A YANG Data Model for Routing Policy
draft-ietf-rtgwg-policy-model-31

The information below is for an old version of the document that is already published as an RFC
Document Type RFC Internet-Draft (rtgwg WG)
Authors Yingzhen Qu  , Jeff Tantsura  , Acee Lindem  , Xufeng Liu 
Last updated 2021-10-11 (latest revision 2021-08-12)
Replaces draft-shaikh-rtgwg-policy-model
Stream Internet Engineering Task Force (IETF)
Formats plain text pdf htmlized bibtex
Reviews
Stream WG state Submitted to IESG for Publication
Document shepherd Chris Bowers
Shepherd write-up Show (last changed 2021-07-30)
IESG IESG state RFC 9067 (Proposed Standard)
Consensus Boilerplate Yes
Telechat date
Responsible AD Alvaro Retana
Send notices to Chris Bowers <chrisbowers.ietf@gmail.com>, aretana.ietf@gmail.com
IANA IANA review state IANA OK - Actions Needed
IANA action state RFC-Ed-Ack
IANA expert review state Expert Reviews OK
RFC Editor RFC Editor state AUTH48-DONE
Details
RTGWG                                                              Y. Qu
Internet-Draft                                                 Futurewei
Intended status: Standards Track                             J. Tantsura
Expires: February 13, 2022                                     Microsoft
                                                               A. Lindem
                                                                   Cisco
                                                                  X. Liu
                                                          Volta Networks
                                                         August 12, 2021

                  A YANG Data Model for Routing Policy
                    draft-ietf-rtgwg-policy-model-31

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 which can be extended for specific
   routing protocols using the YANG 'augment' mechanism.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 13, 2022.

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

Qu, et al.              Expires February 13, 2022               [Page 1]
Internet-Draft            Routing Policy Model               August 2021

   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Goals and approach  . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology and Notation  . . . . . . . . . . . . . . . . . .   3
     2.1.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Prefixes in Data Node Names . . . . . . . . . . . . . . .   4
   3.  Model overview  . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Route policy expression . . . . . . . . . . . . . . . . . . .   6
     4.1.  Defined sets for policy matching  . . . . . . . . . . . .   6
     4.2.  Policy conditions . . . . . . . . . . . . . . . . . . . .   7
     4.3.  Policy actions  . . . . . . . . . . . . . . . . . . . . .   8
     4.4.  Policy subroutines  . . . . . . . . . . . . . . . . . . .   9
   5.  Policy evaluation . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Applying routing policy . . . . . . . . . . . . . . . . . . .  10
   7.  YANG Module and Tree  . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Routing Policy Model Tree . . . . . . . . . . . . . . . .  11
     7.2.  Routing policy model  . . . . . . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  32
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  34
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     11.1.  Normative references . . . . . . . . . . . . . . . . . .  34
     11.2.  Informative references . . . . . . . . . . . . . . . . .  36
   Appendix A.  Routing protocol-specific policies . . . . . . . . .  36
   Appendix B.  Policy examples  . . . . . . . . . . . . . . . . . .  39
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  41

1.  Introduction

   This document describes a YANG [RFC7950] data model 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].

Qu, et al.              Expires February 13, 2022               [Page 2]
Internet-Draft            Routing Policy Model               August 2021

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 existing major 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]:

   o  client

Qu, et al.              Expires February 13, 2022               [Page 3]
Internet-Draft            Routing Policy Model               August 2021

   o  server

   o  configuration

   o  system state

   o  operational state

   o  intended configuration

   The following terms are defined in [RFC7950]:

   o  action

   o  augment

   o  container

   o  container with presence

   o  data model

   o  data node

   o  feature

   o  leaf

   o  list

   o  mandatory node

   o  module

   o  schema tree

   o  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, as long as it is clear from
   the context in which YANG module each name is defined.  Otherwise,

Qu, et al.              Expires February 13, 2022               [Page 4]
Internet-Draft            Routing Policy Model               August 2021

   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:

   o  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.

   o  A structure that allows routing protocol models to add protocol-
      specific policy conditions and actions though YANG augmentations
      is also provided.  There is a complete example of this for BGP
      [RFC4271] policies in the proposed vendor-neutral BGP data model
      [I-D.ietf-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.

   o  Finally, a reusable grouping is defined for attaching import and
      export rules in the context of routing configuration for different
      protocols, VRFs, etc.  This also enables creation of policy chains
      and expressing 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].

Qu, et al.              Expires February 13, 2022               [Page 5]
Internet-Draft            Routing Policy Model               August 2021

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
         +--ro match-modified-attributes?   boolean
         +--rw policy-definitions
            +--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 which have their own defined
   sets.  The defined sets include:

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

   o  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.

   o  tag set - Each tag set defines a set of generic tag values that
      can be used in matches for filtering routes.

