Internet Engineering Task Force (IETF)                             Y. Qu
Request for Comments: 9067                                     Futurewei
Category: Standards Track                                    J. Tantsura
ISSN: 2070-1721                                                Microsoft
                                                               A. Lindem
                                                                   Cisco
                                                                  X. Liu
                                                          Volta Networks
                                                            October 2021


                  A YANG Data Model for Routing Policy

Abstract

   This document defines a YANG data model for configuring and managing
   routing policies in a vendor-neutral way.  The model provides a
   generic routing policy framework that can be extended for specific
   routing protocols using the YANG 'augment' mechanism.

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/rfc9067.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
     1.1.  Goals and Approach
   2.  Terminology and Notation
     2.1.  Tree Diagrams
     2.2.  Prefixes in Data Node Names
   3.  Model Overview
   4.  Route Policy Expression
     4.1.  Defined Sets for Policy Matching
     4.2.  Policy Conditions
     4.3.  Policy Actions
     4.4.  Policy Subroutines
   5.  Policy Evaluation
   6.  Applying Routing Policy
   7.  YANG Module and Tree
     7.1.  Routing Policy Model Tree
     7.2.  Routing Policy Model
   8.  Security Considerations
   9.  IANA Considerations
   10. References
     10.1.  Normative References
     10.2.  Informative References
   Appendix A.  Routing Protocol-Specific Policies
   Appendix B.  Policy Examples
   Acknowledgements
   Authors' Addresses

1.  Introduction

   This document describes a YANG data model [RFC7950] for routing
   policy configuration based on operational usage and best practices in
   a variety of service provider networks.  The model is intended to be
   vendor neutral to allow operators to manage policy configuration
   consistently in environments with routers supplied by multiple
   vendors.

   The YANG modules in this document conform to the Network Management
   Datastore Architecture (NMDA) [RFC8342].

1.1.  Goals and Approach

   This model does not aim to be feature complete; it is a subset of the
   policy configuration parameters available in a variety of vendor
   implementations but supports widely used constructs for managing how
   routes are imported, exported, and modified across different routing
   protocols.  The model development approach has been to examine actual
   policy configurations in use across several operator networks.
   Hence, the focus is on enabling policy configuration capabilities and
   structure that are in wide use.

   Despite the differences in details of policy expressions and
   conventions in various vendor implementations, the model reflects the
   observation that a relatively simple condition-action approach can be
   readily mapped to several existing vendor implementations and also
   gives operators a familiar and straightforward way to express policy.
   A side effect of this design decision is that other methods for
   expressing policies are not considered.

   Consistent with the goal to produce a data model that is vendor
   neutral, only policy expressions that are deemed to be widely
   available in prevalent implementations are included in the model.
   Those configuration items that are only available from a single
   implementation are omitted from the model with the expectation they
   will be available in separate vendor-provided modules that augment
   the current model.

2.  Terminology and Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   Routing policy:  A routing policy defines how routes are imported,
      exported, modified, and advertised between routing protocol
      instances or within a single routing protocol instance.

   Policy chain:  A policy chain is a sequence of policy definitions.
      They can be referenced from different contexts.

   Policy statement:  Policy statements consist of a set of conditions
      and actions (either of which may be empty).

   The following terms are defined in [RFC8342]:

   *  client

   *  server

   *  configuration

   *  system state

   *  operational state

   *  intended configuration

   The following terms are defined in [RFC7950]:

   *  action

   *  augment

   *  container

   *  container with presence

   *  data model

   *  data node

   *  feature

   *  leaf

   *  list

   *  mandatory node

   *  module

   *  schema tree

   *  RPC (Remote Procedure Call) operation

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 if it is clear in which YANG
   module each name is defined given the context.  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] |
                 +--------+-----------------+-----------+
                 | yang   | ietf-yang-types | [RFC6991] |
                 +--------+-----------------+-----------+
                 | inet   | ietf-inet-types | [RFC6991] |
                 +--------+-----------------+-----------+

                   Table 1: Prefixes and Corresponding
                               YANG Modules

3.  Model Overview

   The routing policy module has three main parts:

   *  A generic framework is provided to express policies as sets of
      related conditions and actions.  This includes match sets and
      actions that are useful across many routing protocols.

   *  A structure that allows routing protocol models to add protocol-
      specific policy conditions and actions through YANG augmentations
      is also provided.  There is a complete example of this for BGP
      [RFC4271] policies in the proposed vendor-neutral BGP data model
      [IDR-BGP-MODEL].  Appendix A provides an example of how an
      augmentation for BGP policies might be accomplished.  Note that
      this section is not normative, as the BGP model is still evolving.

   *  Finally, a reusable grouping is defined for attaching import and
      export rules in the context of routing configuration for different
      protocols, Virtual Routing and Forwarding (VRF) instances, etc.
      This also enables the creation of policy chains and the expression
      of default policy behavior.  In this document, policy chains are
      sequences of policy definitions that are applied in order
      (described in Section 4).

   The module makes use of the standard Internet types, such as IP
   addresses, autonomous system numbers, etc., defined in RFC 6991
   [RFC6991].

4.  Route Policy Expression

   Policies are expressed as a sequence of top-level policy definitions,
   each of which consists of a sequence of policy statements.  Policy
   statements in turn consist of simple condition-action tuples.
   Conditions may include multiple match or comparison operations, and
   similarly, actions may include multiple changes to route attributes
   or indicate a final disposition of accepting or rejecting the route.
   This structure is shown below.

     +--rw routing-policy
        +--rw policy-definitions
           +--ro match-modified-attributes?   boolean
           +--rw policy-definition* [name]
              +--rw name          string
              +--rw statements
                 +--rw statement* [name]
                    +--rw name          string
                    +--rw conditions
                    |     ...
                    +--rw actions
                          ...

4.1.  Defined Sets for Policy Matching

   The model provides a collection of generic sets that can be used for
   matching in policy conditions.  These sets are applicable for route
   selection across multiple routing protocols.  They may be further
   augmented by protocol-specific models that have their own defined
   sets.  The defined sets include:

   prefix sets:  Each prefix set defines a set of IP prefixes, each with
      an associated IP prefix and netmask range (or exact length).

   neighbor sets:  Each neighbor set defines a set of neighboring nodes
      by their IP addresses.  A neighbor set is used for selecting
      routes based on the neighbors advertising the routes.

   tag sets:  Each tag set defines a set of generic tag values that can
      be used in matches for selecting routes.

   The model structure for defined sets is shown below.

