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+Internet Engineering Task Force (IETF)                         A. Lindem
+Request for Comments: 9403                       LabN Consulting, L.L.C.
+Category: Standards Track                                          Y. Qu
+ISSN: 2070-1721                                   Futurewei Technologies
+                                                           November 2023
+
+
+                  A YANG Data Model for RIB Extensions
+
+Abstract
+
+   A Routing Information Base (RIB) is a list of routes and their
+   corresponding administrative data and operational state.
+
+   RFC 8349 defines the basic building blocks for the RIB data model,
+   and this model augments it to support multiple next hops (aka paths)
+   for each route as well as additional attributes.
+
+Status of This Memo
+
+   This is an Internet Standards Track document.
+
+   This document is a product of the Internet Engineering Task Force
+   (IETF).  It represents the consensus of the IETF community.  It has
+   received public review and has been approved for publication by the
+   Internet Engineering Steering Group (IESG).  Further information on
+   Internet Standards is available in Section 2 of RFC 7841.
+
+   Information about the current status of this document, any errata,
+   and how to provide feedback on it may be obtained at
+   https://www.rfc-editor.org/info/rfc9403.
+
+Copyright Notice
+
+   Copyright (c) 2023 IETF Trust and the persons identified as the
+   document authors.  All rights reserved.
+
+   This document is subject to BCP 78 and the IETF Trust's Legal
+   Provisions Relating to IETF Documents
+   (https://trustee.ietf.org/license-info) in effect on the date of
+   publication of this document.  Please review these documents
+   carefully, as they describe your rights and restrictions with respect
+   to this document.  Code Components extracted from this document must
+   include Revised BSD License text as described in Section 4.e of the
+   Trust Legal Provisions and are provided without warranty as described
+   in the Revised BSD License.
+
+Table of Contents
+
+   1.  Introduction
+   2.  Terminology and Notation
+     2.1.  Tree Diagrams
+     2.2.  Prefixes in Data Node Names
+   3.  Design of the Model
+     3.1.  Tags and Preferences
+     3.2.  Repair Path
+   4.  RIB Model Tree
+   5.  RIB Extension YANG Module
+   6.  Security Considerations
+   7.  IANA Considerations
+   8.  References
+     8.1.  Normative References
+     8.2.  Informative References
+   Appendix A.  Combined Tree Diagram
+   Appendix B.  ietf-rib-extension.yang example
+   Acknowledgments
+   Authors' Addresses
+
+1.  Introduction
+
+   This document defines a YANG data model [RFC7950] that extends the
+   RIB data model defined in the ietf-routing YANG module [RFC8349] with
+   more route attributes.
+
+   A RIB is a collection of routes with attributes controlled and
+   manipulated by control plane protocols.  Each RIB contains only
+   routes of one address family [RFC8349].  Within a protocol, routes
+   are selected based on the metrics in use by that protocol, and the
+   protocol installs the routes to the RIB.  The RIB selects the
+   preferred or active route by comparing the route preference (aka
+   administrative distance) of the candidate routes installed by
+   different protocols.
+
+   The module defined in this document extends the RIB to support more
+   route attributes, such as multiple next hops, route metrics, and
+   administrative tags.
+
+   The YANG modules defined and discussed in this document conform to
+   the Network Management Datastore Architecture (NMDA) [RFC8342].
+
+2.  Terminology and Notation
+
+   The following terms are defined in [RFC8342]:
+
+   *  configuration
+
+   *  system state
+
+   *  operational state
+
+   The following terms are defined in [RFC7950]:
+
+   *  action
+
+   *  augment
+
+   *  container
+
+   *  container with presence
+
+   *  data model
+
+   *  data node
+
+   *  leaf
+
+   *  list
+
+   *  mandatory node
+
+   *  module
+
+   *  schema tree
+
+   The following term is defined in [RFC8349], Section 5.2:
+
+   *  RIB
+
+2.1.  Tree Diagrams
+
+   Tree diagrams used in this document follow the notation defined in
+   [RFC8340].
+
+2.2.  Prefixes in Data Node Names
+
+   In this document, names of data nodes, actions, 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.
+
+            +========+===========================+===========+
+            | Prefix | YANG Module               | Reference |
+            +========+===========================+===========+
+            | if     | ietf-interfaces           | [RFC8343] |
+            +--------+---------------------------+-----------+
+            | rt     | ietf-routing              | [RFC8349] |
+            +--------+---------------------------+-----------+
+            | v4ur   | ietf-ipv4-unicast-routing | [RFC8349] |
+            +--------+---------------------------+-----------+
+            | v6ur   | ietf-ipv6-unicast-routing | [RFC8349] |
+            +--------+---------------------------+-----------+
+            | inet   | ietf-inet-types           | [RFC6991] |
+            +--------+---------------------------+-----------+
+            | ospf   | ietf-ospf                 | [RFC9129] |
+            +--------+---------------------------+-----------+
+            | isis   | ietf-isis                 | [RFC9130] |
+            +--------+---------------------------+-----------+
+
+             Table 1: Prefixes and Corresponding YANG Modules
+
+3.  Design of the Model
+
+   The YANG module defined in this document augments the ietf-routing,
+   ietf-ipv4-unicast-routing, and ietf-ipv6-unicast-routing YANG modules
+   defined in [RFC8349], which provide a basis for routing system data
+   model development.  Together with the ietf-routing YANG module and
+   other YANG modules defined in [RFC8349], a generic RIB YANG data
+   model is defined herein to implement and monitor a RIB.
+
+   The modules in [RFC8349] also define the basic configuration and
+   operational state for both IPv4 and IPv6 static routes.  This
+   document provides augmentations for static routes to support multiple
+   next hops and more next-hop attributes.
