draft-ietf-rtgwg-policy-model-06.xml

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<rfc docName="draft-ietf-rtgwg-policy-model-06" ipr="trust200902" category="std">
<?rfc toc="yes"?>
  <front>
    <title abbrev="Routing Policy Model">A YANG Data Model for Routing Policy Management</title>
    <author fullname="Yingzhen Qu" initials="Y" surname="Qu">
      <organization>Huawei</organization>
      <address>
        <postal>
          <street>2330 Central Expressway</street>
          <city>Santa Clara</city>
          <code>CA 95050</code>
          <country>USA</country>
        </postal>
        <email>yingzhen.qu@huawei.com</email>
      </address>
    </author>
    <author fullname="Jeff Tantsura" initials="J" surname="Tantsura">
      <organization>Apstra</organization>
      <address>
        <email>jefftant.ietf@gmail.com</email>
      </address>
    </author>
    <author fullname="Acee Lindem" initials="A" surname="Lindem">
      <organization>Cisco</organization>
      <address>
        <postal>
          <street>301 Mindenhall Way</street>
          <city>Cary</city>
          <region>NC</region>
          <code>27513</code>
          <country>US</country>
        </postal>
        <email>acee@cisco.com</email>
      </address>
    </author>
    <author fullname="Xufeng Liu" initials="X" surname="Liu">
      <organization>Volta Networks</organization>
      <address>
        <email>xufeng.liu.ietf@gmail.com</email>
      </address>
    </author>

    <date/>

    <area>Routing</area>
    <workgroup>RTGWG</workgroup>

    <abstract>
      <t>This document defines a YANG data model for configuring and
        managing routing policies in a vendor-neutral way and based on
        actual operational practice. The model provides a generic policy
        framework which can be augmented with protocol-specific policy
        configuration.
      </t>
    </abstract>
  </front>

  <middle>
    <section title="Introduction" anchor="intro">
      <t>This document describes a <xref target="RFC6020">YANG</xref> <xref target="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, in order to allow operators to manage policy configuration in a consistent, intuitive way in heterogeneous environments with routers supplied by multiple vendors.
      </t>
      <t> The YANG modules in this document conform to the Network Management
      Datastore Architecture (NMDA) [RFC8342].</t>

      <section title = "Goals and approach" anchor="goals">
      <t>
      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 a number of operator
      networks.  Hence the focus is on enabling policy configuration
      capabilities and structure that are in wide use.
      </t>

      <t>
      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 an intuitive and
      straightforward way to express policy without sacrificing
      flexibility.  A side affect of this design decision is that
      legacy methods for expressing policies are not considered.  Such
      methods could be added as an augmentation to the model if
      needed.
      </t>

     <t>
      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.
      </t>
      </section>
    </section>

    <section title="Terminology and Notation">
      <t>
      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 <xref target="RFC2119"/> <xref target="RFC8174"/> 
      when, and only when, they appear in all capitals, as shown here.</t>
      <t>The following terms are defined in <xref target="RFC8342"/>:
        <list style="symbols">
          <t>client</t>
          <t>server</t>
          <t>configuration</t>
          <t>system state</t>
          <t>operational state</t>
          <t>intended configuration</t>
        </list>
      </t>

      <t>The following terms are defined in <xref target="RFC7950"/>:
        <list style="symbols">
          <t>action</t>
          <t>augment</t>
          <t>container</t>
          <t>container with presence</t>
          <t>data model</t>
          <t>data node</t>
          <t>feature</t>
          <t>leaf</t>
          <t>list</t>
          <t>mandatory node</t>
          <t>module</t>
          <t>schema tree</t>
          <t>RPC (Remote Procedure Call) operation</t>
        </list>
      </t>