       +--rw routing-policy
          +--rw defined-sets
          |  +--rw prefix-sets
          |  |  +--rw prefix-set* [name]
          |  |     +--rw name        string
          |  |     +--rw mode?       enumeration
          |  |     +--rw prefixes
          |  |        +--rw prefix-list* [ip-prefix mask-length-lower
          |  |                            mask-length-upper]
          |  |           +--rw ip-prefix           inet:ip-prefix
          |  |           +--rw mask-length-lower    uint8
          |  |           +--rw mask-length-upper    uint8
          |  +--rw neighbor-sets
          |  |  +--rw neighbor-set* [name]
          |  |     +--rw name       string
          |  |     +--rw address*   inet:ip-address
          |  +--rw tag-sets
          |     +--rw tag-set* [name]
          |        +--rw name         string
          |        +--rw tag-value*   tag-type

4.2.  Policy Conditions

   Policy statements consist of a set of conditions and actions (either
   of which may be empty).  Conditions are used to match route
   attributes against a defined set (e.g., a prefix set) or to compare
   attributes against a specific value.

   Match conditions may be further modified using the match-set-options
   configuration, which allows network operators to change the behavior
   of a match.  Three options are supported:

   'all':  Match is true only if the given value matches all members of
      the set.

   'any':  Match is true if the given value matches any member of the
      set.

   'invert':  Match is true if the given value does not match any member
      of the given set.

   Not all options are appropriate for matching against all defined sets
   (e.g., match 'all' in a prefix set does not make sense).  In the
   model, a restricted set of match options is used where applicable.

   Comparison conditions may similarly use options to change how route
   attributes should be tested, e.g., for equality or inequality,
   against a given value.

   While most policy conditions will be added by individual routing
   protocol models via augmentation, this routing policy model includes
   several generic match conditions and the ability to test which
   protocol or mechanism installed a route (e.g., BGP, IGP, static,
   etc.).  The conditions included in the model are shown below.

     +--rw routing-policy
        +--rw policy-definitions
           +--rw policy-definition* [name]
              +--rw name          string
              +--rw statements
                 +--rw statement* [name]
                    +--rw conditions
                    |  +--rw call-policy?
                    |  +--rw source-protocol?
                    |  +--rw match-interface
                    |  |  +--rw interface?
                    |  +--rw match-prefix-set
                    |  |  +--rw prefix-set?
                    |  |  +--rw match-set-options?
                    |  +--rw match-neighbor-set
                    |  |  +--rw neighbor-set?
                    |  +--rw match-tag-set
                    |  |  +--rw tag-set?
                    |  |  +--rw match-set-options?
                    |  +--rw match-route-type
                    |     +--rw route-type*

4.3.  Policy Actions

   When policy conditions are satisfied, policy actions are used to set
   various attributes of the route being processed or to indicate the
   final disposition of the route, i.e., accept or reject.

   Similar to policy conditions, the routing policy model includes
   generic actions in addition to the basic route disposition actions.
   These are shown below.

     +--rw routing-policy
        +--rw policy-definitions
           +--rw policy-definition* [name]
              +--rw statements
                 +--rw statement* [name]
                    +--rw actions
                       +--rw policy-result?   policy-result-type
                       +--rw set-metric
                       |  +--rw metric-modification?
                       |  |         metric-modification-type
                       |  +--rw metric?                 uint32
                       +--rw set-metric-type
                       |  +--rw metric-type?   identityref
                       +--rw set-route-level
                       |  +--rw route-level?   identityref
                       +--rw set-route-preference?      uint16
                       +--rw set-tag?               tag-type
                       +--rw set-application-tag?   tag-type

4.4.  Policy Subroutines

   Policy 'subroutines' (or nested policies) are supported by allowing
   policy statement conditions to reference other policy definitions
   using the call-policy configuration.  Called policies apply their
   conditions and actions before returning to the calling policy
   statement and resuming evaluation.  The outcome of the called policy
   affects the evaluation of the calling policy.  If the called policy
   results in an accept-route, then the subroutine returns an effective
   Boolean true value to the calling policy.  For the calling policy,
   this is equivalent to a condition statement evaluating to a true
   value, thus the calling party continues in its evaluation of the
   policy (see Section 5).  Note that the called policy may also modify
   attributes of the route in its action statements.  Similarly, a
   reject-route action returns false, and the calling policy evaluation
   will be affected accordingly.  When the end of the subroutine policy
   statements is reached, the default route disposition action is
   returned (i.e., Boolean false for reject-route).  Consequently, a
   subroutine cannot explicitly accept or reject a route.  Rather, the
   called policy returns Boolean true if its outcome is accept-route or
   Boolean false if its outcome is reject-route.  Route acceptance or
   rejection is solely determined by the top-level policy.

   Note that the called policy may itself call other policies (subject
   to implementation limitations).  The model does not prescribe a
   nesting depth because this varies among implementations.  For
   example, an implementation may only support a single level of
   subroutine recursion.  As with any routing policy construction, care
   must be taken with nested policies to ensure that the effective
   return value results in the intended behavior.  Nested policies are a
   convenience in many routing policy constructions, but creating
   policies nested beyond a small number of levels (e.g., two to three)
   is discouraged.  Also, implementations MUST perform validation to
   ensure that there is no recursion among nested routing policies.

5.  Policy Evaluation

   Evaluation of each policy definition proceeds by evaluating its
   individual policy statements in the order that they are defined.
   When all the condition statements in a policy statement are
   satisfied, the corresponding action statements are executed.  If the
   actions include either accept-route or reject-route actions,
   evaluation of the current policy definition stops, and no further
   policy statement is evaluated.  If there are multiple policies in the
   policy chain, subsequent policies are not evaluated.  Policy chains
   are sequences of policy definitions (as described in Section 4).

   If the conditions are not satisfied, then evaluation proceeds to the
   next policy statement.  If none of the policy statement conditions
   are satisfied, then evaluation of the current policy definition
   stops, and the next policy definition in the chain is evaluated.
   When the end of the policy chain is reached, the default route
   disposition action is performed (i.e., reject-route unless an
   alternate default action is specified for the chain).

   Whether the route's pre-policy attributes are used for testing policy
   statement conditions is dependent on the implementation-specific
   value of the match-modified-attributes leaf.  If match-modified-
   attributes is false and actions modify route attributes, these
   modifications are not used for policy statement conditions.
   Conversely, if match-modified-attributes is true and actions modify
   the policy application-specific attributes, the attributes as
   modified by the policy are used for policy condition statements.

6.  Applying Routing Policy

   Routing policy is applied by defining and attaching policy chains in
   various routing contexts.  Policy chains are sequences of policy
   definitions (described in Section 4).  They can be referenced from
   different contexts.  For example, a policy chain could be associated
   with a routing protocol and used to control its interaction with its
   protocol peers, or it could be used to control the interaction
   between a routing protocol and the local routing information base.  A
   policy chain has an associated direction (import or export) with
   respect to the context in which it is referenced.

