               list multipath-entry {
                 if-feature rt:multipath-routes;
                 key "name";
                 description
                   "List of alternative next-hops.";
                 leaf name {
                   type string;
                   description
                     "A unique identifier of the next-hop entry.";
                 }
                 uses next-hop-content;
                 uses rt:next-hop-classifiers;
               }
               case simple-next-hop {
                 uses next-hop-content;
               }
             }
           }
         }
       }
     }

     /* RPC methods */

     augment "/rt:fib-route/rt:input/rt:destination-address" {
       when "rt:address-family='v6ur:ipv6-unicast'" {
         description
           "This augment is valid only for IPv6 unicast.";



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       }
       description
         "This leaf augments the 'rt:destination-address' parameter of
          the 'rt:fib-route' operation.";
       leaf address {
         type inet:ipv6-address;
         description
           "IPv6 destination address.";
       }
     }

     augment "/rt:fib-route/rt:output/rt:route" {
       when "rt:address-family='v6ur:ipv6-unicast'" {
         description
           "This augment is valid only for IPv6 unicast.";
       }
       description
         "This leaf augments the reply to the 'rt:fib-route'
          operation.";
       leaf destination-prefix {
         type inet:ipv6-prefix;
         description
           "IPv6 destination prefix.";
       }
     }

     augment "/rt:fib-route/rt:output/rt:route/rt:next-hop/"
           + "rt:next-hop-options/rt:simple-next-hop" {
       when "../rt:address-family='v4ur:ipv6-unicast'" {
         description
           "This augment is valid only for IPv6 unicast.";
       }
       description
         "This leaf augments the 'simple-next-hop' case in the reply to
          the 'rt:fib-route' operation.";
       leaf next-hop-address {
         type inet:ipv6-address;
         description
           "IPv6 address of the next-hop.";
       }
     }
   }

   <CODE ENDS>







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10.  IANA Considerations

   RFC Ed.: In this section, replace all occurrences of 'XXXX' with the
   actual RFC number (and remove this note).

   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]:

















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   -------------------------------------------------------------------
   name:         ietf-routing
   namespace:    urn:ietf:params:xml:ns:yang:ietf-routing
   prefix:       rt
   reference:    RFC XXXX
   -------------------------------------------------------------------

   -------------------------------------------------------------------
   name:         ietf-ipv4-unicast-routing
   namespace:    urn:ietf:params:xml:ns:yang:ietf-ipv4-unicast-routing
   prefix:       v4ur
   reference:    RFC XXXX
   -------------------------------------------------------------------

   -------------------------------------------------------------------
   name:         ietf-ipv6-unicast-routing
   namespace:    urn:ietf:params:xml:ns:yang:ietf-ipv6-unicast-routing
   prefix:       v6ur
   reference:    RFC XXXX
   -------------------------------------------------------------------

11.  Security Considerations

   Configuration and state data conforming to the core routing data
   model (defined in this document) are designed to be accessed via the
   NETCONF protocol [RFC6241].  The lowest NETCONF layer is the secure
   transport layer and the mandatory-to-implement secure transport is
   SSH [RFC6242].  The NETCONF access control model [RFC6536] provides
   the means to restrict access for particular NETCONF users to a pre-
   configured subset of all available NETCONF protocol operations and
   content.

   A number of data nodes defined in the YANG modules belonging to the
   configuration part of 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", can have negative effects on
   the network if the protocol operations are not properly protected.

   The vulnerable "config true" subtrees and data nodes are the
   following:

   /routing/routing-instance/interfaces/interface:  This list assigns a
      network layer interface to a routing instance and may also specify
      interface parameters related to routing.





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

   /routing/route-filters/route-filter:  This list specifies the
      configured route filters which represent administrative policies
      for redistributing and modifying routing information.

   /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.  Acknowledgments

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

13.  References

13.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

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

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





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

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

   [RFC7277]  Bjorklund, M., "A YANG Data Model for IP Management", RFC
              7277, June 2014.

13.2.  Informative References

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, February 2006.

   [RFC6087]  Bierman, A., "Guidelines for Authors and Reviewers of YANG
              Data Model Documents", RFC 6087, January 2011.

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

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

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.  Data type of
   every leaf node is shown near the right end of the corresponding
   line.