+
+3.1.  Tags and Preferences
+
+   Individual route tags are supported at both the route and next-hop
+   level.  A preference per next hop is also supported for selection of
+   the most preferred reachable static route.
+
+   The following tree snapshot shows tag and preference entries that
+   augment static IPv4 unicast route and IPv6 unicast route next hops.
+
+     augment /rt:routing/rt:control-plane-protocols
+             /rt:control-plane-protocol/rt:static-routes/v4ur:ipv4
+             /v4ur:route/v4ur:next-hop/v4ur:next-hop-options
+             /v4ur:simple-next-hop:
+       +--rw preference?   uint32
+       +--rw tag?          uint32
+     augment /rt:routing/rt:control-plane-protocols
+             /rt:control-plane-protocol/rt:static-routes/v4ur:ipv4
+             /v4ur:route/v4ur:next-hop/v4ur:next-hop-options
+             /v4ur:next-hop-list/v4ur:next-hop-list/v4ur:next-hop:
+       +--rw preference?   uint32
+       +--rw tag?          uint32
+     augment /rt:routing/rt:control-plane-protocols
+             /rt:control-plane-protocol/rt:static-routes/v6ur:ipv6
+             /v6ur:route/v6ur:next-hop/v6ur:next-hop-options
+             /v6ur:simple-next-hop:
+       +--rw preference?   uint32
+       +--rw tag?          uint32
+     augment /rt:routing/rt:control-plane-protocols
+             /rt:control-plane-protocol/rt:static-routes/v6ur:ipv6
+             /v6ur:route/v6ur:next-hop/v6ur:next-hop-options
+             /v6ur:next-hop-list/v6ur:next-hop-list/v6ur:next-hop:
+       +--rw preference?   uint32
+       +--rw tag?          uint32
+     augment /rt:routing/rt:ribs/rt:rib/rt:routes/rt:route:
+       +--ro metric?            uint32
+       +--ro tag*               uint32
+       +--ro application-tag?   uint32
+
+3.2.  Repair Path
+
+   The IP Fast Reroute (IPFRR) calculation by routing protocol
+   precomputes repair paths [RFC5714], and the repair paths are
+   installed in the RIB.
+
+   Each route next hop in the RIB is augmented with a repair path and is
+   shown in the following tree snapshot.
+
+     augment /rt:routing/rt:ribs/rt:rib/rt:routes/rt:route
+             /rt:next-hop/rt:next-hop-options/rt:simple-next-hop:
+       +--ro repair-path
+          +--ro outgoing-interface?   if:interface-state-ref
+          +--ro next-hop-address?     inet:ip-address-no-zone
+          +--ro metric?               uint32
+     augment /rt:routing/rt:ribs/rt:rib/rt:routes/rt:route
+             /rt:next-hop/rt:next-hop-options/rt:next-hop-list
+             /rt:next-hop-list/rt:next-hop:
+       +--ro repair-path
+          +--ro outgoing-interface?   if:interface-state-ref
+          +--ro next-hop-address?     inet:ip-address-no-zone
+          +--ro metric?               uint32
+
+4.  RIB Model Tree
+
+   The ietf-routing.yang tree with the augmentations herein is included
+   in Appendix A.  The meanings of the symbols can be found in
+   [RFC8340].
+
+5.  RIB Extension YANG Module
+
+   This YANG module references [RFC6991], [RFC8343], [RFC8349],
+   [RFC9129], [RFC9130], and [RFC5714].
+
+   <CODE BEGINS> file "ietf-rib-extension@2023-11-20.yang"
+   module ietf-rib-extension {
+     yang-version 1.1;
+     namespace "urn:ietf:params:xml:ns:yang:ietf-rib-extension";
+     prefix rib-ext;
+
+     import ietf-inet-types {
+       prefix inet;
+       reference
+         "RFC 6991: Common YANG Data Types";
+     }
+     import ietf-interfaces {
+       prefix if;
+       reference
+         "RFC 8343: A YANG Data Model for Interface
+                    Management";
+     }
+     import ietf-routing {
+       prefix rt;
+       reference
+         "RFC 8349: A YANG Data Model for Routing
+                    Management (NMDA Version)";
+     }
+     import ietf-ipv4-unicast-routing {
+       prefix v4ur;
+       reference
+         "RFC 8349: A YANG Data Model for Routing
+                    Management (NMDA Version)";
+     }
+     import ietf-ipv6-unicast-routing {
+       prefix v6ur;
+       reference
+         "RFC 8349: A YANG Data Model for Routing
+                    Management (NMDA Version)";
+     }
+
+     import ietf-ospf {
+       prefix ospf;
+       reference "RFC 9129: YANG Data Model for the OSPF Protocol";
+     }
+
+     import ietf-isis {
+       prefix isis;
+       reference "RFC 9130: YANG Data Model for the IS-IS Protocol";
+     }
+
+     organization
+       "IETF RTGWG (Routing Area Working Group)";
+     contact
+       "WG Web:   <https://datatracker.ietf.org/wg/rtgwg/>
+        WG List:  <mailto:rtgwg@ietf.org>
+
+        Author:   Acee Lindem
+                  <mailto:acee.ietf@gmail.com>
+        Author:   Yingzhen Qu
+                  <mailto:yingzhen.qu@futurewei.com>";
+     description
+       "This YANG module extends the RIB defined in the ietf-routing
+        YANG module with additional route attributes.
+
+        This YANG module conforms to the Network Management
+        Datastore Architecture (NMDA) as described in RFC 8342.