   The routing policy model defines an apply-policy grouping that can be
   imported and used by other models.  As shown below, it allows
   definition of import and export policy chains, as well as specifies
   the default route disposition to be used when no policy definition in
   the chain results in a final decision.

         +--rw apply-policy
         |  +--rw import-policy*
         |  +--rw default-import-policy?   default-policy-type
         |  +--rw export-policy*
         |  +--rw default-export-policy?   default-policy-type

   The default policy defined by the model is to reject the route for
   both import and export policies.

7.  YANG Module and Tree

7.1.  Routing Policy Model Tree

   The tree of the routing policy model is shown below.

   module: ietf-routing-policy
     +--rw routing-policy
        +--rw defined-sets
        |  +--rw prefix-sets
        |  |  +--rw prefix-set* [name mode]
        |  |     +--rw name        string
        |  |     +--rw mode        enumeration
        |  |     +--rw prefixes
        |  |        +--rw prefix-list* [ip-prefix mask-length-lower
        |  |                            mask-length-upper]
        |  |           +--rw ip-prefix            inet:ip-prefix
        |  |           +--rw mask-length-lower    uint8
        |  |           +--rw mask-length-upper    uint8
        |  +--rw neighbor-sets
        |  |  +--rw neighbor-set* [name]
        |  |     +--rw name       string
        |  |     +--rw address*   inet:ip-address
        |  +--rw tag-sets
        |     +--rw tag-set* [name]
        |        +--rw name         string
        |        +--rw tag-value*   tag-type
        +--rw policy-definitions
           +--ro match-modified-attributes?   boolean
           +--rw policy-definition* [name]
              +--rw name          string
              +--rw statements
                 +--rw statement* [name]
                    +--rw name          string
                    +--rw conditions
                    |  +--rw call-policy?       -> ../../../../../..
                    |                           /policy-definitions
                    |                           /policy-definition/name
                    |  +--rw source-protocol?      identityref
                    |  +--rw match-interface
                    |  |  +--rw interface?      if:interface-ref
                    |  +--rw match-prefix-set
                    |  |  +--rw prefix-set?     -> ../../../../../../..
                    |  |                        /defined-sets
                    |  |                        /prefix-sets
                    |  |                        /prefix-set/name
                    |  |  +--rw match-set-options?
                    |  |                        match-set-options-type
                    |  +--rw match-neighbor-set
                    |  |  +--rw neighbor-set?   -> ../../../../../../..
                    |  |                        /defined-sets
                    |  |                        /neighbor-sets
                    |  |                        /neighbor-set/name
                    |  +--rw match-tag-set
                    |  |  +--rw tag-set?        -> ../../../../../../..
                    |  |                        /defined-sets/tag-sets
                    |  |                        /tag-set/name
                    |  |  +--rw match-set-options?
                    |  |                        match-set-options-type
                    |  +--rw match-route-type
                    |     +--rw route-type*     identityref
                    +--rw actions
                       +--rw policy-result?         policy-result-type
                       +--rw set-metric
                       |  +--rw metric-modification?
                       |                        metric-modification-type
                       |  +--rw metric?                uint32
                       +--rw set-metric-type
                       |  +--rw metric-type?   identityref
                       +--rw set-route-level
                       |  +--rw route-level?   identityref
                       +--rw set-route-preference?        uint16
                       +--rw set-tag?               tag-type
                       +--rw set-application-tag?   tag-type

7.2.  Routing Policy Model

   The following RFCs are not referenced in the document text but are
   referenced in the ietf-routing-policy.yang module: [RFC2328],
   [RFC3101], [RFC5130], [RFC5302], [RFC6991], and [RFC8343].

   <CODE BEGINS> file "ietf-routing-policy@2021-10-11.yang"
   module ietf-routing-policy {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-routing-policy";
     prefix rt-pol;

     import ietf-inet-types {
       prefix inet;
       reference
         "RFC 6991: Common YANG Data Types";
     }
     import ietf-yang-types {
       prefix yang;
       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)";
     }

     organization
       "IETF RTGWG - Routing Area Working Group";
     contact
       "WG Web:   <https://datatracker.ietf.org/wg/rtgwg/>
        WG List:  <mailto: rtgwg@ietf.org>

        Editors:  Yingzhen Qu
                  <mailto: yingzhen.qu@futurewei.com>
                  Jeff Tantsura
                  <mailto: jefftant.ietf@gmail.com>
                  Acee Lindem
                  <mailto: acee@cisco.com>
                  Xufeng Liu
                  <mailto: xufeng.liu.ietf@gmail.com>";
     description
       "This module describes a YANG data model for routing policy
        configuration. It is a limited subset of all of the policy
        configuration parameters available in the variety of vendor
        implementations, but supports widely used constructs for
        managing how routes are imported, exported, modified, and
        advertised across different routing protocol instances or
        within a single routing protocol instance.  This module is
        intended to be used in conjunction with routing protocol
        configuration modules (e.g., BGP) defined in other models.

        This YANG module conforms to the Network Management
        Datastore Architecture (NMDA), as described in RFC 8342.

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',
        'MAY', and 'OPTIONAL' in this document are to be interpreted as
        described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
        they appear in all capitals, as shown here.

        Copyright (c) 2021 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

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

        This version of this YANG module is part of RFC 9067;
        see the RFC itself for full legal notices.";

     reference
       "RFC 9067: A YANG Data Model for Routing Policy.";

     revision 2021-10-11 {
       description
         "Initial revision.";
       reference
         "RFC 9067: A YANG Data Model for Routing Policy.";
     }

     /* Identities */

     identity metric-type {
       description
         "Base identity for route metric types.";
     }

     identity ospf-type-1-metric {
       base metric-type;
       description
         "Identity for the OSPF type 1 external metric types.  It
          is only applicable to OSPF routes.";
       reference
         "RFC 2328: OSPF Version 2";
     }

     identity ospf-type-2-metric {
       base metric-type;
       description
         "Identity for the OSPF type 2 external metric types.  It
          is only applicable to OSPF routes.";
       reference
         "RFC 2328: OSPF Version 2";
     }

     identity isis-internal-metric {
       base metric-type;
       description
         "Identity for the IS-IS internal metric types.  It is only
          applicable to IS-IS routes.";
       reference
         "RFC 5302: Domain-Wide Prefix Distribution with
          Two-Level IS-IS";
     }

     identity isis-external-metric {
       base metric-type;
       description
         "Identity for the IS-IS external metric types.  It is only
          applicable to IS-IS routes.";
       reference
         "RFC 5302: Domain-Wide Prefix Distribution with
          Two-Level IS-IS";
     }