A.1.  Configuration Data

   +--rw routing
      +--rw routing-instance* [name]
      |  +--rw name                 string
      |  +--rw type?                identityref
      |  +--rw enabled?             boolean
      |  +--rw router-id?           yang:dotted-quad
      |  +--rw description?         string
      |  +--rw default-ribs {multiple-ribs}?
      |  |  +--rw default-rib* [address-family]
      |  |     +--rw address-family    identityref
      |  |     +--rw rib-name          string
      |  +--rw interfaces
      |  |  +--rw interface* [name]



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      |  |     +--rw name                             if:interface-ref
      |  |     +--rw v6ur:ipv6-router-advertisements
      |  |        +--rw v6ur:send-advertisements?    boolean
      |  |        +--rw v6ur:max-rtr-adv-interval?   uint16
      |  |        +--rw v6ur:min-rtr-adv-interval?   uint16
      |  |        +--rw v6ur:managed-flag?           boolean
      |  |        +--rw v6ur:other-config-flag?      boolean
      |  |        +--rw v6ur:link-mtu?               uint32
      |  |        +--rw v6ur:reachable-time?         uint32
      |  |        +--rw v6ur:retrans-timer?          uint32
      |  |        +--rw v6ur:cur-hop-limit?          uint8
      |  |        +--rw v6ur:default-lifetime?       uint16
      |  |        +--rw v6ur:prefix-list
      |  |           +--rw v6ur:prefix* [prefix-spec]
      |  |              +--rw v6ur:prefix-spec        inet:ipv6-prefix
      |  |              +--rw (control-adv-prefixes)?
      |  |                 +--:(no-advertise)
      |  |                 |  +--rw v6ur:no-advertise?         empty
      |  |                 +--:(advertise)
      |  |                    +--rw v6ur:valid-lifetime?       uint32
      |  |                    +--rw v6ur:on-link-flag?         boolean
      |  |                    +--rw v6ur:preferred-lifetime?   uint32
      |  |                    +--rw v6ur:autonomous-flag?      boolean
      |  +--rw routing-protocols
      |     +--rw routing-protocol* [type name]
      |        +--rw type                identityref
      |        +--rw name                string
      |        +--rw description?        string
      |        +--rw enabled?            boolean
      |        +--rw route-preference?   route-preference
      |        +--rw connected-ribs
      |        |  +--rw connected-rib* [rib-name]
      |        |     +--rw rib-name         rib-ref
      |        |     +--rw import-filter?   route-filter-ref
      |        |     +--rw export-filter?   route-filter-ref
      |        +--rw static-routes
      |           +--rw v4ur:ipv4
      |           |  +--rw v4ur:route* [destination-prefix]
      |           |     +--rw v4ur:destination-prefix inet:ipv4-prefix
      |           |     +--rw v4ur:description?          string
      |           |     +--rw v4ur:next-hop
      |           |        +--rw (simple-or-list)?
      |           |           +--:(multipath-entry)
      |           |           |  +--rw v4ur:multipath-entry* [name]
      |           |           |     +--rw v4ur:name             string
      |           |           |     +--rw (next-hop-options)
      |           |           |     |  +--:(simple-next-hop)
      |           |           |     |  |  +--rw v4ur:outgoing-interface?



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      |           |           |     |  +--:(special-next-hop)
      |           |           |     |  |  +--rw v4ur:special-next-hop?
      |           |           |     |  +--:(next-hop-address)
      |           |           |     |     +--rw v4ur:next-hop-address?
      |           |           |     +--rw v4ur:priority?
      |           |           |     +--rw v4ur:weight?           uint8
      |           |           +--:(simple-next-hop)
      |           |              +--rw (next-hop-options)
      |           |                 +--:(simple-next-hop)
      |           |                 |  +--rw v4ur:outgoing-interface?
      |           |                 +--:(special-next-hop)
      |           |                 |  +--rw v4ur:special-next-hop?
      |           |                 +--:(next-hop-address)
      |           |                    +--rw v4ur:next-hop-address?
      |           +--rw v6ur:ipv6
      |              +--rw v6ur:route* [destination-prefix]
      |                 +--rw v6ur:destination-prefix inet:ipv6-prefix
      |                 +--rw v6ur:description?          string
      |                 +--rw v6ur:next-hop
      |                    +--rw (simple-or-list)?
      |                       +--:(multipath-entry)
      |                       |  +--rw v6ur:multipath-entry* [name]
      |                       |     +--rw v6ur:name             string
      |                       |     +--rw (next-hop-options)
      |                       |     |  +--:(simple-next-hop)
      |                       |     |  |  +--rw v6ur:outgoing-interface?
      |                       |     |  +--:(special-next-hop)
      |                       |     |  |  +--rw v6ur:special-next-hop?
      |                       |     |  +--:(next-hop-address)
      |                       |     |     +--rw v6ur:next-hop-address?
      |                       |     +--rw v6ur:priority?
      |                       |     +--rw v6ur:weight?           uint8
      |                       +--:(simple-next-hop)
      |                          +--rw (next-hop-options)
      |                             +--:(simple-next-hop)
      |                             |  +--rw v6ur:outgoing-interface?
      |                             +--:(special-next-hop)
      |                             |  +--rw v6ur:special-next-hop?
      |                             +--:(next-hop-address)
      |                                +--rw v6ur:next-hop-address?
      +--rw ribs
      |  +--rw rib* [name]
      |     +--rw name              string
      |     +--rw address-family    identityref
      |     +--rw description?      string
      |     +--rw recipient-ribs {multiple-ribs}?
      |        +--rw recipient-rib* [rib-name]
      |           +--rw rib-name    rib-ref