+
+        Copyright (c) 2023 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 Revised BSD License set
+        forth in Section 4.c of the IETF Trust's Legal Provisions
+        Relating to IETF Documents
+        (https://trustee.ietf.org/license-info).
+
+        This version of this YANG module is part of RFC 9403; see the
+        RFC itself for full legal notices.";
+
+     revision 2023-11-20 {
+       description
+         "Initial version.";
+       reference
+         "RFC 9403: A YANG Data Model for RIB Extensions";
+     }
+
+     /* Groupings */
+
+     grouping rib-statistics {
+       description
+         "Statistics grouping used for RIB augmentation.";
+       container statistics {
+         config false;
+         description
+           "Container for RIB statistics.";
+         leaf total-routes {
+           type uint32;
+           description
+             "Total number of routes in the RIB.";
+         }
+         leaf total-active-routes {
+           type uint32;
+           description
+             "Total number of active routes in the RIB.  An active
+              route is the route that is preferred over other routes
+              to the same destination prefix.";
+         }
+         leaf total-route-memory {
+           type uint64;
+           units "bytes";
+           description
+             "Total memory for all routes in the RIB.";
+         }
+         list protocol-statistics {
+           description
+             "RIB statistics for routing protocols installing
+              routes in the RIB.";
+           leaf protocol {
+             type identityref {
+               base rt:routing-protocol;
+             }
+             description
+               "Routing protocol installing routes in the RIB.";
+           }
+           leaf routes {
+             type uint32;
+             description
+               "Total number of routes in the RIB for the routing
+                protocol identified by the 'protocol' entry.";
+           }
+           leaf active-routes {
+             type uint32;
+             description
+               "Total number of active routes in the RIB for the
+                routing protocol identified by the 'protocol' entry.
+                An active route is preferred over other routes to the
+                same destination prefix.";
+           }
+           leaf route-memory {
+             type uint64;
+             units "bytes";
+             description
+               "Total memory for all routes in the RIB for the
+                routing protocol identified by the 'protocol'
+                entry.";
+           }
+         }
+       }
+     }
+
+     grouping repair-path {
+       description
+         "Grouping for the IP Fast Reroute (IPFRR) repair path.";
+       container repair-path {
+         description
+           "IPFRR next-hop repair path.";
+         leaf outgoing-interface {
+           type if:interface-state-ref;
+           description
+             "Name of the outgoing interface.";
+         }
+         leaf next-hop-address {
+           type inet:ip-address-no-zone;
+           description
+             "IP address of the next hop.";
+         }
+         leaf metric {
+           type uint32;
+           description
+             "The metric for the repair path.  While the reroute
+              repair is local and the metric is not advertised
+              externally, the metric for the repair path is useful
+              for troubleshooting purposes.";
+         }
+         reference
+           "RFC 5714: IP Fast Reroute Framework";
+       }
+     }
+
+     augment "/rt:routing/rt:control-plane-protocols/"
+           + "rt:control-plane-protocol/rt:static-routes/v4ur:ipv4/"
+           + "v4ur:route/v4ur:next-hop/v4ur:next-hop-options/"
+           + "v4ur:simple-next-hop" {
+       description
+         "Augment 'simple-next-hop' case in IPv4 unicast route.";
+       leaf preference {
+         type uint32;
+         default "1";
+         description
+           "The preference is used to select among multiple static
+            routes.  Routes with a lower next-hop preference value
+            are preferred, and equal-preference routes result in
+            Equal-Cost Multipath (ECMP) static routes.";
+       }
+       leaf tag {
+         type uint32;
+         default "0";
+         description
+           "The tag is a 32-bit opaque value associated with the
+            route that can be used for policy decisions such as
+            advertisement and filtering of the route.";
+       }
+     }
+
+     augment "/rt:routing/rt:control-plane-protocols/"
+           + "rt:control-plane-protocol/rt:static-routes/v4ur:ipv4/"
+           + "v4ur:route/v4ur:next-hop/v4ur:next-hop-options/"
+           + "v4ur:next-hop-list/v4ur:next-hop-list/v4ur:next-hop" {
+       description
+         "Augment static route configuration 'next-hop-list'.";
+       leaf preference {
+         type uint32;
+         default "1";
+         description
+           "The preference is used to select among multiple static
+            routes.  Routes with a lower next-hop preference value
+            are preferred, and equal-preference routes result in
+            ECMP static routes.";
+       }
+       leaf tag {
+         type uint32;
+         default "0";
+         description
+           "The tag is a 32-bit opaque value associated with the
+            route that can be used for policy decisions such as
+            advertisement and filtering of the route.";
+       }
+     }
+
+     augment "/rt:routing/rt:control-plane-protocols/"
+           + "rt:control-plane-protocol/rt:static-routes/v6ur:ipv6/"
+           + "v6ur:route/v6ur:next-hop/v6ur:next-hop-options/"
+           + "v6ur:simple-next-hop" {
+       description
+         "Augment 'simple-next-hop' case in IPv6 unicast route.";
+       leaf preference {
+         type uint32;
+         default "1";
+         description
+           "The preference is used to select among multiple static
+            routes.  Routes with a lower next-hop preference value
+            are preferred, and equal-preference routes result in
+            ECMP static routes.";
+       }
+       leaf tag {
+         type uint32;
+         default "0";
+         description