     identity route-level {
       description
         "Base identity for route import level.";
     }

     identity ospf-normal {
       base route-level;
       description
         "Identity for OSPF importation into normal areas.
          It is only applicable to routes imported
          into the OSPF protocol.";
       reference
         "RFC 2328: OSPF Version 2";
     }

     identity ospf-nssa-only {
       base route-level;
       description
         "Identity for the OSPF Not-So-Stubby Area (NSSA) area
          importation.  It is only applicable to routes imported
          into the OSPF protocol.";
       reference
         "RFC 3101: The OSPF Not-So-Stubby Area (NSSA) Option";
     }

     identity ospf-normal-nssa {
       base route-level;
       description
         "Identity for OSPF importation into both normal and NSSA
          areas.  It is only applicable to routes imported into
          the OSPF protocol.";
       reference
         "RFC 3101: The OSPF Not-So-Stubby Area (NSSA) Option";
     }

     identity isis-level-1 {
       base route-level;
       description
         "Identity for IS-IS Level 1 area importation.  It is only
          applicable to routes imported into the IS-IS protocol.";
       reference
         "RFC 5302: Domain-Wide Prefix Distribution with
          Two-Level IS-IS";
     }

     identity isis-level-2 {
       base route-level;
       description
         "Identity for IS-IS Level 2 area importation.  It is only
          applicable to routes imported into the IS-IS protocol.";
       reference
         "RFC 5302: Domain-Wide Prefix Distribution with
          Two-Level IS-IS";
     }

     identity isis-level-1-2 {
       base route-level;
       description
         "Identity for IS-IS importation into both Level 1 and Level 2
          areas.  It is only applicable to routes imported into the
          IS-IS protocol.";
       reference
         "RFC 5302: Domain-Wide Prefix Distribution with
          Two-Level IS-IS";
     }

     identity proto-route-type {
       description
         "Base identity for route type within a protocol.";
     }

     identity isis-level-1-type {
       base proto-route-type;
       description
         "Identity for IS-IS Level 1 route type.  It is only
          applicable to IS-IS routes.";
       reference
         "RFC 5302: Domain-Wide Prefix Distribution with
          Two-Level IS-IS";
     }

     identity isis-level-2-type {
       base proto-route-type;
       description
         "Identity for IS-IS Level 2 route type.  It is only
          applicable to IS-IS routes.";
       reference
         "RFC 5302: Domain-Wide Prefix Distribution with
          Two-Level IS-IS";
     }

     identity ospf-internal-type {
       base proto-route-type;
       description
         "Identity for OSPF intra-area or inter-area route type.
          It is only applicable to OSPF routes.";
       reference
         "RFC 2328: OSPF Version 2";
     }

     identity ospf-external-type {
       base proto-route-type;
       description
         "Identity for OSPF external type 1/2 route type.
          It is only applicable to OSPF routes.";
       reference
         "RFC 2328: OSPF Version 2";
     }

     identity ospf-external-t1-type {
       base ospf-external-type;
       description
         "Identity for OSPF external type 1 route type.
          It is only applicable to OSPF routes.";
       reference
         "RFC 2328: OSPF Version 2";
     }

     identity ospf-external-t2-type {
       base ospf-external-type;
       description
         "Identity for OSPF external type 2 route type.
          It is only applicable to OSPF routes.";
       reference
         "RFC 2328: OSPF Version 2";
     }

     identity ospf-nssa-type {
       base proto-route-type;
       description
         "Identity for OSPF NSSA type 1/2 route type.
          It is only applicable to OSPF routes.";
       reference
         "RFC 3101: The OSPF Not-So-Stubby Area (NSSA) Option";
     }

     identity ospf-nssa-t1-type {
       base ospf-nssa-type;
       description
         "Identity for OSPF NSSA type 1 route type.
          It is only applicable to OSPF routes.";
       reference
         "RFC 3101: The OSPF Not-So-Stubby Area (NSSA) Option";
     }

     identity ospf-nssa-t2-type {
       base ospf-nssa-type;
       description
         "Identity for OSPF NSSA type 2 route type.
          It is only applicable to OSPF routes.";
       reference
         "RFC 3101: The OSPF Not-So-Stubby Area (NSSA) Option";
     }

     identity bgp-internal {
       base proto-route-type;
       description
         "Identity for routes learned from internal BGP (IBGP).
          It is only applicable to BGP routes.";
       reference
         "RFC 4271: A Border Gateway Protocol 4 (BGP-4)";
     }

     identity bgp-external {
       base proto-route-type;
       description
         "Identity for routes learned from external BGP (EBGP).
          It is only applicable to BGP routes.";
       reference
         "RFC 4271: A Border Gateway Protocol 4 (BGP-4)";
     }

     /* Type Definitions */

     typedef default-policy-type {
       type enumeration {
         enum accept-route {
           description
             "Default policy to accept the route.";
         }
         enum reject-route {
           description
             "Default policy to reject the route.";
         }
       }
       description
         "Type used to specify route disposition in
          a policy chain.  This typedef is used in
          the default import and export policy.";
     }

     typedef policy-result-type {
       type enumeration {
         enum accept-route {
           description
             "Policy accepts the route.";
         }
         enum reject-route {
           description
             "Policy rejects the route.";
         }
       }
       description
         "Type used to specify route disposition in
          a policy chain.";
     }

     typedef tag-type {
       type union {
         type uint32;
         type yang:hex-string;
       }
       description
         "Type for expressing route tags on a local system,
          including IS-IS and OSPF; may be expressed as either decimal
          or hexadecimal integer.";
       reference
         "RFC 2328: OSPF Version 2
          RFC 5130: A Policy Control Mechanism in IS-IS Using
                    Administrative Tags";
     }

     typedef match-set-options-type {
       type enumeration {
         enum any {
           description
             "Match is true if given value matches any member
              of the defined set.";
         }
         enum all {
           description
             "Match is true if given value matches all
              members of the defined set.";
         }
         enum invert {
           description
             "Match is true if given value does not match any
              member of the defined set.";
         }
       }
       default "any";
       description
         "Options that govern the behavior of a match statement.  The
          default behavior is any, i.e., the given value matches any
          of the members of the defined set.";
     }

     typedef metric-modification-type {
       type enumeration {
         enum set-metric {
           description
             "Set the metric to the specified value.";
         }
         enum add-metric {
           description
             "Add the specified value to the existing metric.
              If the result overflows the maximum metric
              (0xffffffff), set the metric to the maximum.";
         }
         enum subtract-metric {
           description
             "Subtract the specified value from the existing metric.  If
              the result is less than 0, set the metric to 0.";
         }
       }
       description
         "Type used to specify how to set the metric given the
          specified value.";
     }

     /* Groupings */

     grouping prefix {
       description
         "Configuration data for a prefix definition.