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      |           +--rw filter?     route-filter-ref
      +--rw route-filters
         +--rw route-filter* [name]
            +--rw name           string
            +--rw description?   string
            +--rw type           identityref

A.2.  State Data

   +--ro routing-state
      +--ro routing-instance* [name]
      |  +--ro name                 string
      |  +--ro id                   uint64
      |  +--ro type?                identityref
      |  +--ro default-ribs
      |  |  +--ro default-rib* [address-family]
      |  |     +--ro address-family    identityref
      |  |     +--ro rib-name          rib-state-ref
      |  +--ro interfaces
      |  |  +--ro interface* [name]
      |  |     +--ro name                        if:interface-state-ref
      |  |     +--ro v6ur:ipv6-router-advertisements
      |  |        +--ro v6ur:send-advertisements?    boolean
      |  |        +--ro v6ur:max-rtr-adv-interval?   uint16
      |  |        +--ro v6ur:min-rtr-adv-interval?   uint16
      |  |        +--ro v6ur:managed-flag?           boolean
      |  |        +--ro v6ur:other-config-flag?      boolean
      |  |        +--ro v6ur:link-mtu?               uint32
      |  |        +--ro v6ur:reachable-time?         uint32
      |  |        +--ro v6ur:retrans-timer?          uint32
      |  |        +--ro v6ur:cur-hop-limit?          uint8
      |  |        +--ro v6ur:default-lifetime?       uint16
      |  |        +--ro v6ur:prefix-list
      |  |           +--ro v6ur:prefix* [prefix-spec]
      |  |              +--ro v6ur:prefix-spec        inet:ipv6-prefix
      |  |              +--ro v6ur:valid-lifetime?       uint32
      |  |              +--ro v6ur:on-link-flag?         boolean
      |  |              +--ro v6ur:preferred-lifetime?   uint32
      |  |              +--ro v6ur:autonomous-flag?      boolean
      |  +--ro routing-protocols
      |     +--ro routing-protocol* [type name]
      |        +--ro type                identityref
      |        +--ro name                string
      |        +--ro route-preference    route-preference
      |        +--ro connected-ribs
      |           +--ro connected-rib* [rib-name]
      |              +--ro rib-name         rib-state-ref
      |              +--ro import-filter?   route-filter-state-ref



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      |              +--ro export-filter?   route-filter-state-ref
      +--ro next-hop-lists
      |  +--ro next-hop-list* [id]
      |     +--ro id                uint64
      |     +--ro address-family    identityref
      |     +--ro next-hop*
      |        +--ro (next-hop-options)
      |        |  +--:(next-hop-list)
      |        |  |  +--ro next-hop-list?           next-hop-list-ref
      |        |  +--:(use-rib)
      |        |  |  +--ro use-rib?                 rib-state-ref
      |        |  +--:(simple-next-hop)
      |        |  |  +--ro outgoing-interface?
      |        |  |  +--ro v4ur:next-hop-address?   inet:ipv4-address
      |        |  |  +--ro v6ur:next-hop-address?   inet:ipv6-address
      |        |  +--:(special-next-hop)
      |        |     +--ro special-next-hop?        enumeration
      |        +--ro priority?                enumeration
      |        +--ro weight?                  uint8
      +--ro ribs
      |  +--ro rib* [name]
      |     +--ro name              string
      |     +--ro id                uint64
      |     +--ro address-family    identityref
      |     +--ro routes
      |     |  +--ro route*
      |     |     +--ro route-preference?          route-preference
      |     |     +--ro next-hop
      |     |     |  +--ro (next-hop-options)
      |     |     |     +--:(next-hop-list)
      |     |     |     |  +--ro next-hop-list?      next-hop-list-ref
      |     |     |     +--:(use-rib)
      |     |     |     |  +--ro use-rib?                rib-state-ref
      |     |     |     +--:(simple-next-hop)
      |     |     |     |  +--ro outgoing-interface?
      |     |     |     |  +--ro v4ur:next-hop-address?
      |     |     |     |  +--ro v6ur:next-hop?
      |     |     |     +--:(special-next-hop)
      |     |     |        +--ro special-next-hop?        enumeration
      |     |     +--ro source-protocol            identityref
      |     |     +--ro active?                    empty
      |     |     +--ro last-updated?              yang:date-and-time
      |     |     +--ro v4ur:destination-prefix?   inet:ipv4-prefix
      |     |     +--ro v6ur:destination-prefix?   inet:ipv6-prefix
      |     +--ro recipient-ribs
      |        +--ro recipient-rib* [rib-name]
      |           +--ro rib-name    rib-state-ref
      |           +--ro filter?     route-filter-state-ref



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      +--ro route-filters
         +--ro route-filter* [name]
            +--ro name    string
            +--ro type    identityref

Appendix B.  Minimum Implementation

   Some parts and options of the core routing model, such as route
   filters or multiple routing tables, 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 will provide a single system-controlled
   routing instance, and will not allow clients to create any user-
   controlled instances.