+           "The tag is a 32-bit opaque value associated with the
+            route that can be used for policy decisions such as
+            advertisement and filtering of the route.";
+       }
+     }
+
+     augment "/rt:routing/rt:control-plane-protocols/"
+           + "rt:control-plane-protocol/rt:static-routes/v6ur:ipv6/"
+           + "v6ur:route/v6ur:next-hop/v6ur:next-hop-options/"
+           + "v6ur:next-hop-list/v6ur:next-hop-list/v6ur:next-hop" {
+       description
+         "Augment static route configuration 'next-hop-list'.";
+       leaf preference {
+         type uint32;
+         default "1";
+         description
+           "The preference is used to select among multiple static
+            routes.  Routes with a lower next-hop preference value
+            are preferred, and equal-preference routes result in
+            ECMP static routes.";
+       }
+       leaf tag {
+         type uint32;
+         default "0";
+         description
+           "The tag is a 32-bit opaque value associated with the
+            route that can be used for policy decisions such as
+            advertisement and filtering of the route.";
+       }
+     }
+
+     augment "/rt:routing/rt:ribs/rt:rib" {
+       description
+         "Augment a RIB with statistics.";
+       uses rib-statistics;
+     }
+
+     augment "/rt:routing/rt:ribs/rt:rib/"
+           + "rt:routes/rt:route" {
+       description
+         "Augment a route in the RIB with common attributes.";
+       leaf metric {
+         when "not(derived-from("
+           + "../rt:source-protocol, 'ospf:ospf')) "
+           + "and not(derived-from( "
+           + "../rt:source-protocol, 'isis:isis'))" {
+           description
+             "This augmentation is only valid for routes that don't
+              have OSPF or IS-IS as the source protocol.  The YANG
+              data models for OSPF and IS-IS already include a
+              'metric' augmentation for routes.";
+         }
+         type uint32;
+         description
+           "The metric is a numeric value indicating the cost
+            of the route from the perspective of the routing
+            protocol installing the route.  In general, routes with
+            a lower metric installed by the same routing protocol
+            are lower cost to reach and are preferable to routes
+            with a higher metric.  However, metrics from different
+            routing protocols are not comparable.";
+       }
+       leaf-list tag {
+         when "not(derived-from("
+           + "../rt:source-protocol, 'ospf:ospf')) "
+           + "and not(derived-from( "
+           + "../rt:source-protocol, 'isis:isis'))" {
+           description
+             "This augmentation is only valid for routes that don't
+              have OSPF or IS-IS as the source protocol.  The YANG
+              data models for OSPF and IS-IS already include a 'tag'
+              augmentation for routes.";
+         }
+         type uint32;
+         description
+           "A tag is a 32-bit opaque value associated with the
+            route that can be used for policy decisions such as
+            advertisement and filtering of the route.";
+       }
+       leaf application-tag {
+         type uint32;
+         description
+           "The application-specific tag is an additional tag that
+            can be used by applications that require semantics and/or
+            policy different from that of the tag.  For example,
+            the tag is usually automatically advertised in OSPF
+            AS-External Link State Advertisements (LSAs) while this
+            application-specific tag is not advertised implicitly.";
+       }
+     }
+
+     augment "/rt:routing/rt:ribs/rt:rib/"
+           + "rt:routes/rt:route/rt:next-hop/rt:next-hop-options/"
+           + "rt:simple-next-hop" {
+       description
+         "Augment 'simple-next-hop' with 'repair-path'.";
+       uses repair-path;
+     }
+
+     augment "/rt:routing/rt:ribs/rt:rib/"
+           + "rt:routes/rt:route/rt:next-hop/rt:next-hop-options/"
+           + "rt:next-hop-list/rt:next-hop-list/rt:next-hop" {
+       description
+         "Augment the next hop with a repair path.";
+       uses repair-path;
+     }
+   }
+   <CODE ENDS>
+
+6.  Security Considerations
+
+   The YANG module specified in this document defines a schema for data
+   that is designed to be accessed via network management protocols such
+   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
+   is the secure transport layer, and the mandatory-to-implement secure
+   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
+   is HTTPS, and the mandatory-to-implement secure transport is TLS
+   [RFC8446].
+
+   The Network Configuration Access Control Model (NACM) [RFC8341]
+   provides the means to restrict access for particular NETCONF or
+   RESTCONF users to a preconfigured subset of all available NETCONF or
+   RESTCONF protocol operations and content.
+
+   There are a number of data nodes defined in the ietf-rib-
+   extension.yang module that are writable/creatable/deletable (i.e.,
+   config true, which is the default).  These data nodes may be
+   considered sensitive or vulnerable in some network environments.
+   Write operations (e.g., edit-config) to these data nodes without
+   proper protection can have a negative effect on network operations.
+   These are the subtrees and data nodes and their sensitivity/
+   vulnerability:
+
+   *  /v4ur:next-hop-options/v4ur:simple-next-hop/rib-ext:preference
+
+   *  /v4ur:next-hop-options/v4ur:simple-next-hop/rib-ext:tag
+
+   *  /v4ur:next-hop-options/v4ur:next-hop-list/v4ur:next-hop-list
+      /v4ur:next-hop/rib-ext:preference
+
+   *  /v4ur:next-hop-options/v4ur:next-hop-list/v4ur:next-hop-list
+      /v4ur:next-hop/rib-ext:tag
+
+   *  /v6ur:next-hop-options/v6ur:simple-next-hop/rib-ext:preference
+
+   *  /v6ur:next-hop-options/v6ur:simple-next-hop/rib-ext:tag
+
+   *  /v6ur:next-hop-options/v6ur:next-hop-list/v6ur:next-hop-list
+      /v6ur:next-hop/rib-ext:preference
+
+   *  /v6ur:next-hop-options/v6ur:next-hop-list/v6ur:next-hop-list
+      /v6ur:next-hop/rib-ext:tag
+
+      For these augmentations to ietf-routing.yang, the ability to
+      delete, add, and modify IPv4 and IPv6 static route preferences and
+      tags would allow traffic to be misrouted.