      <section title="Tree Diagrams">
        <t>Tree diagrams used in this document follow the notation defined in  <xref target="RFC8340"/>.</t>
      </section>
      <section anchor="sec.prefixes" title="Prefixes in Data Node Names">
        <t>
        In this document, names of data nodes, actions, and other
        data model objects are often used without a prefix, as long as
        it is clear from the context in which YANG module each name is
        defined. Otherwise, names are prefixed using the standard prefix
        associated with the corresponding YANG module, as shown in <xref target="tab.prefixes"/>.
        </t>

        <texttable anchor="tab.prefixes" title="Prefixes and Corresponding YANG Modules">
          <ttcol>Prefix</ttcol>
          <ttcol>YANG module</ttcol>
          <ttcol>Reference</ttcol>
          <c>if</c><c>ietf-interfaces</c><c><xref target="RFC8343"/></c>
          <c>rt</c><c>ietf-routing</c><c><xref target="RFC8349"/></c>
          <c>yang</c><c>ietf-yang-types</c><c><xref target="RFC6991"/></c>
          <c>inet</c><c>ietf-inet-types</c><c><xref target="RFC6991"/></c>
          <c>if-cmn</c><c>ietf-interfaces-common</c><c><xref target="I-D.ietf-netmod-intf-ext-yang"/></c>
        </texttable>
      </section>
    </section>

    <section title="Model overview" anchor="overview">
      <t>
      The routing policy module has three main parts:
      </t>
      <t>
        <list style="symbols">
          <t>
          A generic framework to express policies as sets of related
          conditions and actions. This includes match sets and actions
          that are useful across many routing protocols.
          </t>
          <t>
          A structure that allows routing protocol models to add
          protocol-specific policy conditions and actions though
          YANG augmentations.  There is a complete example of this
          for <xref target="RFC4271">BGP</xref> policies in the proposed vendor-neutral
          <xref target="I-D.ietf-idr-bgp-model">BGP data model</xref>.
          </t>
          <t>
          A reusable grouping 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.
          </t>
        </list>
      </t>
      <t>
        The module makes use of the standard Internet types,
        such as IP addresses, autonomous system numbers, etc.,
        defined in <xref target="RFC6991">RFC 6991</xref>.
      </t>
    </section>

    <section title="Route policy expression" anchor="expression">
      <t>
      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 effect multiple changes to
      route attributes, or indicate a final disposition of accepting
      or rejecting the route.  This structure is shown below.
      </t>

      <figure>
        <artwork>
   +--rw routing-policy
      +--rw policy-definitions
         +--rw policy-definition* [name]
            +--rw name          string
            +--rw statements
               +--rw statement* [name]
                  +--rw name          string
                  +--rw conditions
                  |     ...
                  +--rw actions
                        ...
        </artwork>
      </figure>

      <section title="Defined sets for policy matching" anchor="sets">
        <t>
        The models provides a set 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
        supported defined sets include:
        </t>
        <t>
          <list style="symbols">
          <t>
            prefix sets - define a set of IP prefixes, each with an
            associated CIDR netmask range (or exact length)
          </t>
          <t>
            neighbor sets - define a set of neighboring nodes by their
            IP addresses. These sets are used for selecting routes based on the
            neighbors advertising the routes.
          </t>
          <t>
            tag set - define a set of generic tag values that can be used
            in matches for filtering routes
          </t>
          </list>
        </t>
        <t>
          The model structure for defined sets is shown below.
        </t>

        <figure>
          <artwork>
    +--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 masklength-lower 
       |  |                            masklength-upper]
       |  |           +--rw ip-prefix           inet:ip-prefix
       |  |           +--rw masklength-lower    uint8
       |  |           +--rw masklength-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

          </artwork>
        </figure>
      </section>


      <section title="Policy conditions" anchor="conditions">
        <t>
        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.
        </t>

        <t>
        Match conditions may be further modified using the
        match-set-options configuration which allows operators to
        change the behavior of a match. Three options are supported:
        </t>
        <t>
          <list style="symbols">
            <t>ALL - match is true only if the given value matches
              all members of the set.
            </t>
            <t>ANY - match is true if the given value matches any
              member of the set.
            </t>
            <t>INVERT - match is true if the given value does not
              match any member of the given set.
            </t>
          </list>
        </t>
        <t>
        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.
        </t>