          The combination of mask-length-lower and mask-length-upper
          define a range for the mask length or single 'exact'
          length if mask-length-lower and mask-length-upper are
          equal.

          Example: 192.0.2.0/24 through 192.0.2.0/26 would be
          expressed as prefix: 192.0.2.0/24,
                       mask-length-lower=24,
                       mask-length-upper=26

          Example: 192.0.2.0/24 (an exact match) would be
          expressed as prefix: 192.0.2.0/24,
                       mask-length-lower=24,
                       mask-length-upper=24

          Example: 2001:DB8::/32 through 2001:DB8::/64 would be
          expressed as prefix: 2001:DB8::/32,
                       mask-length-lower=32,
                       mask-length-upper=64";
       leaf ip-prefix {
         type inet:ip-prefix;
         mandatory true;
         description
           "The IP prefix represented as an IPv6 or IPv4 network
            number followed by a prefix length with an intervening
            slash character as a delimiter.  All members of the
            prefix-set MUST be of the same address family as the
            prefix-set mode.";
       }
       leaf mask-length-lower {
         type uint8 {
           range "0..128";
         }
         description
           "Mask length range lower bound.  It MUST NOT be less than
            the prefix length defined in ip-prefix.";
       }
       leaf mask-length-upper {
         type uint8 {
           range "1..128";
         }
         must '../mask-length-upper >= ../mask-length-lower' {
           error-message "The upper bound MUST NOT be less "
                       + "than lower bound.";
         }
         description
           "Mask length range upper bound.  It MUST NOT be less than
            lower bound.";
       }
     }

     grouping match-set-options-group {
       description
         "Grouping containing options relating to how a particular set
          will be matched.";
       leaf match-set-options {
         type match-set-options-type;
         description
           "Optional parameter that governs the behavior of the
            match operation.";
       }
     }

     grouping match-set-options-restricted-group {
       description
         "Grouping for a restricted set of match operation
          modifiers.";
       leaf match-set-options {
         type match-set-options-type {
           enum any {
             description
               "Match is true if given value matches any
                member of the defined set.";
           }
           enum invert {
             description
               "Match is true if given value does not match
                any member of the defined set.";
           }
         }
         description
           "Optional parameter that governs the behavior of the
            match operation.  This leaf only supports
            the 'any' and 'invert' match options.
            Matching on 'all' is not supported.";
       }
     }

     grouping apply-policy-group {
       description
         "Top-level container for routing policy applications.  This
          grouping is intended to be used in routing models where
          needed.";
       container apply-policy {
         description
           "Anchor point for routing policies in the model.
            Import and export policies are with respect to the local
            routing table, i.e., export (send) and import (receive),
            depending on the context.";
         leaf-list import-policy {
           type leafref {
             path "/rt-pol:routing-policy/rt-pol:policy-definitions/"
                + "rt-pol:policy-definition/rt-pol:name";
             require-instance true;
           }
           ordered-by user;
           description
             "List of policy names in sequence to be applied on
              receiving redistributed routes from another routing
              protocol or receiving a routing update in the current
              context, e.g., for the current peer group, neighbor,
              address family, etc.";
         }
         leaf default-import-policy {
           type default-policy-type;
           default "reject-route";
           description
             "Explicitly set a default policy if no policy definition
              in the import policy chain is satisfied.";
         }
         leaf-list export-policy {
           type leafref {
             path "/rt-pol:routing-policy/rt-pol:policy-definitions/"
                + "rt-pol:policy-definition/rt-pol:name";
             require-instance true;
           }
           ordered-by user;
           description
             "List of policy names in sequence to be applied on
              redistributing routes from one routing protocol to another
              or sending a routing update in the current context, e.g.,
              for the current peer group, neighbor, address family,
              etc.";
         }
         leaf default-export-policy {
           type default-policy-type;
           default "reject-route";
           description
             "Explicitly set a default policy if no policy definition
              in the export policy chain is satisfied.";
         }
       }
     }