+
+   Some of the readable data nodes in the ietf-rib-extension.yang module
+   may be considered sensitive or vulnerable in some network
+   environments.  It is thus important to control read access (e.g., via
+   get, get-config, or notification) to these data nodes.  These are the
+   subtrees and data nodes and their sensitivity/vulnerability:
+
+   *  /rt:routing/rt:ribs/rt:rib/rib-ext:statistics
+
+   *  /rt:routing/rt:ribs/rt:rib/rt:routes/rt:route/rib-ext:metric
+
+   *  /rt:routing/rt:ribs/rt:rib/rt:routes/rt:route/rib-ext:tag
+
+   *  /rt:routing/rt:ribs/rt:rib/rt:routes/rt:route/rib-ext:application-
+      tag
+
+   *  /rt:route/rt:next-hop/rt:next-hop-options/rt:simple-next-hop/rib-
+      ext:repair-path
+
+   *  /rt:routes/rt:route/rt:next-hop/rt:next-hop-options/rt:next-hop-
+      list/rt:next-hop-list/rt:next-hop/rib-ext:repair-path
+
+      Exposing the RIB will expose the routing topology of the network.
+      This may be undesirable due to the fact that such exposure may
+      facilitate other attacks.  Additionally, network operators may
+      consider their topologies to be sensitive confidential data.
+
+   All the security considerations for writable and readable data nodes
+   defined in [RFC8349] apply to the augmentations described herein.
+
+7.  IANA Considerations
+
+   This document registers the following URI in the "IETF XML Registry"
+   [RFC3688].
+
+   URI:  urn:ietf:params:xml:ns:yang:ietf-rib-extension
+   Registrant Contact:  The IESG.
+   XML:  N/A; the requested URI is an XML namespace.
+
+   IANA has registered the following YANG module in the "YANG Module
+   Names" registry [RFC6020].
+
+   Name:  ietf-rib-extension
+   Namespace:  urn:ietf:params:xml:ns:yang:ietf-rib-extension
+   Prefix:  rib-ext
+   Reference:  RFC 9403
+
+8.  References
+
+8.1.  Normative References
+
+   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
+              DOI 10.17487/RFC3688, January 2004,
+              <https://www.rfc-editor.org/info/rfc3688>.
+
+   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
+              the Network Configuration Protocol (NETCONF)", RFC 6020,
+              DOI 10.17487/RFC6020, October 2010,
+              <https://www.rfc-editor.org/info/rfc6020>.
+
+   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
+              and A. Bierman, Ed., "Network Configuration Protocol
+              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
+              <https://www.rfc-editor.org/info/rfc6241>.
+
+   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
+              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
+              <https://www.rfc-editor.org/info/rfc6242>.
+
+   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
+              RFC 6991, DOI 10.17487/RFC6991, July 2013,
+              <https://www.rfc-editor.org/info/rfc6991>.
+
+   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
+              RFC 7950, DOI 10.17487/RFC7950, August 2016,
+              <https://www.rfc-editor.org/info/rfc7950>.
+
+   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
+              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
+              <https://www.rfc-editor.org/info/rfc8040>.
+
+   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
+              Access Control Model", STD 91, RFC 8341,
+              DOI 10.17487/RFC8341, March 2018,
+              <https://www.rfc-editor.org/info/rfc8341>.
+
+   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
+              and R. Wilton, "Network Management Datastore Architecture
+              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
+              <https://www.rfc-editor.org/info/rfc8342>.
+
+   [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
+              Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
+              <https://www.rfc-editor.org/info/rfc8343>.
+
+   [RFC8349]  Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
+              Routing Management (NMDA Version)", RFC 8349,
+              DOI 10.17487/RFC8349, March 2018,
+              <https://www.rfc-editor.org/info/rfc8349>.
+
+   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
+              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
+              <https://www.rfc-editor.org/info/rfc8446>.
+
+   [RFC9129]  Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem,
+              "YANG Data Model for the OSPF Protocol", RFC 9129,
+              DOI 10.17487/RFC9129, October 2022,
+              <https://www.rfc-editor.org/info/rfc9129>.
+
+   [RFC9130]  Litkowski, S., Ed., Yeung, D., Lindem, A., Zhang, J., and
+              L. Lhotka, "YANG Data Model for the IS-IS Protocol",
+              RFC 9130, DOI 10.17487/RFC9130, October 2022,
+              <https://www.rfc-editor.org/info/rfc9130>.
+
+   [W3C.REC-xml-20081126]
+              Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
+              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
+              Edition)", World Wide Web Consortium Recommendation REC-
+              xml-20081126, November 2008,
+              <https://www.w3.org/TR/2008/REC-xml-20081126>.
+
+8.2.  Informative References
+
+   [RFC5714]  Shand, M. and S. Bryant, "IP Fast Reroute Framework",
+              RFC 5714, DOI 10.17487/RFC5714, January 2010,
+              <https://www.rfc-editor.org/info/rfc5714>.
+
+   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
+              RFC 7951, DOI 10.17487/RFC7951, August 2016,
+              <https://www.rfc-editor.org/info/rfc7951>.
+
+   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
+              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
+              <https://www.rfc-editor.org/info/rfc8340>.
+
+   [RFC8792]  Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
+              "Handling Long Lines in Content of Internet-Drafts and
+              RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
+              <https://www.rfc-editor.org/info/rfc8792>.
+
+Appendix A.  Combined Tree Diagram
+
+   This appendix provides the combined ietf-routing.yang, ietf-ipv4-
+   unicast-routing.yang, ietf-ipv6-unicast-routing.yang, and ietf-rib-
+   extension.yang tree diagram.