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

        <t>
        While most policy conditions will be added by individual
        routing protocol models via augmentation, this routing policy
        model includes several generic match conditions and also 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.
        </t>

        <figure>
          <artwork>
+--rw routing-policy
  +--rw policy-definitions
      +--rw policy-definition* [name]
         +--rw name          string
         +--rw statements
            +--rw statement* [name]
               +--rw conditions
               |  +--rw call-policy?
               |  +--rw install-protocol-eq?
               |  +--rw match-interface
               |  |  +--rw interface?
               |  |  +--rw subinterface?
               |  +--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? 
        </artwork>
        </figure>
      </section>

      <section title="Policy actions" anchor="actions">

        <t>
        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.
        </t>

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

        <figure>
          <artwork>
    +--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?       uint32
                    +--rw set-preference?   uint16
          </artwork>
        </figure>

      </section>

      <section title="Policy subroutines" anchor="subroutines">

        <t>
        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 <xref target="evaluation"></xref>).  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 chain
        is reached, the default route disposition action is returned (i.e.,
        boolean false for reject-route unless an alternate default action
        is specified for the chain). Consequently, a subroutine cannot
        explicitly accept or reject a route. Rather it merely provides
        an indication that 'call-policy' condition returns boolean true
        or false indicating whether or not the condition matches. Route 
        acceptance or rejection is solely determined by the top-level
        policy.
        </t>

      	<t>
      	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,
        some major 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., 2-3)
        should be discouraged.
        </t>

      </section>

    </section>

    <section title="Policy evaluation" anchor="evaluation">

      <t>
      Evaluation of each policy definition proceeds by evaluating its
      corresponding individual policy statements in order.  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 definitions in the chain are evaluated.
      </t>

      <t>
      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).
      </t>

      <t>
      Note that the route's pre-policy attributes are always used for
      testing policy statement conditions. In other words, if actions modify
      the policy application specific attributes, those modifications are
      not used for policy statement conditions.
      </t>

    </section>

    <section title="Applying routing policy" anchor="usage">

      <t>
      Routing policy is applied by defining and attaching policy chains
      in various routing contexts.  Policy chains are sequences of
      policy definitions (described in <xref target="expression">
      </xref>) that have an associated direction (import or export)
      with respect to the routing context in which they are defined.
      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.
      </t>

      <figure>
        <artwork>
      +--rw apply-policy
      |  +--rw import-policy*
      |  +--rw default-import-policy?   default-policy-type
      |  +--rw export-policy*
      |  +--rw default-export-policy?   default-policy-type
        </artwork>
      </figure>

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

    </section>

    <section title="Routing protocol-specific policies" anchor="augment">

      <t>
      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.
      </t>

      <t>
      An example of this is shown below, in which the BGP configuration
      model in <xref target="I-D.ietf-idr-bgp-model"></xref>
      adds new defined sets to match on community values or AS paths.
      The model similarly augments BGP-specific conditions and actions
      in the corresponding sections of the routing policy model.
      </t>