   Typically, neither of the features defined in the "ietf-routing"
   module ("multiple-ribs" and "multipath-routes") will be supported.
   This means that:

   o  A single system-controlled RIB (routing table) is available for
      each supported address family - IPv4, IPv6 or both.  These RIBs
      are the default RIBs, so references to them will also appear as
      system-controlled entries of the "default-rib" list in state data.
      No user-controlled RIBs are allowed.

   o  Each route has no more than one "next-hop", "outgoing-interface"
      or "special-next-hop".

   In addition to the mandatory instance of the "direct" pseudo-
   protocol, a minimum implementation should support configured
   instance(s) of the "static" pseudo-protocol.  Even with a single RIB
   per address family, it may be occasionally useful to be able to
   configure multiple "static" instances.  For example, a client may
   want to configure alternative sets of static routes and activate or
   deactivate them by means of configuring appropriate route filters
   ("allow-all-route-filter" or "deny-all-route-filter").

   Platforms with severely constrained resources may use deviations for
   restricting the data model, e.g., limiting the number of "static"
   routing protocol instances, preventing any route filters to be
   configured etc.








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Appendix C.  Example: Adding a New Routing Protocol

   This appendix demonstrates how the core routing data model can be
   extended to support a new routing protocol.  The YANG module
   "example-rip" shown below is intended only as an illustration rather
   than a real definition of a data model for the RIP routing protocol.
   For the sake of brevity, this module does not obey all the guidelines
   specified in [RFC6087].  See also Section 5.4.2.

   module example-rip {

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

     prefix "rip";

     import ietf-routing {
       prefix "rt";
     }

     identity rip {
       base rt:routing-protocol;
       description
         "Identity for the RIP routing protocol.";
     }

     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. AS
            number.";
       }
     }

     augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route" {
       when "rt:source-protocol = 'rip:rip'" {



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         description
           "This augment is only valid for a routes whose source
            protocol is RIP.";
       }
       description
         "RIP-specific route attributes.";
       uses route-content;
     }

     augment "/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:routing-instance/rt:routing-protocols/"
           + "rt:routing-protocol" {
       when "rt:type = 'rip:rip'" {
         description
           "This augment is only valid for a routing protocol instance
            of type 'rip'.";
       }
       container rip {
         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 leafref {
                 path "../../../../../../rt:interfaces/rt:interface/"
                    + "rt:name";
               }
             }
             leaf enabled {
               type boolean;
               default "true";
             }
             leaf metric {
               type rip-metric;
               default "1";



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             }
           }
         }
         leaf update-interval {
           type uint8 {
             range "10..60";
           }
           units "seconds";
           default "30";
           description
             "Time interval between periodic updates.";
         }
       }
     }
   }

Appendix D.  Example: NETCONF <get> Reply

   This section contains a sample reply to the NETCONF <get> message,
   which could be sent by a server supporting (i.e., advertising them in
   the NETCONF <hello> message) the following YANG modules:

   o  ietf-interfaces [RFC7223],

   o  ietf-ip [RFC7277],

   o  ietf-routing (Section 7),

   o  ietf-ipv4-unicast-routing (Section 8),

   o  ietf-ipv6-unicast-routing (Section 9).

   We assume a simple network set-up as shown in Figure 5: 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.















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                   +-----------------+
                   |                 |
                   |    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 5: Example network configuration

   A reply to the NETCONF <get> message sent by router "A" would then be
   as follows:

  <?xml version="1.0"?>
  <rpc-reply
      message-id="101"
      xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
      xmlns:v4ur="urn:ietf:params:xml:ns:yang:ietf-ipv4-unicast-routing"
      xmlns:v6ur="urn:ietf:params:xml:ns:yang:ietf-ipv6-unicast-routing"
      xmlns:if="urn:ietf:params:xml:ns:yang:ietf-interfaces"
      xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type"
      xmlns:ip="urn:ietf:params:xml:ns:yang:ietf-ip"
      xmlns:rt="urn:ietf:params:xml:ns:yang:ietf-routing">
   <data>
    <if:interfaces>
     <if:interface>
      <if:name>eth0</if:name>
      <if:type>ianaift:ethernetCsmacd</if:type>
      <if:description>
       Uplink to ISP.
      </if:description>
      <ip:ipv4>
       <ip:address>
        <ip:ip>192.0.2.1</ip:ip>
        <ip:prefix-length>24</ip:prefix-length>
       </ip:address>