+
+   module: ietf-routing
+     +--rw routing
+     +--rw router-id?                 yang:dotted-quad {router-id}?
+     +--ro interfaces
+     |  +--ro interface*   if:interface-ref
+     +--rw control-plane-protocols
+     |  +--rw control-plane-protocol* [type name]
+     |     +--rw type             identityref
+     |     +--rw name             string
+     |     +--rw description?     string
+     |     +--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 (v4ur:next-hop-options)
+     |        |           +--:(v4ur:simple-next-hop)
+     |        |           |  +--rw v4ur:outgoing-interface?
+     |        |           |  |   if:interface-ref
+     |        |           |  +--rw v4ur:next-hop-address?
+     |        |           |  |   inet:ipv4-address
+     |        |           |  +--rw rib-ext:preference?      uint32
+     |        |           |  +--rw rib-ext:tag?             uint32
+     |        |           +--:(v4ur:special-next-hop)
+     |        |           |  +--rw v4ur:special-next-hop?   enumeration
+     |        |           +--:(v4ur:next-hop-list)
+     |        |              +--rw v4ur:next-hop-list
+     |        |                 +--rw v4ur:next-hop* [index]
+     |        |                    +--rw v4ur:index            string
+     |        |                    +--rw v4ur:outgoing-interface?
+     |        |                    |   if:interface-ref
+     |        |                    +--rw v4ur:next-hop-address?
+     |        |                    |   inet:ipv4-address
+     |        |                    +--rw rib-ext:preference?   uint32
+     |        |                    +--rw rib-ext:tag?          uint32
+     |        +--rw v6ur:ipv6
+     |           +--rw v6ur:route* [destination-prefix]
+     |              +--rw v6ur:destination-prefix    inet:ipv6-prefix
+     |              +--rw v6ur:description?          string
+     |              +--rw v6ur:next-hop
+     |                 +--rw (v6ur:next-hop-options)
+     |                    +--:(v6ur:simple-next-hop)
+     |                    |  +--rw v6ur:outgoing-interface?
+     |                    |  |   if:interface-ref
+     |                    |  +--rw v6ur:next-hop-address?
+     |                    |  |   inet:ipv6-address
+     |                    |  +--rw rib-ext:preference?      uint32
+     |                    |  +--rw rib-ext:tag?             uint32
+     |                    +--:(v6ur:special-next-hop)
+     |                    |  +--rw v6ur:special-next-hop?   enumeration
+     |                    +--:(v6ur:next-hop-list)
+     |                       +--rw v6ur:next-hop-list
+     |                          +--rw v6ur:next-hop* [index]
+     |                             +--rw v6ur:index              string
+     |                             +--rw v6ur:outgoing-interface?
+     |                             |   if:interface-ref
+     |                             +--rw v6ur:next-hop-address?
+     |                             |   inet:ipv6-address
+     |                             +--rw rib-ext:preference?     uint32
+     |                             +--rw rib-ext:tag?            uint32
+     +--rw ribs
+        +--rw rib* [name]
+           +--rw name                          string
+           +--rw address-family                identityref
+           +--ro default-rib?                  boolean {multiple-ribs}?
+           +--ro routes
+           |  +--ro route* []
+           |     +--ro route-preference?       route-preference
+           |     +--ro next-hop
+           |     |  +--ro (next-hop-options)
+           |     |     +--:(simple-next-hop)
+           |     |     |  +--ro outgoing-interface?
+           |     |     |  |   if:interface-ref
+           |     |     |  +--ro v4ur:next-hop-address?
+           |     |     |  |   inet:ipv4-address
+           |     |     |  +--ro v6ur:next-hop-address?
+           |     |     |  |   inet:ipv6-address
+           |     |     |  +--ro rib-ext:repair-path
+           |     |     |     +--ro rib-ext:outgoing-interface?
+           |     |     |     |   if:interface-state-ref
+           |     |     |     +--ro rib-ext:next-hop-address?
+           |     |     |     |   inet:ip-address-no-zone
+           |     |     |     +--ro rib-ext:metric?               uint32
+           |     |     +--:(special-next-hop)
+           |     |     |  +--ro special-next-hop?        enumeration
+           |     |     +--:(next-hop-list)
+           |     |        +--ro next-hop-list
+           |     |           +--ro next-hop* []
+           |     |              +--ro outgoing-interface?
+           |     |              |   if:interface-ref
+           |     |              +--ro v4ur:address?
+           |     |              |   inet:ipv4-address
+           |     |              +--ro v6ur:address?
+           |     |              |   inet:ipv6-address
+           |     |              +--ro rib-ext:repair-path
+           |     |                 +--ro rib-ext:outgoing-interface?
+           |     |                 |   if:interface-state-ref
+           |     |                 +--ro rib-ext:next-hop-address?
+           |     |                 |   inet:ip-address-no-zone
+           |     |                 +--ro rib-ext:metric?         uint32
+           |     +--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 rib-ext:metric?            uint32
+           |     +--ro rib-ext:tag*               uint32
+           |     +--ro rib-ext:application-tag?   uint32
+           +---x active-route
+           |  +---w input
+           |  |  +---w v4ur:destination-address?   inet:ipv4-address
+           |  |  +---w v6ur:destination-address?   inet:ipv6-address
+           |  +--ro output
+           |     +--ro route
+           |        +--ro next-hop
+           |        |  +--ro (next-hop-options)
+           |        |     +--:(simple-next-hop)
+           |        |     |  +--ro outgoing-interface?
+           |        |     |  |   if:interface-ref
+           |        |     |  +--ro v4ur:next-hop-address?