      <figure>
        <artwork>
+--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 masklength-lower 
   |  |                            masklength-upper]
   |  |           +--rw ip-prefix           inet:ip-prefix
   |  |           +--rw masklength-lower    uint8
   |  |           +--rw masklength-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 bgp-pol:bgp-defined-sets
   |     +--rw bgp-pol:community-sets
   |     |  +--rw bgp-pol:community-set* [community-set-name]
   |     |     +--rw bgp-pol:community-set-name    string
   |     |     +--rw bgp-pol:community-member*     union
   |     +--rw bgp-pol:ext-community-sets
   |     |  +--rw bgp-pol:ext-community-set* [ext-community-set-name]
   |     |     +--rw bgp-pol:ext-community-set-name    string
   |     |     +--rw bgp-pol:ext-community-member*     union
   |     +--rw bgp-pol:as-path-sets
   |        +--rw bgp-pol:as-path-set* [as-path-set-name]
   |           +--rw bgp-pol:as-path-set-name      string
   |           +--rw bgp-pol:as-path-set-member*   string
   +--rw policy-definitions
      +--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?      
               |  |  +--rw subinterface?   
               |  +--rw match-prefix-set
               |  |  +--rw prefix-set?          
               |  |  +--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 bgp-pol:bgp-conditions
               |     +--rw bgp-pol:med-eq?      uint32
               |     +--rw bgp-pol:origin-eq?   
               |           bgp-types:bgp-origin-attr-type
               |     +--rw bgp-pol:next-hop-in* 
               |           inet:ip-address-no-zone
               |     +--rw bgp-pol:afi-safi-in*   identityref
               |     +--rw bgp-pol:local-pref-eq? uint32
               |     +--rw bgp-pol:route-type?    enumeration
               |     +--rw bgp-pol:community-count
               |     +--rw bgp-pol:as-path-length
               |     +--rw bgp-pol:match-community-set
               |     |  +--rw bgp-pol:community-set?       
               |     |  +--rw bgp-pol:match-set-options?   
               |              match-set-options-type
               |     +--rw bgp-pol:match-ext-community-set
               |     |  +--rw bgp-pol:ext-community-set?   
               |     |  +--rw bgp-pol:match-set-options?   
               |     |        match-set-options-type
               |     +--rw bgp-pol:match-as-path-set
               |        +--rw bgp-pol:as-path-set?         
               |        +--rw bgp-pol:match-set-options?   
               |              match-set-options-type
               +--rw actions
                  +--rw policy-result?         policy-result-type
                  +--rw set-metric?            uint32
                  +--rw set-preference?        uint16
                  +--rw bgp-pol:bgp-actions
                     +--rw bgp-pol:set-route-origin?      
                           bgp-types:bgp-origin-attr-type
                     +--rw bgp-pol:set-local-pref?        uint32
                     +--rw bgp-pol:set-next-hop?   bgp-next-hop-type
                     +--rw bgp-pol:set-med?        bgp-set-med-type
                     +--rw bgp-pol:set-as-path-prepend
                     |  +--rw bgp-pol:repeat-n?   uint8
                     +--rw bgp-pol:set-community
                     |  +--rw bgp-pol:method?      enumeration
                     |  +--rw bgp-pol:options?     
                              bgp-set-community-option-type
                     |  +--rw bgp-pol:inline
                     |  |  +--rw bgp-pol:communities*   union
                     |  +--rw bgp-pol:reference
                     |     +--rw bgp-pol:community-set-ref?   
                     +--rw bgp-pol:set-ext-community
                        +--rw bgp-pol:method?       enumeration
                        +--rw bgp-pol:options?      
                              bgp-set-community-option-type
                        +--rw bgp-pol:inline
                        |  +--rw bgp-pol:communities*   union
                        +--rw bgp-pol:reference
                           +--rw bgp-pol:ext-community-set-ref?   
        </artwork>
      </figure>

    </section>

    <section title="Security Considerations">

      <t>Routing policy configuration has a significant impact on network operations,
      and, as such, any related model carries potential security risks.
      </t>

      <t>YANG data models are generally designed to be used with the
      NETCONF protocol over an SSH transport.  This provides an
      authenticated and secure channel over which to transfer
      configuration and operational data.  Note that use of
      alternate transport or data encoding (e.g., JSON over HTTPS)
      would require similar mechanisms for authenticating and
      securing access to configuration data.
      </t>

      <t>Most of the data elements in the policy model could be
      considered sensitive from a security standpoint.  Unauthorized
      access or invalid data could cause major disruption.
      </t>

    </section>

    <section title="IANA Considerations">

      <t>This YANG data model and the component modules currently use
      a temporary ad-hoc namespace.  If and when it is placed on redirected for
      the standards track, an appropriate namespace URI will be
      registered in the <xref target="RFC3688">IETF XML Registry"</xref>.
      The routing policy YANG modules will be registered in the
      "YANG Module Names" registry [RFC6020].
      </t>
    </section>