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       <ip:forwarding>true</ip:forwarding>
      </ip:ipv4>
      <ip:ipv6>
       <ip:address>
        <ip:ip>2001:0db8:0:1::1</ip:ip>
        <ip:prefix-length>64</ip:prefix-length>
       </ip:address>
       <ip:forwarding>true</ip:forwarding>
       <ip:autoconf>
        <ip:create-global-addresses>false</ip:create-global-addresses>
       </ip:autoconf>
      </ip:ipv6>
     </if:interface>
     <if:interface>
      <if:name>eth1</if:name>
      <if:type>ianaift:ethernetCsmacd</if:type>
      <if:description>
       Interface to the internal network.
      </if:description>
      <ip:ipv4>
       <ip:address>
        <ip:ip>198.51.100.1</ip:ip>
        <ip:prefix-length>24</ip:prefix-length>
       </ip:address>
       <ip:forwarding>true</ip:forwarding>
      </ip:ipv4>
      <ip:ipv6>
       <ip:address>
        <ip:ip>2001:0db8:0:2::1</ip:ip>
        <ip:prefix-length>64</ip:prefix-length>
       </ip:address>
       <ip:forwarding>true</ip:forwarding>
       <ip:autoconf>
        <ip:create-global-addresses>false</ip:create-global-addresses>
       </ip:autoconf>
      </ip:ipv6>
     </if:interface>
    </if:interfaces>
    <if:interfaces-state>
     <if:interface>
      <if:name>eth0</if:name>
      <if:type>ianaift:ethernetCsmacd</if:type>
      <if:phys-address>00:0C:42:E5:B1:E9</if:phys-address>
      <if:oper-status>up</if:oper-status>
      <if:statistics>
        <if:discontinuity-time>
      2014-10-24T17:11:27+00:58
        </if:discontinuity-time>



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      </if:statistics>
      <ip:ipv4>
       <ip:forwarding>true</ip:forwarding>
       <ip:mtu>1500</ip:mtu>
       <ip:address>
        <ip:ip>192.0.2.1</ip:ip>
        <ip:prefix-length>24</ip:prefix-length>
       </ip:address>
      </ip:ipv4>
      <ip:ipv6>
       <ip:forwarding>true</ip:forwarding>
       <ip:mtu>1500</ip:mtu>
       <ip:address>
        <ip:ip>2001:0db8:0:1::1</ip:ip>
        <ip:prefix-length>64</ip:prefix-length>
       </ip:address>
      </ip:ipv6>
     </if:interface>
     <if:interface>
      <if:name>eth1</if:name>
      <if:type>ianaift:ethernetCsmacd</if:type>
      <if:oper-status>up</if:oper-status>
      <if:phys-address>00:0C:42:E5:B1:EA</if:phys-address>
      <if:statistics>
        <if:discontinuity-time>
      2014-10-24T17:11:27+00:59
        </if:discontinuity-time>
      </if:statistics>
      <ip:ipv4>
       <ip:forwarding>true</ip:forwarding>
       <ip:mtu>1500</ip:mtu>
       <ip:address>
        <ip:ip>198.51.100.1</ip:ip>
        <ip:prefix-length>24</ip:prefix-length>
       </ip:address>
      </ip:ipv4>
      <ip:ipv6>
       <ip:forwarding>true</ip:forwarding>
       <ip:mtu>1500</ip:mtu>
       <ip:address>
        <ip:ip>2001:0db8:0:2::1</ip:ip>
        <ip:prefix-length>64</ip:prefix-length>
       </ip:address>
      </ip:ipv6>
     </if:interface>
    </if:interfaces-state>
    <rt:routing>
     <rt:routing-instance>



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      <rt:name>rtr0</rt:name>
      <rt:description>Router A</rt:description>
      <rt:interfaces>
       <rt:interface>
        <rt:name>eth1</rt:name>
        <v6ur:ipv6-router-advertisements>
         <v6ur:send-advertisements>true</v6ur:send-advertisements>
         <v6ur:prefix-list>
          <v6ur:prefix>
           <v6ur:prefix-spec>2001:db8:0:2::/64</v6ur:prefix-spec>
          </v6ur:prefix>
         </v6ur:prefix-list>
        </v6ur:ipv6-router-advertisements>
       </rt:interface>
      </rt:interfaces>
      <rt:routing-protocols>
       <rt:routing-protocol>
        <rt:type>rt:static</rt:type>
        <rt:name>st0</rt:name>
        <rt:description>
         Static routing is used for the internal network.
        </rt:description>
        <rt:static-routes>
         <v4ur:ipv4>
          <v4ur:route>
           <v4ur:destination-prefix>0.0.0.0/0</v4ur:destination-prefix>
           <v4ur:next-hop>
        <v4ur:next-hop-address>192.0.2.2</v4ur:next-hop-address>
       </v4ur:next-hop>
          </v4ur:route>
         </v4ur:ipv4>
         <v6ur:ipv6>
          <v6ur:route>
           <v6ur:destination-prefix>::/0</v6ur:destination-prefix>
           <v6ur:next-hop>
        <v6ur:next-hop-address>2001:db8:0:1::2</v6ur:next-hop-address>
       </v6ur:next-hop>
          </v6ur:route>
         </v6ur:ipv6>
        </rt:static-routes>
       </rt:routing-protocol>
      </rt:routing-protocols>
     </rt:routing-instance>
    </rt:routing>
    <rt:routing-state>
     <rt:routing-instance>
      <rt:name>rtr0</rt:name>
      <rt:id>2718281828</rt:id>