   The model structure for defined sets is shown below.

Qu, et al.              Expires February 13, 2022               [Page 6]
Internet-Draft            Routing Policy Model               August 2021

       +--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.  The default action is to
   reject-route.

   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:

   o  ALL - match is true only if the given value matches all members of
      the set.

   o  ANY - match is true if the given value matches any member of the
      set.

   o  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.

Qu, et al.              Expires February 13, 2022               [Page 7]
Internet-Draft            Routing Policy Model               August 2021

   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*   identityref
                  |     +--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.

Qu, et al.              Expires February 13, 2022               [Page 8]
Internet-Draft            Routing Policy Model               August 2021

       +--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 and evaluation of the policy continues (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

Qu, et al.              Expires February 13, 2022               [Page 9]
Internet-Draft            Routing Policy Model               August 2021

   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., 2-3) is
   discouraged.  Also, implementations MUST validate 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 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.

Qu, et al.              Expires February 13, 2022              [Page 10]
Internet-Draft            Routing Policy Model               August 2021

   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 specifying
   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]

Qu, et al.              Expires February 13, 2022              [Page 11]
Internet-Draft            Routing Policy Model               August 2021

              +--rw name          string
              +--rw conditions
              |  +--rw call-policy?       -> ../../../../../..
              |                           /policy-definitions
              |                           /policy-definition/name
              |  +--rw source-protocol?      identityref
              |  +--rw match-interface
              |  |  +--rw interface?      -> /if:interfaces/interface
              |  |                        /name
              |  +--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*     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@2021-08-12.yang"
module ietf-routing-policy {

  yang-version "1.1";

Qu, et al.              Expires February 13, 2022              [Page 12]
Internet-Draft            Routing Policy Model               August 2021

  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 (NMDA Version)";
  }

  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>

     Editor:   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 model for routing policy
     configuration. It is a limited subset of all of the policy
     configuration parameters available in the variety of vendor

Qu, et al.              Expires February 13, 2022              [Page 13]
Internet-Draft            Routing Policy Model               August 2021

     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.

     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 XXXX;
     see the RFC itself for full legal notices.

     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.";

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

  revision "2021-08-12" {
    description
      "Initial revision.";
    reference
      "RFC XXXX: A YANG Data Model for Routing Policy Management.";
  }

  /* Identities */

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

  identity ospf-type-1-metric {
    base metric-type;
    description

Qu, et al.              Expires February 13, 2022              [Page 14]
Internet-Draft            Routing Policy Model               August 2021

      "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";

Qu, et al.              Expires February 13, 2022              [Page 15]
Internet-Draft            Routing Policy Model               August 2021

  }

  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.";

Qu, et al.              Expires February 13, 2022              [Page 16]
Internet-Draft            Routing Policy Model               August 2021

    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";
  }

Qu, et al.              Expires February 13, 2022              [Page 17]
Internet-Draft            Routing Policy Model               August 2021

  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

Qu, et al.              Expires February 13, 2022              [Page 18]
Internet-Draft            Routing Policy Model               August 2021

      "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.";

Qu, et al.              Expires February 13, 2022              [Page 19]
Internet-Draft            Routing Policy Model               August 2021

  }

  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.";
      }

Qu, et al.              Expires February 13, 2022              [Page 20]
Internet-Draft            Routing Policy Model               August 2021

      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

Qu, et al.              Expires February 13, 2022              [Page 21]
Internet-Draft            Routing Policy Model               August 2021

         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 {

Qu, et al.              Expires February 13, 2022              [Page 22]
Internet-Draft            Routing Policy Model               August 2021

        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 matching on
         'any' member of the set or 'invert' the match.
         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;

Qu, et al.              Expires February 13, 2022              [Page 23]
Internet-Draft            Routing Policy Model               August 2021

        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 which are matched as part of a policy.";
        list prefix-set {
          key "name mode";
          description
            "List of the defined prefix sets";

Qu, et al.              Expires February 13, 2022              [Page 24]
Internet-Draft            Routing Policy Model               August 2021

          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 that
               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;
            }
          }
        }
      }

Qu, et al.              Expires February 13, 2022              [Page 25]
Internet-Draft            Routing Policy Model               August 2021

      container neighbor-sets {
        description
          "Data definition for a list of IPv4 or IPv6
           neighbors which 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 which 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.";
          }
        }

Qu, et al.              Expires February 13, 2022              [Page 26]
Internet-Draft            Routing Policy Model               August 2021

      }
    }

    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.";