    <section title="YANG modules" anchor="models">

      <t>The routing policy model is described by the YANG modules in the
      sections below.
      </t>

      <section title="Routing policy model">
	<figure>
	<artwork><![CDATA[
<CODE BEGINS> file "ietf-routing-policy@2019-03-06.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";
  }

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

  import ietf-interfaces {
    prefix "if";
  }

  import ietf-routing {
    prefix "rt";
  }

  import ietf-interfaces-common {
    prefix if-cmn;
  }

  import ietf-if-l3-vlan {
    prefix "if-l3-vlan";
  }


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


     Editor:   Yingzhen Qu
               <mailto:yingzhen.qu@huawei.com>
               Jeff Tantsura
               <mailto:jefftant.ietf@gmail.com>
               Acee Lindem
               <mailto:acee@cisco.com>
               Xufeng Liu
               <mailto:xufeng_liu@jabil.com>
               Anees Shaikh
               <mailto:aashaikh@google.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
     implementations, but supports widely used constructs for
     managing how routes are imported, exported, and modified across
     different routing protocols.  This module is intended to be
     used in conjunction with routing protocol configuration modules
     (e.g., BGP) defined in other models.

     Route policy expression:

     Policies are expressed as a set of top-level policy
     definitions, each of which consists of a sequence of policy
     statements. Policy statements consist of simple
     condition-action tuples. Conditions may include mutiple match
     or comparison operations, and similarly actions may be
     multitude of changes to route attributes or a final disposition
     of accepting or rejecting the route.

     Route policy evaluation:

     Policy definitions are referenced in routing protocol
     configurations using import and export configuration
     statements. The arguments are members of an ordered list of
     named policy definitions which comprise a policy chain, and
     optionally, an explicit default policy action (i.e., reject
     or accept).

     Evaluation of each policy definition proceeds by evaluating its
     corresponding individual policy statements in order.  When a
     condition statement in a policy statement is satisfied, the
     corresponding action statement is executed.  If the action
     statement has either accept-route or reject-route actions,
     policy evaluation of the current policy definition stops, and
     no further policy definitions in the chain are evaluated.

     If the condition is 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).

     Policy 'subroutines' (or nested policies) are supported by
     allowing policy statement conditions to reference another
     policy definition which applies conditions and actions from
     the referenced policy before returning to the calling policy
     statement and resuming evaluation.  If the called policy
     results in an accept-route (either explicit or by default),
     then the subroutine returns an effective true value to the
     calling policy.  Similarly, a reject-route action returns
     false.  If the subroutine returns true, the calling policy
     continues to evaluate the remaining conditions (using a
     modified route if the subroutine performed any changes to the
     route).";


  revision "2019-03-06" {
    description
      "Initial revision.";
    reference
     "RFC XXXX: Routing Policy Configuration Model for Service
      Provider Networks";
  }


  // typedef statements

  typedef default-policy-type {
    // this typedef retained for name compatibiity with default
    // import and export policy
    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";
  }

  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 2178 - 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";
  }


  // grouping statements

  grouping prefix-set {
    description
      "Configuration data for prefix sets used in policy
       definitions.";

    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";
        }
        enum mixed {
          description
            "Prefix set contains mixed IPv4 and IPv6 prefixes";
        }
      }
      description
        "Indicates the mode of the prefix set, in terms of which
         address families (IPv4, IPv6, or both) are present.  The
         mode provides a hint, but the device must validate that all
         prefixes are of the indicated type, and is expected to
         reject the configuration if there is a discrepancy.  The
         MIXED mode may not be supported on devices that require
         prefix sets to be of only one address family.";
    }