     container routing-policy {
       description
         "Top-level container for all routing policy.";
       container defined-sets {
         description
           "Predefined sets of attributes used in policy match
            statements.";
         container prefix-sets {
           description
             "Data definitions for a list of IPv4 or IPv6
              prefixes that are matched as part of a policy.";
           list prefix-set {
             key "name mode";
             description
               "List of the defined prefix sets";
             leaf name {
               type string;
               description
                 "Name of the prefix set; this is used as a label to
                  reference the set in match conditions.";
             }
             leaf mode {
               type enumeration {
                 enum ipv4 {
                   description
                     "Prefix set contains IPv4 prefixes only.";
                 }
                 enum ipv6 {
                   description
                     "Prefix set contains IPv6 prefixes only.";
                 }
               }
               description
                 "Indicates the mode of the prefix set in terms of
                  which address families (IPv4 or IPv6) are present.
                  The mode provides a hint; all prefixes MUST be of
                  the indicated type.  The device MUST validate
                  all prefixes and reject the configuration if there
                  is a discrepancy.";
             }
             container prefixes {
               description
                 "Container for the list of prefixes in a policy
                  prefix list.  Since individual prefixes do not have
                  unique actions, the order in which the prefix in
                  prefix-list are matched has no impact on the outcome
                  and is left to the implementation.  A given prefix-set
                  condition is satisfied if the input prefix matches
                  any of the prefixes in the prefix-set.";
               list prefix-list {
                 key "ip-prefix mask-length-lower mask-length-upper";
                 description
                   "List of prefixes in the prefix set.";
                 uses prefix;
               }
             }
           }
         }
         container neighbor-sets {
           description
             "Data definition for a list of IPv4 or IPv6
              neighbors that can be matched in a routing policy.";
           list neighbor-set {
             key "name";
             description
               "List of defined neighbor sets for use in policies.";
             leaf name {
               type string;
               description
                 "Name of the neighbor set; this is used as a label
                  to reference the set in match conditions.";
             }
             leaf-list address {
               type inet:ip-address;
               description
                 "List of IP addresses in the neighbor set.";
             }
           }
         }
         container tag-sets {
           description
             "Data definitions for a list of tags that can
              be matched in policies.";
           list tag-set {
             key "name";
             description
               "List of tag set definitions.";
             leaf name {
               type string;
               description
                 "Name of the tag set; this is used as a label to
                  reference the set in match conditions.";
             }
             leaf-list tag-value {
               type tag-type;
               description
                 "Value of the tag set member.";
             }
           }
         }
       }
       container policy-definitions {
         description
           "Enclosing container for the list of top-level policy
            definitions.";
         leaf match-modified-attributes {
           type boolean;
           config false;
           description
             "This boolean value dictates whether matches are performed
              on the actual route attributes or route attributes
              modified by policy statements preceding the match.";
         }
         list policy-definition {
           key "name";
           description
             "List of top-level policy definitions, keyed by unique
              name.  These policy definitions are expected to be
              referenced (by name) in policy chains specified in
              import or export configuration statements.";
           leaf name {
             type string;
             description
               "Name of the top-level policy definition; this name
                is used in references to the current policy.";
           }
           container statements {
             description
               "Enclosing container for policy statements.";
             list statement {
               key "name";
               ordered-by user;
               description
                 "Policy statements group conditions and actions
                  within a policy definition.  They are evaluated in
                  the order specified.";
               leaf name {
                 type string;
                 description
                   "Name of the policy statement.";
               }
               container conditions {
                 description
                   "Condition statements for the current policy
                    statement.";
                 leaf call-policy {
                   type leafref {
                     path "../../../../../../"
                        + "rt-pol:policy-definitions/"
                        + "rt-pol:policy-definition/rt-pol:name";
                     require-instance true;
                   }
                   description
                     "Applies the statements from the specified policy
                      definition and then returns control to the current
                      policy statement.  Note that the called policy
                      may itself call other policies (subject to
                      implementation limitations).  This is intended to
                      provide a policy 'subroutine' capability.  The
                      called policy SHOULD contain an explicit or a
                      default route disposition that returns an
                      effective true (accept-route) or false
                      (reject-route); otherwise, the behavior may be
                      ambiguous. The call-policy MUST NOT have been
                      previously called without returning (i.e.,
                      recursion is not allowed).";
                 }
                 leaf source-protocol {
                   type identityref {
                     base rt:control-plane-protocol;
                   }
                   description
                     "Condition to check the protocol / method used to
                      install the route into the local routing table.";
                 }
                 container match-interface {
                   leaf interface {
                     type if:interface-ref;
                     description
                       "Reference to a base interface.";
                   }
                   description
                     "Container for interface match conditions";
                 }
                 container match-prefix-set {
                   leaf prefix-set {
                     type leafref {
                       path "../../../../../../../defined-sets/"
                          + "prefix-sets/prefix-set/name";
                     }
                     description
                       "References a defined prefix set.";
                   }
                   uses match-set-options-restricted-group;
                   description
                     "Match a referenced prefix-set according to the
                      logic defined in the match-set-options leaf.";
                 }
                 container match-neighbor-set {
                   leaf neighbor-set {
                     type leafref {
                       path "../../../../../../../defined-sets/"
                          + "neighbor-sets/neighbor-set/name";
                       require-instance true;
                     }
                     description
                       "References a defined neighbor set.";
                   }
                   description
                     "Match a referenced neighbor set.";
                 }
                 container match-tag-set {
                   leaf tag-set {
                     type leafref {
                       path "../../../../../../../defined-sets/"
                          + "tag-sets/tag-set/name";
                       require-instance true;
                     }
                     description
                       "References a defined tag set.";
                   }
                   uses match-set-options-group;
                   description
                     "Match a referenced tag set according to the logic
                      defined in the match-set-options leaf.";
                 }
                 container match-route-type {
                   description
                     "This container provides route-type match
                      condition";
                   leaf-list route-type {
                     type identityref {
                       base proto-route-type;
                     }
                     description
                       "Condition to check the protocol-specific type
                        of route.  This is normally used during route
                        importation to select routes or to set
                        protocol-specific attributes based on the route
                        type.";
                   }
                 }
               }
               container actions {
                 description
                   "Top-level container for policy action
                    statements.";
                 leaf policy-result {
                   type policy-result-type;
                   description
                     "Select the final disposition for the route,
                      either accept or reject.";
                 }
                 container set-metric {
                   leaf metric-modification {
                     type metric-modification-type;
                     description
                       "Indicates how to modify the metric.";
                   }
                   leaf metric {
                     type uint32;
                     description
                       "Metric value to set, add, or subtract.";
                   }
                   description
                     "Set the metric for the route.";
                 }
                 container set-metric-type {
                   leaf metric-type {
                     type identityref {
                       base metric-type;
                     }
                     description
                       "Route metric type.";
                   }
                   description
                     "Set the metric type for the route.";
                 }
                 container set-route-level {
                   leaf route-level {
                     type identityref {
                       base route-level;
                     }
                     description
                       "Route import level.";
                   }
                   description
                     "Set the level for importation or
                      exportation of routes.";
                 }
                 leaf set-route-preference {
                   type uint16;
                   description
                     "Set the preference for the route.  It is also
                      known as 'administrative distance' and allows for
                      selecting the preferred route among routes with
                      the same destination prefix.  A smaller value is
                      more preferred.";
                 }
                 leaf set-tag {
                   type tag-type;
                   description
                     "Set the tag for the route.";
                 }
                 leaf set-application-tag {
                   type tag-type;
                   description
                     "Set the application tag for the route.
                      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.";
                 }
               }
             }
           }
         }
       }
     }
   }
   <CODE ENDS>

8.  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 this 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:

   /routing-policy/defined-sets/prefix-sets
      Modification to prefix sets could result in a Denial-of-Service
      (DoS) attack.  An attacker may try to modify prefix sets and
      redirect or drop traffic.  Redirection of traffic could be used as
      part of a more elaborate attack to either collect sensitive
      information or masquerade a service.  Additionally, a control
      plane DoS attack could be accomplished by allowing a large number
      of routes to be leaked into a routing protocol domain (e.g., BGP).

   /routing-policy/defined-sets/neighbor-sets
      Modification to the neighbor sets could be used to mount a DoS
      attack or more elaborate attack as with prefix sets.  For example,
      a DoS attack could be mounted by changing the neighbor set from
      which routes are accepted.

   /routing-policy/defined-sets/tag-sets
      Modification to the tag sets could be used to mount a DoS attack.
      Routes with certain tags might be redirected or dropped.  The
      implications are similar to prefix sets and neighbor sets.
      However, the attack may be more difficult to detect as the routing
      policy usage of route tags and intent must be understood to
      recognize the breach.  Conversely, the implications of prefix set
      or neighbor set modification are easier to recognize.

   /routing-policy/policy-definitions/policy-
   definition/statements/statement/conditions
      Modification to the conditions could be used to mount a DoS attack
      or other attack.  An attacker may change a policy condition and
      redirect or drop traffic.  As with prefix sets, neighbor sets, or
      tag sets, traffic redirection could be used as part of a more
      elaborate attack.