Qu, et al.              Expires February 13, 2022              [Page 27]
Internet-Draft            Routing Policy Model               August 2021

            }

            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.";
              }

              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 leafref {
                    path "/if:interfaces/if:interface/if:name";
                  }
                  description
                    "Reference to a base interface.";
                }
                description
                  "Container for interface match conditions";
              }

Qu, et al.              Expires February 13, 2022              [Page 28]
Internet-Draft            Routing Policy Model               August 2021

              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.";
              }

Qu, et al.              Expires February 13, 2022              [Page 29]
Internet-Draft            Routing Policy Model               August 2021

              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;
                default reject-route;
                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

Qu, et al.              Expires February 13, 2022              [Page 30]
Internet-Draft            Routing Policy Model               August 2021

                    "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', 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.";
              }
            }
          }
        }
      }
    }

Qu, et al.              Expires February 13, 2022              [Page 31]
Internet-Draft            Routing Policy Model               August 2021

  }
}
<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 NETCONF Access Control Model (NACM) [RFC8341] provides the means
   to restrict access for particular NETCONF or RESTCONF users to a pre-
   configured 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

Qu, et al.              Expires February 13, 2022              [Page 32]
Internet-Draft            Routing Policy Model               August 2021

      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 Denial-of-Service (DoS) attack.

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

      /routing-policy/policy-definitions/policy-definition /statements/
      -- Knowledge of these data nodes can be used to attack the local
      router with a Denial-of-Service (DoS) attack.  Additionally,
      policies and their attendant conditions and actions should be
      considered proprietary and disclosure could be used to ascertain
      partners, customers, and supplies.  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 models that reference routing
   policies are also susceptible to vulnerabilities relating the YANG
   data nodes specified above.

Qu, et al.              Expires February 13, 2022              [Page 33]
Internet-Draft            Routing Policy Model               August 2021

9.  IANA Considerations

   This document registers a URI in the IETF XML registry [RFC3688].
   Following the format in [RFC3688], the following registration is
   requested to be made:

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

   This document registers a YANG module in the YANG Module Names
   registry [RFC6020].

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

10.  Acknowledgements

   The routing policy module defined in this document is based on the
   OpenConfig route policy model.  The authors would like to thank to
   OpenConfig for their contributions, especially 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, Chris Bowers and Tom
   Petch for their reviews and comments.

11.  References

11.1.  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>.

Qu, et al.              Expires February 13, 2022              [Page 34]
Internet-Draft            Routing Policy Model               August 2021

   [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>.

Qu, et al.              Expires February 13, 2022              [Page 35]
Internet-Draft            Routing Policy Model               August 2021

   [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>.

11.2.  Informative references

   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
              YANG Model for Service Provider Networks", draft-ietf-idr-
              bgp-model-11 (work in progress), July 2021.

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 provides an illustration of how another data model
   can augment parts of this routing policy data model.  It uses

Qu, et al.              Expires February 13, 2022              [Page 36]
Internet-Draft            Routing Policy Model               August 2021

   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 [I-D.ietf-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 [I-D.ietf-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

Qu, et al.              Expires February 13, 2022              [Page 37]
Internet-Draft            Routing Policy Model               August 2021

              +--rw statement* [name]
                 +--rw name          string
                 +--rw conditions
                 |  +--rw call-policy?
                 |  +--rw source-protocol?          identityref
                 |  +--rw match-interface
                 |  |  +--rw interface?
                 |  +--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*   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

Qu, et al.              Expires February 13, 2022              [Page 38]
Internet-Draft            Routing Policy Model               August 2021

                       +--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 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>

Qu, et al.              Expires February 13, 2022              [Page 39]
Internet-Draft            Routing Policy Model               August 2021

                     <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>

Qu, et al.              Expires February 13, 2022              [Page 40]
Internet-Draft            Routing Policy Model               August 2021

   </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 ISIS 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-ISIS-level-2</name>
         <statements>
          <statement>
            <name>term-0</name>
            <conditions>
              <match-route-type>ospf-internal-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>

Authors' Addresses

   Yingzhen Qu
   Futurewei
   2330 Central Expressway
   Santa Clara  CA 95050
   USA

   Email: yingzhen.qu@futurewei.com

Qu, et al.              Expires February 13, 2022              [Page 41]
Internet-Draft            Routing Policy Model               August 2021

   Jeff Tantsura
   Microsoft

   Email: jefftant.ietf@gmail.com

   Acee Lindem
   Cisco
   301 Midenhall Way
   Cary, NC  27513
   US

   Email: acee@cisco.com

   Xufeng Liu
   Volta Networks

   Email: xufeng.liu.ietf@gmail.com

Qu, et al.              Expires February 13, 2022              [Page 42]