  }

  grouping prefix-set-top {
    description
      "Top-level data definitions for a list of IPv4 or IPv6
       prefixes which are matched as part of a policy";

    container prefix-sets {
      description
        "Enclosing container ";

      list prefix-set {
        key "name";
        description
          "List of the defined prefix sets";

        uses prefix-set;

        uses prefix-top;
      }
    }
  }

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

    leaf ip-prefix {
      type inet:ip-prefix;
      mandatory true;
      description
        "The prefix member in CIDR notation -- while the
         prefix may be either IPv4 or IPv6, most
         implementations require all members of the prefix set
         to be the same address family.  Mixing address types in
         the same prefix set is likely to cause an error.";
    }

    leaf masklength-lower {
      type uint8;
      description
        "Masklength range lower bound.";
    }
    leaf masklength-upper {
      type uint8 {
        range "1..128";
      }
      must "../masklength-upper >= ../masklength-lower" {
        error-message "The upper bound should not be less"
                    + "than lower bound.";
      }
      description
        "Masklength range upper bound.

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

         Example: 10.3.192.0/21 through 10.3.192.0/24 would be
         expressed as prefix: 10.3.192.0/21,
                      masklength-lower=21,
                      masklength-upper=24

         Example: 10.3.192.0/21 (an exact match) would be
         expressed as prefix: 10.3.192.0/21,
                      masklength-lower=21,
                      masklength-upper=21";
    }
  }

  grouping prefix-top {
    description
      "Top-level grouping for prefixes in a prefix list";

    container prefixes {
      description
        "Enclosing container for the list of prefixes in a policy
         prefix list";

      list prefix-list {
        key "ip-prefix masklength-lower masklength-upper";
        description
          "List of prefixes in the prefix set";

        uses prefix;
      }
    }
  }

  grouping neighbor-set {
    description
      "This grouping provides neighbor set definitions";

    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";
    }
  }

  grouping neighbor-set-top {
    description
      "Top-level data definition for a list of IPv4 or IPv6
       neighbors which can be matched in a routing policy";

    container neighbor-sets {
      description
        "Enclosing container for the list of neighbor set
         definitions";

      list neighbor-set {
        key "name";
        description
          "List of defined neighbor sets for use in policies.";

        uses neighbor-set;
      }
    }
  }

  grouping tag-set {
    description
      "This grouping provides 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";
    }
  }

  grouping tag-set-top {
    description
      "Top-level data definitions for a list of tags which can
       be matched in policies";

    container tag-sets {
      description
        "Enclosing container for the list of tag sets.";

      list tag-set {
        key "name";
        description
          "List of tag set definitions.";

        uses tag-set;

      }
    }
  }


  grouping match-set-options-group {
    description
      "Grouping containing options relating to how a particular set
       should 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 matching on ANY
         member of the set or inverting the match.  Matching on ALL
         is not supported";
    }
  }



  grouping match-interface-condition {
    description
      "This grouping provides interface match condition";

    container match-interface {
      leaf interface {
        type leafref {
          path "/if:interfaces/if:interface/if:name";
        }
        description
          "Reference to a base interface.  If a reference to a
           subinterface is required, this leaf must be specified
           to indicate the base interface.";
      }
      leaf subinterface {
        type leafref {
          path "/if:interfaces/if:interface/if-cmn:encapsulation"
             + "/if-l3-vlan:dot1q-vlan"
             + "/if-l3-vlan:outer-tag/if-l3-vlan:vlan-id";
        }
        description
          "Reference to a subinterface -- this requires the base
           interface to be specified using the interface leaf in
           this container.  If only a reference to a base interface
           is requuired, this leaf should not be set.";
      }

      description
        "Container for interface match conditions";
    }
  }

  grouping prefix-set-condition {
    description
      "This grouping provides prefix-set 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";
    }
  }

  grouping neighbor-set-condition {
    description
      "This grouping provides neighbor-set conditions";

    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 according to the logic
         defined in the match-set-options-leaf";
    }
  }

  grouping tag-set-condition {
    description
      "This grouping provides tag-set conditions";