   /routing-policy/policy-definitions/policy-
   definition/statements/statement/actions
      Modification to actions could be used to mount a DoS attack or
      other attack.  Traffic may be redirected or dropped.  As with
      prefix sets, neighbor sets, or tag sets, traffic redirection could
      be used as part of a more elaborate attack.  Additionally, route
      attributes may be changed to mount a second-level attack that is
      more difficult to detect.

   Some of the readable data nodes in the 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:

   /routing-policy/defined-sets/prefix-sets
      Knowledge of these data nodes can be used to ascertain which local
      prefixes are susceptible to a DoS attack.

   /routing-policy/defined-sets/neighbor-sets
      Knowledge of these data nodes can be used to ascertain local
      neighbors against whom to mount a DoS attack.

   /routing-policy/policy-definitions/policy-definition/statements/
      Knowledge of these data nodes can be used to attack the local
      router with a DoS attack.  Additionally, policies and their
      attendant conditions and actions should be considered proprietary
      and disclosure could be used to ascertain partners, customers, and
      suppliers.  Furthermore, the policies themselves could represent
      intellectual property and disclosure could diminish their
      corresponding business advantage.

   Routing policy configuration has a significant impact on network
   operations, and as such, other YANG data models that reference
   routing policies are also susceptible to vulnerabilities relating to
   the YANG data nodes specified above.

9.  IANA Considerations

   IANA has registered the following URI in the "ns" subregistry of the
   "IETF XML Registry" [RFC3688]:

   URI:  urn:ietf:params:xml:ns:yang:ietf-routing-policy
   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" subregistry [RFC6020] within the "YANG Parameters" registry:

   Name:  ietf-routing-policy
   Maintained by IANA?  N
   Namespace:  urn:ietf:params:xml:ns:yang:ietf-routing-policy
   Prefix:  rt-pol
   Reference:  RFC 9067

10.  References

10.1.  Normative References

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

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

   [RFC3101]  Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
              RFC 3101, DOI 10.17487/RFC3101, January 2003,
              <https://www.rfc-editor.org/info/rfc3101>.

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

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC5130]  Previdi, S., Shand, M., Ed., and C. Martin, "A Policy
              Control Mechanism in IS-IS Using Administrative Tags",
              RFC 5130, DOI 10.17487/RFC5130, February 2008,
              <https://www.rfc-editor.org/info/rfc5130>.

   [RFC5302]  Li, T., Smit, H., and T. Przygienda, "Domain-Wide Prefix
              Distribution with Two-Level IS-IS", RFC 5302,
              DOI 10.17487/RFC5302, October 2008,
              <https://www.rfc-editor.org/info/rfc5302>.

   [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>.

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

   [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>.

   [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>.

10.2.  Informative References

   [IDR-BGP-MODEL]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
              YANG Model for Service Provider Networks", Work in
              Progress, Internet-Draft, draft-ietf-idr-bgp-model-09, 28
              June 2020, <https://datatracker.ietf.org/doc/html/draft-
              ietf-idr-bgp-model-09>.

   [W3C.REC-xml11]
              Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E.,
              Yergeau, F., and J. Cowan, "Extensible Markup Language
              (XML) 1.1 (Second Edition)", W3C Consortium
              Recommendation REC-xml11-20060816, 16 August 2006,
              <https://www.w3.org/TR/2006/REC-xml11-20060816>.

Appendix A.  Routing Protocol-Specific Policies

   Routing models that require the ability to apply routing policy may
   augment the routing policy model with protocol or other specific
   policy configuration.  The routing policy model assumes that
   additional defined sets, conditions, and actions may all be added by
   other models.

   The example below illustrates how another data model can augment
   parts of this routing policy data model.  It uses specific examples
   from draft-ietf-idr-bgp-model-09 to show in a concrete manner how the
   different pieces fit together.  This example is not normative with
   respect to [IDR-BGP-MODEL].  The model similarly augments BGP-
   specific conditions and actions in the corresponding sections of the
   routing policy model.  In the example below, the XPath prefix "bp:"
   specifies import from the ietf-bgp-policy sub-module and the XPath
   prefix "bt:" specifies import from the ietf-bgp-types sub-module
   [IDR-BGP-MODEL].

   module: ietf-routing-policy
     +--rw routing-policy
        +--rw defined-sets
        |  +--rw prefix-sets
        |  |  +--rw prefix-set* [name]
        |  |     +--rw name        string
        |  |     +--rw mode?       enumeration
        |  |     +--rw prefixes
        |  |        +--rw prefix-list* [ip-prefix mask-length-lower
        |  |                            mask-length-upper]
        |  |           +--rw ip-prefix            inet:ip-prefix
        |  |           +--rw mask-length-lower    uint8
        |  |           +--rw mask-length-upper    uint8
        |  +--rw neighbor-sets
        |  |  +--rw neighbor-set* [name]
        |  |     +--rw name       string
        |  |     +--rw address*   inet:ip-address
        |  +--rw tag-sets
        |  |  +--rw tag-set* [name]
        |  |     +--rw name         string
        |  |     +--rw tag-value*   tag-type
        |  +--rw bp:bgp-defined-sets
        |     +--rw bp:community-sets
        |     |  +--rw bp:community-set* [name]
        |     |     +--rw bp:name      string
        |     |     +--rw bp:member*   union
        |     +--rw bp:ext-community-sets
        |     |  +--rw bp:ext-community-set* [name]
        |     |     +--rw bp:name      string
        |     |     +--rw bp:member*   union
        |     +--rw bp:as-path-sets
        |        +--rw bp:as-path-set* [name]
        |           +--rw bp:name      string
        |           +--rw bp:member*   string
        +--rw policy-definitions
           +--ro match-modified-attributes?   boolean
           +--rw policy-definition* [name]
              +--rw name          string
              +--rw statements
                 +--rw statement* [name]
                    +--rw name          string
                    +--rw conditions
                    |  +--rw call-policy?
                    |  +--rw source-protocol?          identityref
                    |  +--rw match-interface
                    |  |  +--rw interface?        if:interface-ref
                    |  +--rw match-prefix-set
                    |  |  +--rw prefix-set?       prefix-set/name
                    |  |  +--rw match-set-options?
                    |  |                         match-set-options-type
                    |  +--rw match-neighbor-set
                    |  |  +--rw neighbor-set?
                    |  +--rw match-tag-set
                    |  |  +--rw tag-set?
                    |  |  +--rw match-set-options?
                    |  |                         match-set-options-type
                    |  +--rw match-route-type
                    |     +--rw route-type*     identityref
                    |  +--rw bp:bgp-conditions
                    |     +--rw bp:med-eq?       uint32
                    |     +--rw bp:origin-eq?    bt:bgp-origin-attr-type
                    |     +--rw bp:next-hop-in*  inet:ip-address-no-zone
                    |     +--rw bp:afi-safi-in*  identityref
                    |     +--rw bp:local-pref-eq?  uint32
                    |     +--rw bp:route-type?     enumeration
                    |     +--rw bp:community-count
                    |     +--rw bp:as-path-length
                    |     +--rw bp:match-community-set
                    |     |  +--rw bp:community-set?
                    |     |  +--rw bp:match-set-options?
                    |     +--rw bp:match-ext-community-set
                    |     |  +--rw bp:ext-community-set?
                    |     |  +--rw bp:match-set-options?
                    |     +--rw bp:match-as-path-set
                    |        +--rw bp:as-path-set?
                    |        +--rw bp:match-set-options?
                    +--rw actions
                       +--rw policy-result?         policy-result-type
                       +--rw set-metric
                       |  +--rw metric-modification?
                       |  +--rw metric?                uint32
                       +--rw set-metric-type
                       |  +--rw metric-type?   identityref
                       +--rw set-route-level
                       |  +--rw route-level?   identityref
                       +--rw set-route-preference?        uint16
                       +--rw set-tag?               tag-type
                       +--rw set-application-tag?   tag-type
                       +--rw bp:bgp-actions
                          +--rw bp:set-route-origin?
                          |                    bt:bgp-origin-attr-type
                          +--rw bp:set-local-pref?   uint32
                          +--rw bp:set-next-hop?     bgp-next-hop-type
                          +--rw bp:set-med?          bgp-set-med-type
                          +--rw bp:set-as-path-prepend
                          |  +--rw bp:repeat-n?   uint8
                          +--rw bp:set-community
                          |  +--rw bp:method?      enumeration
                          |  +--rw bp:options?
                          |  +--rw bp:inline
                          |  |  +--rw bp:communities*   union
                          |  +--rw bp:reference
                          |     +--rw bp:community-set-ref?
                          +--rw bp:set-ext-community
                             +--rw bp:method?      enumeration
                             +--rw bp:options?
                             +--rw bp:inline
                             |  +--rw bp:communities*   union
                             +--rw bp:reference
                                +--rw bp:ext-community-set-ref?