+           |        |     |  |   inet:ipv4-address
+           |        |     |  +--ro v6ur:next-hop-address?
+           |        |     |  |   inet:ipv6-address
+           |        |     +--:(special-next-hop)
+           |        |     |  +--ro special-next-hop?        enumeration
+           |        |     +--:(next-hop-list)
+           |        |        +--ro next-hop-list
+           |        |           +--ro next-hop* []
+           |        |              +--ro outgoing-interface?
+           |        |              |   if:interface-ref
+           |        |              +--ro v4ur:next-hop-address?
+           |        |              |   inet:ipv4-address
+           |        |              +--ro v6ur:next-hop-address?
+           |        |              |   inet:ipv6-address
+           |        +--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
+           +--rw description?                        string
+           +--ro rib-ext:statistics
+              +--ro rib-ext:total-routes?              uint32
+              +--ro rib-ext:total-active-routes?       uint32
+              +--ro rib-ext:total-route-memory?        uint64
+              +--ro rib-ext:protocol-statistics* []
+                 +--ro rib-ext:protocol?             identityref
+                 +--ro rib-ext:routes?    uint32
+                 +--ro rib-ext:active-routes?   uint32
+                 +--ro rib-ext:route-memory?    uint64
+
+Appendix B.  ietf-rib-extension.yang example
+
+   The following is an XML example [W3C.REC-xml-20081126] using the RIB
+   extension module and RFC 8349.
+
+      |  Note: '\' line wrapping per [RFC8792].
+
+   <routing xmlns="urn:ietf:params:xml:ns:yang:ietf-routing">
+     <control-plane-protocols>
+       <control-plane-protocol>
+         <type>static</type>
+         <name>static-routing-protocol</name>
+         <static-routes>
+           <ipv4 xmlns="urn:ietf:params:xml:ns:yang:\
+             ietf-ipv4-unicast-routing">
+             <route>
+               <destination-prefix>0.0.0.0/0</destination-prefix>
+               <next-hop>
+                 <next-hop-address>192.0.2.2</next-hop-address>
+                 <preference xmlns="urn:ietf:params:xml:ns:yang:\
+                   ietf-rib-extension">30</preference>
+                 <tag xmlns="urn:ietf:params:xml:ns:yang:\
+                   ietf-rib-extension">99</tag>
+               </next-hop>
+             </route>
+           </ipv4>
+           <ipv6 xmlns="urn:ietf:params:xml:ns:yang:\
+             ietf-ipv6-unicast-routing">
+             <route>
+               <destination-prefix>::/0</destination-prefix>
+               <next-hop>
+                <next-hop-address>2001:db8:aaaa::1111</next-hop-address>
+                <preference xmlns="urn:ietf:params:xml:ns:yang:\
+                  ietf-rib-extension">30</preference>
+                <tag xmlns="urn:ietf:params:xml:ns:yang:\
+                  ietf-rib-extension">66</tag>
+               </next-hop>
+             </route>
+           </ipv6>
+         </static-routes>
+       </control-plane-protocol>
+     </control-plane-protocols>
+     <ribs>
+       <rib>
+         <name>ipv4-primary</name>
+         <address-family xmlns:v4ur="urn:ietf:params:xml:ns:yang:\
+           ietf-ipv4-unicast-routing">v4ur:ipv4-unicast</address-family>
+         <default-rib>true</default-rib>
+         <routes>
+           <route>
+             <destination-prefix xmlns="urn:ietf:params:xml:ns:yang:\
+               ietf-ipv4-unicast-routing">0.0.0.0/0</destination-prefix>
+             <next-hop>
+               <next-hop-address xmlns="urn:ietf:params:xml:ns:yang:\
+                 ietf-ipv4-unicast-routing">192.0.2.2</next-hop-address>
+             </next-hop>
+             <route-preference>5</route-preference>
+             <source-protocol>static</source-protocol>
+             <last-updated>2015-10-24T18:02:45+02:00</last-updated>
+           </route>
+           <route>
+             <destination-prefix xmlns="urn:ietf:params:xml:ns:yang:\
+               ietf-ipv4-unicast-routing">198.51.100.0/24\
+             </destination-prefix>
+             <next-hop>
+               <next-hop-address xmlns="urn:ietf:params:xml:ns:yang:\
+                 ietf-ipv4-unicast-routing">192.0.2.2</next-hop-address>
+               <repair-path xmlns="urn:ietf:params:xml:ns:yang:\
+                 ietf-rib-extension">
+                 <next-hop-address>203.0.113.1</next-hop-address>
+                 <metric>200</metric>
+               </repair-path>
+             </next-hop>
+             <route-preference>120</route-preference>
+             <source-protocol xmlns:rip="urn:ietf:params:xml:ns:yang:\
+               ietf-rip">rip:rip</source-protocol>
+             <last-updated>2015-10-24T18:02:45+02:00</last-updated>
+           </route>
+         </routes>
+       </rib>
+       <rib>
+         <name>ipv6-primary</name>
+         <address-family xmlns:v6ur="urn:ietf:params:xml:ns:yang:\
+           ietf-ipv6-unicast-routing">v6ur:ipv6-unicast</address-family>
+         <default-rib>true</default-rib>
+         <routes>
+           <route>
+             <destination-prefix xmlns="urn:ietf:params:xml:ns:yang:\
+               ietf-ipv6-unicast-routing">0::/0</destination-prefix>
+             <next-hop>
+               <next-hop-address xmlns="urn:ietf:params:xml:ns:yang:\
+                 ietf-ipv6-unicast-routing">2001:db8:aaaa::1111\
+               </next-hop-address>
+             </next-hop>
+             <route-preference>5</route-preference>
+             <source-protocol>static</source-protocol>
+             <last-updated>2015-10-24T18:02:45+02:00</last-updated>
+           </route>
+           <route>
+             <destination-prefix xmlns="urn:ietf:params:xml:ns:yang:\
+               ietf-ipv6-unicast-routing">2001:db8:bbbb::/64\
+             </destination-prefix>
+             <next-hop>
+               <next-hop-address xmlns="urn:ietf:params:xml:ns:yang:\
+                 ietf-ipv6-unicast-routing">2001:db8:aaaa::1111\
+               </next-hop-address>
+               <repair-path xmlns="urn:ietf:params:xml:ns:yang:\
+                ietf-rib-extension">
+                <next-hop-address>2001:db8:cccc::2222</next-hop-address>
+                <metric>200</metric>
+               </repair-path>
+             </next-hop>
+             <route-preference>120</route-preference>
+             <source-protocol xmlns:rip="urn:ietf:params:xml:ns:yang:\
+               ietf-rip">rip:rip</source-protocol>
+             <last-updated>2015-10-24T18:02:45+02:00</last-updated>
+           </route>
+         </routes>
+       </rib>
+     </ribs>
+   </routing>
+
+   The following is the same example using JSON format [RFC7951].