    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-restricted-group;

      description
        "Match a referenced tag set according to the logic defined
         in the match-options-set leaf";
    }
  }

  grouping generic-conditions {
    description "Condition statement definitions for checking
       membership in a generic defined set";

    uses match-interface-condition;
    uses prefix-set-condition;
    uses neighbor-set-condition;
    uses tag-set-condition;

  }

  grouping policy-conditions {
    description
      "Data for general policy conditions, i.e., those
       not related to match-sets";

      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 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 and implementation dependent";
      }

      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";
      }
  }

  grouping policy-conditions-top {
    description
      "Top-level grouping for policy conditions";

    container conditions {
      description
        "Condition statements for the current policy statement";

      uses policy-conditions;

      uses generic-conditions;
    }
  }

  grouping policy-statements {
    description
      "Data for policy statements";

    leaf name {
      type string;
      description
        "Name of the policy statement";
    }
  }


  grouping policy-actions {
    description
      "Top-level grouping for policy actions";

    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.";
      }
      leaf set-metric {
        type uint32;
        description
          "Set a new metric for the route.";
      }
      leaf set-preference {
        type uint16;
        description
          "Set a new preference for the route.";
      }
    }
  }

  grouping policy-statements-top {
    description
      "Top-level grouping for the policy statements list";

    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 (see the description of policy
           evaluation at the top of this module.";

        uses policy-statements;

        uses policy-conditions-top;
        uses policy-actions;
      }
    }
  }


  grouping policy-definitions {
    description
      "This grouping provides policy definitions";

    leaf name {
      type string;
      description
        "Name of the top-level policy definition -- this name
        is used in references to the current policy";
    }
  }

  grouping apply-policy-import {
    description
      "Grouping for applying import policies";

    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 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.";
    }

  }

  grouping apply-policy-export {
    description
      "Grouping for applying export policies";

    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
         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.";
    }
  }


  grouping apply-policy {
    description
      "Configuration data for routing policies";

    uses apply-policy-import;
    uses apply-policy-export;

    container apply-policy-state {
      description
        "Operational state associated with routing policy";

      //TODO: identify additional state data beyond the intended
      //policy configuration.
    }

  }


  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.";

      uses apply-policy;

    }
  }

  container routing-policy {
    description
      "Top-level container for all routing policy";

    container defined-sets {
      description
        "Predefined sets of attributes used in policy match
         statements";

      uses prefix-set-top;
      uses neighbor-set-top;
      uses tag-set-top;
    }

    container policy-definitions {
      description
        "Enclosing container for the list of top-level policy
         definitions";

      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.";

        uses policy-definitions;

        uses policy-statements-top;
      }
    }
  }
}
<CODE ENDS>
 ]]>
        </artwork>
        </figure>
      </section>


    </section>

    <section title="Policy examples" anchor="examples">

      <t>
      Below we show an example of XML-encoded configuration data using
      the routing policy and BGP models to illustrate both how policies
      are defined, and also how they can be applied.  Note that the XML
      has been simplified for readability.
      </t>

      <figure>
        <artwork><![CDATA[
<?yfile include="file:///tmp/routing-policy-example-draft.xml"?>
 ]]>
        </artwork>
      </figure>

    </section>

  </middle>

  <back>
    <references title="Normative references">
      &RFC2119;
      &RFC3688;
      &RFC4271;
      &RFC6020;
      &RFC6991;
      &RFC7950;
      &RFC8174;
      &RFC8340;
      &RFC8342;
      &RFC8343;
      &RFC8349;
      <?rfc include="reference.I-D.ietf-netmod-intf-ext-yang"?>
      <?rfc include="reference.I-D.ietf-netmod-sub-intf-vlan-model"?>
    </references>

    <references title="Informative references">
      <?rfc include="http://xml2rfc.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-idr-bgp-model.xml"?>
    </references>

    <section title="Acknowledgements">
      <t>The routing policy module defined in this draft 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.
    </t>
      <t>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.
      </t>

    </section>
  </back>
</rfc>