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      <rt:default-ribs>
       <rt:default-rib>
        <rt:address-family>v4ur:ipv4-unicast</rt:address-family>
        <rt:rib-name>ipv4-master</rt:rib-name>
       </rt:default-rib>
       <rt:default-rib>
        <rt:address-family>v6ur:ipv6-unicast</rt:address-family>
        <rt:rib-name>ipv6-master</rt:rib-name>
       </rt:default-rib>
      </rt:default-ribs>
      <rt:interfaces>
       <rt:interface>
        <rt:name>eth0</rt:name>
       </rt:interface>
       <rt:interface>
        <rt:name>eth1</rt:name>
        <v6ur:ipv6-router-advertisements>
         <v6ur:send-advertisements>true</v6ur:send-advertisements>
         <v6ur:prefix-list>
          <v6ur:prefix>
           <v6ur:prefix-spec>2001:db8:0:2::/64</v6ur:prefix-spec>
          </v6ur:prefix>
         </v6ur:prefix-list>
        </v6ur:ipv6-router-advertisements>
       </rt:interface>
      </rt:interfaces>
      <rt:routing-protocols>
       <rt:routing-protocol>
        <rt:type>rt:static</rt:type>
        <rt:name>st0</rt:name>
        <rt:route-preference>5</rt:route-preference>
       </rt:routing-protocol>
      </rt:routing-protocols>
     </rt:routing-instance>
     <rt:ribs>
      <rt:rib>
       <rt:name>ipv4-master</rt:name>
       <rt:id>897932384</rt:id>
       <rt:address-family>v4ur:ipv4-unicast</rt:address-family>
       <rt:routes>
        <rt:route>
         <v4ur:destination-prefix>192.0.2.1/24</v4ur:destination-prefix>
         <rt:next-hop>
      <rt:outgoing-interface>eth0</rt:outgoing-interface>
         </rt:next-hop>
         <rt:route-preference>0</rt:route-preference>
         <rt:source-protocol>rt:direct</rt:source-protocol>
         <rt:last-updated>



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       2014-10-24T17:11:27+01:00
         </rt:last-updated>
        </rt:route>
        <rt:route>
      <v4ur:destination-prefix>
        198.51.100.0/24
      </v4ur:destination-prefix>
         <rt:next-hop>
      <rt:outgoing-interface>eth1</rt:outgoing-interface>
         </rt:next-hop>
         <rt:source-protocol>rt:direct</rt:source-protocol>
         <rt:route-preference>0</rt:route-preference>
         <rt:last-updated>
       2014-10-24T17:11:27+01:00
         </rt:last-updated>
        </rt:route>
        <rt:route>
         <v4ur:destination-prefix>0.0.0.0/0</v4ur:destination-prefix>
         <rt:source-protocol>rt:static</rt:source-protocol>
         <rt:route-preference>5</rt:route-preference>
         <rt:next-hop>
      <v4ur:next-hop-address>192.0.2.2</v4ur:next-hop-address>
         </rt:next-hop>
         <rt:last-updated>
       2014-10-24T18:02:45+01:00
         </rt:last-updated>
        </rt:route>
       </rt:routes>
      </rt:rib>
      <rt:rib>
       <rt:name>ipv6-master</rt:name>
       <rt:id>751058209</rt:id>
       <rt:address-family>v6ur:ipv6-unicast</rt:address-family>
       <rt:routes>
        <rt:route>
      <v6ur:destination-prefix>
        2001:db8:0:1::/64
      </v6ur:destination-prefix>
         <rt:next-hop>
      <rt:outgoing-interface>eth0</rt:outgoing-interface>
         </rt:next-hop>
         <rt:source-protocol>rt:direct</rt:source-protocol>
         <rt:route-preference>0</rt:route-preference>
         <rt:last-updated>
       2014-10-24T17:11:27+01:00
         </rt:last-updated>
        </rt:route>
        <rt:route>



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      <v6ur:destination-prefix>
        2001:db8:0:2::/64
      </v6ur:destination-prefix>
         <rt:next-hop>
      <rt:outgoing-interface>eth1</rt:outgoing-interface>
         </rt:next-hop>
         <rt:source-protocol>rt:direct</rt:source-protocol>
         <rt:route-preference>0</rt:route-preference>
         <rt:last-updated>
       2014-10-24T17:11:27+01:00
         </rt:last-updated>
        </rt:route>
        <rt:route>
         <v6ur:destination-prefix>::/0</v6ur:destination-prefix>
         <rt:next-hop>
      <v6ur:next-hop>2001:db8:0:1::2</v6ur:next-hop>
         </rt:next-hop>
         <rt:source-protocol>rt:static</rt:source-protocol>
         <rt:route-preference>5</rt:route-preference>
         <rt:last-updated>
       2014-10-24T18:02:45+01:00
         </rt:last-updated>
        </rt:route>
       </rt:routes>
      </rt:rib>
     </rt:ribs>
    </rt:routing-state>
   </data>
  </rpc-reply>

Appendix E.  Change Log

   RFC Editor: Remove this section upon publication as an RFC.