Appendix B.  Policy Examples

   Below, we show examples of XML-encoded configuration data using the
   routing policy and BGP models to illustrate both how policies are
   defined and how they can be applied.  Note that the XML
   [W3C.REC-xml11] has been simplified for readability.

   The following example shows how prefix set and tag set can be
   defined.  The policy condition is to match a prefix set and a tag
   set, and the action is to accept routes that match the condition.

     <config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
       <routing-policy
        xmlns="urn:ietf:params:xml:ns:yang:ietf-routing-policy">

           <defined-sets>
             <prefix-sets>
               <prefix-set>
                 <name>prefix-set-A</name>
                 <mode>ipv4</mode>
                 <prefixes>
                   <prefix-list>
                     <ip-prefix>192.0.2.0/24</ip-prefix>
                     <mask-length-lower>24</mask-length-lower>
                     <mask-length-upper>32</mask-length-upper>
                   </prefix-list>
                   <prefix-list>
                     <ip-prefix>198.51.100.0/24</ip-prefix>
                     <mask-length-lower>24</mask-length-lower>
                     <mask-length-upper>32</mask-length-upper>
                   </prefix-list>
                 </prefixes>
               </prefix-set>
               <prefix-set>
                 <name>prefix-set-B</name>
                 <mode>ipv6</mode>
                   <prefixes>
                   <prefix-list>
                     <ip-prefix>2001:DB8::/32</ip-prefix>
                     <mask-length-lower>32</mask-length-lower>
                     <mask-length-upper>64</mask-length-upper>
                   </prefix-list>
                 </prefixes>
               </prefix-set>
              </prefix-sets>
              <tag-sets>
               <tag-set>
                <name>cust-tag1</name>
                <tag-value>10</tag-value>
              </tag-set>
            </tag-sets>
          </defined-sets>

          <policy-definitions>
           <policy-definition>
             <name>export-tagged-BGP</name>
             <statements>
               <statement>
                 <name>term-0</name>
                 <conditions>
                   <match-prefix-set>
                     <prefix-set>prefix-set-A</prefix-set>
                   </match-prefix-set>
                   <match-tag-set>
                     <tag-set>cust-tag1</tag-set>
                   </match-tag-set>
                 </conditions>
                 <actions>
                   <policy-result>accept-route</policy-result>
                 </actions>
               </statement>
             </statements>
           </policy-definition>
         </policy-definitions>

         </routing-policy>
   </config>

   In the following example, all routes in the RIB that have been
   learned from OSPF advertisements corresponding to OSPF intra-area and
   inter-area route types should get advertised into IS-IS level 2
   advertisements.

   <config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <routing-policy
      xmlns="urn:ietf:params:xml:ns:yang:ietf-routing-policy">
      <policy-definitions>
       <policy-definition>
        <name>export-all-OSPF-prefixes-into-IS-IS-level-2</name>
         <statements>
          <statement>
            <name>term-0</name>
            <conditions>
              <match-route-type>
                <route-type>ospf-internal-type</route-type>
              </match-route-type>
            </conditions>
            <actions>
              <set-route-level>
                <route-level>isis-level-2</route-level>
              </set-route-level>
              <policy-result>accept-route</policy-result>
            </actions>
          </statement>
         </statements>
       </policy-definition>
      </policy-definitions>
     </routing-policy>
   </config>

Acknowledgements

   The routing policy module defined in this document is based on the
   OpenConfig route policy model.  The authors would like to thank
   OpenConfig for their contributions, especially those of Anees Shaikh,
   Rob Shakir, Kevin D'Souza, and Chris Chase.

   The authors are grateful for valuable contributions to this document
   and the associated models from Ebben Aires, Luyuan Fang, Josh George,
   Stephane Litkowski, Ina Minei, Carl Moberg, Eric Osborne, Steve
   Padgett, Juergen Schoenwaelder, Jim Uttaro, Russ White, and John
   Heasley.

   Thanks to Mahesh Jethanandani, John Scudder, Alvaro Retana, Chris
   Bowers, Tom Petch, and Kris Lambrechts for their reviews and
   comments.

Authors' Addresses

   Yingzhen Qu
   Futurewei
   2330 Central Expressway
   Santa Clara, CA 95050
   United States of America

   Email: yingzhen.qu@futurewei.com


   Jeff Tantsura
   Microsoft

   Email: jefftant.ietf@gmail.com


   Acee Lindem
   Cisco
   301 Midenhall Way
   Cary, NC 27513
   United States of America

   Email: acee@cisco.com


   Xufeng Liu
   Volta Networks

   Email: xufeng.liu.ietf@gmail.com