+
+   {
+    "ietf-routing:routing": {
+      "control-plane-protocols": {
+        "control-plane-protocol": [
+          {
+            "type": "static",
+            "name": "static-routing-protocol",
+            "static-routes": {
+              "ietf-ipv4-unicast-routing:ipv4": {
+                "route": [
+                  {
+                    "destination-prefix": "0.0.0.0/0",
+                    "next-hop": {
+                      "next-hop-address": "192.0.2.2",
+                      "ietf-rib-extension:preference": 30,
+                      "ietf-rib-extension:tag": 99
+                    }
+                  }
+                ]
+              },
+              "ietf-ipv6-unicast-routing:ipv6": {
+                "route": [
+                  {
+                    "destination-prefix": "::/0",
+                    "next-hop": {
+                      "next-hop-address": "2001:db8:aaaa::1111",
+                      "ietf-rib-extension:preference": 30,
+                      "ietf-rib-extension:tag": 66
+                    }
+                  }
+                ]
+              }
+            }
+          }
+        ]
+      },
+      "ribs": {
+        "rib": [
+          {
+            "name": "ipv4-primary",
+            "address-family": "ietf-ipv4-unicast-routing:ipv4-unicast",
+            "default-rib": true,
+            "routes": {
+              "route": [
+                {
+                  "next-hop": {
+                    "ietf-ipv4-unicast-routing:next-hop-address": \
+                    "192.0.2.2"
+                  },
+                  "route-preference": 5,
+                  "source-protocol": "static",
+                  "last-updated": "2015-10-24T18:02:45+02:00",
+                  "ietf-ipv4-unicast-routing:destination-prefix": \
+                  "0.0.0.0/0"
+                },
+                {
+                  "next-hop": {
+                    "ietf-rib-extension:repair-path": {
+                      "next-hop-address": "203.0.113.1",
+                      "metric": 200
+                    },
+                    "ietf-ipv4-unicast-routing:next-hop-address": \
+                    "192.0.2.2"
+                  },
+                  "route-preference": 120,
+                  "source-protocol": "ietf-rip:rip",
+                  "last-updated": "2015-10-24T18:02:45+02:00",
+                  "ietf-ipv4-unicast-routing:destination-prefix": \
+                  "198.51.100.0/24"
+                }
+              ]
+            }
+          },
+          {
+            "name": "ipv6-primary",
+            "address-family": "ietf-ipv6-unicast-routing:ipv6-unicast",
+            "default-rib": true,
+            "routes": {
+              "route": [
+                {
+                  "next-hop": {
+                    "ietf-ipv6-unicast-routing:next-hop-address": \
+                    "2001:db8:aaaa::1111"
+                  },
+                  "route-preference": 5,
+                  "source-protocol": "static",
+                  "last-updated": "2015-10-24T18:02:45+02:00",
+                  "ietf-ipv6-unicast-routing:destination-prefix": "::/0"
+                },
+                {
+                  "next-hop": {
+                    "ietf-rib-extension:repair-path": {
+                      "next-hop-address": "2001:db8:cccc::2222",
+                      "metric": 200
+                    },
+                    "ietf-ipv6-unicast-routing:next-hop-address": \
+                    "2001:db8:aaaa::1111"
+                  },
+                  "route-preference": 120,
+                  "source-protocol": "ietf-rip:rip",
+                  "last-updated": "2015-10-24T18:02:45+02:00",
+                  "ietf-ipv6-unicast-routing:destination-prefix": \
+                  "2001:db8:bbbb::/64"
+                }
+              ]
+            }
+          }
+        ]
+      }
+    }
+   }
+
+Acknowledgments
+
+   The authors wish to thank Les Ginsberg, Krishna Deevi, and Suyoung
+   Yoon for their helpful comments and suggestions.
+
+   The authors wish to thank Tom Petch, Rob Wilton, Chris Hopps, Martin
+   Björklund, Jeffrey Zhang, Éric Vyncke, Lars Eggert, and Bo Wu for
+   their reviews and comments.
+
+Authors' Addresses
+
+   Acee Lindem
+   LabN Consulting, L.L.C.
+   301 Midenhall Way
+   Cary, NC 27513
+   United States of America
+   Email: acee.ietf@gmail.com
+
+
+   Yingzhen Qu
+   Futurewei Technologies
+   2330 Central Expressway
+   Santa Clara, CA 95050
+   United States of America
+   Email: yingzhen.qu@futurewei.com