E.1.  Changes Between Versions -15 and -16

   o  Added 'type' as the second key component of 'routing-protocol',
      both in configuration and state data.

   o  The restriction of no more than one connected RIB per address
      family was removed.

   o  Removed the 'id' key of routes in RIBs.  This list has no keys
      anymore.

   o  Remove the 'id' key from static routes and make 'destination-
      prefix' the only key.




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   o  Added 'route-preference' as a new attribute of routes in RIB.

   o  Added 'active' as a new attribute of routes in RIBs.

   o  Renamed RPC operation 'active-route' to 'fib-route.

   o  Added 'route-preference' as a new parameter of routing protocol
      instances, both in configuration and state data.

   o  Renamed identity 'rt:standard-routing-instance' to 'rt:default-
      routing-instance'.

   o  Added next-hop lists to state data.

   o  Added two cases for specifying next-hops indirectly - via a new
      RIB or a recursive list of next-hops.

   o  Reorganized next-hop in static routes.

   o  Removed all 'if-feature' statements from state data.

E.2.  Changes Between Versions -14 and -15

   o  Removed all defaults from state data.

   o  Removed default from 'cur-hop-limit' in config.

E.3.  Changes Between Versions -13 and -14

   o  Removed dependency of 'connected-ribs' on the 'multiple-ribs'
      feature.

   o  Removed default value of 'cur-hop-limit' in state data.

   o  Moved parts of descriptions and all references on IPv6 RA
      parameters from state data to configuration.

   o  Added reference to RFC 6536 in the Security section.

E.4.  Changes Between Versions -12 and -13

   o  Wrote appendix about minimum implementation.

   o  Remove "when" statement for IPv6 router interface state data - it
      was dependent on a config value that may not be present.

   o  Extra container for the next-hop list.




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   o  Names rather than numeric ids are used for referring to list
      entries in state data.

   o  Numeric ids are always declared as mandatory and unique.  Their
      description states that they are ephemeral.

   o  Descriptions of "name" keys in state data lists are required to be
      persistent.

   o

   o  Removed "if-feature multiple-ribs;" from connected-ribs.

   o  "rib-name" instead of "name" is used as the name of leafref nodes.

   o  "next-hop" instead of "nexthop" or "gateway" used throughout, both
      in node names and text.

E.5.  Changes Between Versions -11 and -12

   o  Removed feature "advanced-router" and introduced two features
      instead: "multiple-ribs" and "multipath-routes".

   o  Unified the keys of config and state versions of "routing-
      instance" and "rib" lists.

   o  Numerical identifiers of state list entries are not keys anymore,
      but they are constrained using the "unique" statement.

   o  Updated acknowledgements.

E.6.  Changes Between Versions -10 and -11

   o  Migrated address families from IANA enumerations to identities.

   o  Terminology and node names aligned with the I2RS RIB model: router
      -> routing instance, routing table -> RIB.

   o  Introduced uint64 keys for state lists: routing-instance, rib,
      route, nexthop.

   o  Described the relationship between system-controlled and user-
      controlled list entries.

   o  Feature "user-defined-routing-tables" changed into "advanced-
      router".





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   o  Made nexthop into a choice in order to allow for nexthop-list
      (I2RS requirement).

   o  Added nexthop-list with entries having priorities (backup) and
      weights (load balancing).

   o  Updated bibliography references.

E.7.  Changes Between Versions -09 and -10

   o  Added subtree for state data ("/routing-state").

   o  Terms "system-controlled entry" and "user-controlled entry"
      defined and used.

   o  New feature "user-defined-routing-tables".  Nodes that are useful
      only with user-defined routing tables are now conditional.

   o  Added grouping "router-id".

   o  In routing tables, "source-protocol" attribute of routes now
      reports only protocol type, and its datatype is "identityref".

   o  Renamed "main-routing-table" to "default-routing-table".

E.8.  Changes Between Versions -08 and -09

   o  Fixed "must" expresion for "connected-routing-table".

   o  Simplified "must" expression for "main-routing-table".

   o  Moved per-interface configuration of a new routing protocol under
      'routing-protocol'.  This also affects the 'example-rip' module.

E.9.  Changes Between Versions -07 and -08

   o  Changed reference from RFC6021 to RFC6021bis.

E.10.  Changes Between Versions -06 and -07

   o  The contents of <get-reply> in Appendix D was updated: "eth[01]"
      is used as the value of "location", and "forwarding" is on for
      both interfaces and both IPv4 and IPv6.

   o  The "must" expression for "main-routing-table" was modified to
      avoid redundant error messages reporting address family mismatch
      when "name" points to a non-existent routing table.




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   o  The default behavior for IPv6 RA prefix advertisements was
      clarified.

   o  Changed type of "rt:router-id" to "ip:dotted-quad".

   o  Type of "rt:router-id" changed to "yang:dotted-quad".

   o  Fixed missing prefixes in XPath expressions.

E.11.  Changes Between Versions -05 and -06

   o  Document title changed: "Configuration" was replaced by
      "Management".

   o  New typedefs "routing-table-ref" and "route-filter-ref".

   o  Double slashes "//" were removed from XPath expressions and
      replaced with the single "/".

   o  Removed uniqueness requirement for "router-id".

   o  Complete data tree is now in Appendix A.

   o  Changed type of "source-protocol" from "leafref" to "string".

   o  Clarified the relationship between routing protocol instances and
      connected routing tables.

   o  Added a must constraint saying that a routing table connected to
      the direct pseudo-protocol must not be a main routing table.

E.12.  Changes Between Versions -04 and -05

   o  Routing tables are now global, i.e., "routing-tables" is a child
      of "routing" rather than "router".

   o  "must" statement for "static-routes" changed to "when".

   o  Added "main-routing-tables" containing references to main routing
      tables for each address family.

   o  Removed the defaults for "address-family" and "safi" and made them
      mandatory.

   o  Removed the default for route-filter/type and made this leaf
      mandatory.





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   o  If there is no active route for a given destination, the "active-
      route" RPC returns no output.

   o  Added "enabled" switch under "routing-protocol".

   o  Added "router-type" identity and "type" leaf under "router".

   o  Route attribute "age" changed to "last-updated", its type is
      "yang:date-and-time".

   o  The "direct" pseudo-protocol is always connected to main routing
      tables.

   o  Entries in the list of connected routing tables renamed from
      "routing-table" to "connected-routing-table".

   o  Added "must" constraint saying that a routing table must not be
      its own recipient.

E.13.  Changes Between Versions -03 and -04

   o  Changed "error-tag" for both RPC methods from "missing element" to
      "data-missing".

   o  Removed the decrementing behavior for advertised IPv6 prefix
      parameters "valid-lifetime" and "preferred-lifetime".

   o  Changed the key of the static route lists from "seqno" to "id"
      because the routes needn't be sorted.

   o  Added 'must' constraint saying that "preferred-lifetime" must not
      be greater than "valid-lifetime".

E.14.  Changes Between Versions -02 and -03

   o  Module "iana-afn-safi" moved to I-D "iana-if-type".

   o  Removed forwarding table.

   o  RPC "get-route" changed to "active-route".  Its output is a list
      of routes (for multi-path routing).

   o  New RPC "route-count".

   o  For both RPCs, specification of negative responses was added.

   o  Relaxed separation of router instances.




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   o  Assignment of interfaces to router instances needn't be disjoint.

   o  Route filters are now global.

   o  Added "allow-all-route-filter" for symmetry.

   o  Added Section 6 about interactions with "ietf-interfaces" and
      "ietf-ip".

   o  Added "router-id" leaf.

   o  Specified the names for IPv4/IPv6 unicast main routing tables.

   o  Route parameter "last-modified" changed to "age".

   o  Added container "recipient-routing-tables".

E.15.  Changes Between Versions -01 and -02

   o  Added module "ietf-ipv6-unicast-routing".

   o  The example in Appendix D now uses IP addresses from blocks
      reserved for documentation.

   o  Direct routes appear by default in the forwarding table.

   o  Network layer interfaces must be assigned to a router instance.
      Additional interface configuration may be present.

   o  The "when" statement is only used with "augment", "must" is used
      elsewhere.

   o  Additional "must" statements were added.

   o  The "route-content" grouping for IPv4 and IPv6 unicast now
      includes the material from the "ietf-routing" version via "uses
      rt:route-content".

   o  Explanation of symbols in the tree representation of data model
      hierarchy.

E.16.  Changes Between Versions -00 and -01

   o  AFN/SAFI-independent stuff was moved to the "ietf-routing" module.

   o  Typedefs for AFN and SAFI were placed in a separate "iana-afn-
      safi" module.




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   o  Names of some data nodes were changed, in particular "routing-
      process" is now "router".

   o  The restriction of a single AFN/SAFI per router was lifted.

   o  RPC operation "delete-route" was removed.

   o  Illegal XPath references from "get-route" to the datastore were
      fixed.

   o  Section "Security Considerations" was written.

Author's Address

   Ladislav Lhotka
   CZ.NIC

   Email: lhotka@nic.cz

































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