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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" submissionType="IETF"
     category="std" consensus="yes" docName="draft-ietf-softwire-yang-16" ipr="trust200902"> number="8676" ipr="trust200902"
     obsoletes="" updates="" xml:lang="en" tocInclude="true" symRefs="true"
     sortRefs="true" version="3">
  <!-- xml2rfc v2v3 conversion 2.34.0 -->
  <front>
    <title abbrev="YANG Modules for A+P Softwires">YANG Modules for
    IPv4-in-IPv6 Address plus Port (A+P) (A&wj;+P) Softwires</title>
    <seriesInfo name="RFC" value="8676"/>
    <author fullname="Ian Farrer" initials="I." role="editor" surname="Farrer">
      <organization>Deutsche Telekom AG</organization>
      <address>
        <postal>
          <street>CTO-ATI, Landgrabenweg 151</street>
          <city>Bonn</city>
          <region>NRW</region>
          <code>53227</code>
          <country>Germany</country>
        </postal>
        <email>ian.farrer@telekom.de</email>
      </address>
    </author>
    <author fullname="Mohamed Boucadair" initials="M." role="editor" surname="Boucadair">
      <organization>Orange</organization>
      <address>
        <postal>
          <street></street>
          <street/>
          <city>Rennes</city>

          <region></region>
          <region/>
          <code>35000</code>
          <country>France</country>
        </postal>
        <email>mohamed.boucadair@orange.com</email>
      </address>
    </author>
    <date day="29" month="January" year="2019" />

    <workgroup>Softwire month="November" year="2019"/>
    <workgroup>Softwires Working Group</workgroup>
    <keyword>A+P</keyword>
    <keyword>address sharing</keyword>
    <keyword>port set</keyword>
    <keyword>Port range</keyword>
    <keyword>IPv4 service continuity</keyword>
    <keyword>NETCONF</keyword>
    <keyword>RESTCONF</keyword>
    <keyword>Programmability</keyword>
    <keyword>Dynamic provisioning</keyword>
    <keyword>automation</keyword>
    <keyword>IPv6</keyword>
    <abstract>
      <t>This document defines YANG modules for the configuration and
      operation of IPv4-in-IPv6 softwire Border Relays and Customer Premises
      Equipment for the Lightweight 4over6, Mapping of Address and Port with
      Encapsulation (MAP-E), and Mapping of Address and Port using Translation
      (MAP-T) softwire mechanisms.</t>
    </abstract>

    <note title="Editorial Note (To be removed by RFC Editor)">
      <t>Please update these statements within this document with the RFC
      number to be assigned to this document:<list style="symbols">
          <t>"This version of this YANG module is part of RFC XXXX;"</t>

          <t>"RFC XXXX: YANG Modules for IPv4-in-IPv6 Address plus Port
          Softwires";</t>

          <t>"reference: RFC XXXX"</t>
        </list>Please update the "revision" date of the YANG modules.</t>
    </note>
  </front>

  <middle>
    <section anchor="introduction" title="Introduction"> numbered="true" toc="default">
      <name>Introduction</name>
      <t>The IETF Softwire working group Working Group has developed several IPv4-in-IPv6
      softwire mechanisms to address various deployment contexts and
      constraints. As a companion to the architectural specification
      documents, this document focuses on the provisioning of address Address plus
      port
      Port (A+P) softwire functional elements: Border Routers (BRs) and
      Customer Edge (CE) (called "Customer Premises Equipment (CEs, a.k.a., CPE). (CPE)"
      in <xref target="RFC7596"/>). The softwire mechanisms
      covered in this document are Lightweight 4 over 6 4over6 (lw4o6) <xref
      target="RFC7596"></xref>, target="RFC7596" format="default"/>, Mapping of Address and Port with Encapsulation
      (MAP-E) <xref target="RFC7597"></xref>, target="RFC7597" format="default"/>, and Mapping of Address and Port
      using Translation (MAP-T) <xref target="RFC7599"></xref>.</t> target="RFC7599" format="default"/>.</t>
      <t>This document focuses on A+P mechanisms <xref
      target="RFC6346"></xref>; target="RFC6346" format="default"/>; the reader can refer to <xref
      target="RFC8513"></xref> target="RFC8513" format="default"/> for a YANG module for DS-Lite Dual-Stack Lite (DS-Lite) <xref
      target="RFC6333"></xref>.</t> target="RFC6333" format="default"/>.</t>
      <t>This document defines YANG modules <xref target="RFC7950"></xref> target="RFC7950" format="default"/>
      that can be used to configure and manage A+P softwire elements using the
      NETCONF <xref target="RFC6241"></xref>, target="RFC6241" format="default"/> or RESTCONF <xref
      target="RFC8040"></xref> target="RFC8040" format="default"/> protocols for:</t>

      <t><list hangIndent="22" style="symbols">
          <t>Configuration</t>

          <t>Operational State</t>

          <t>Notifications</t>
        </list></t>
      <ul spacing="normal">
        <li>Configuration</li>
        <li>Operational State</li>
        <li>Notifications</li>
      </ul>
    </section>
    <section anchor="terminology" title="Terminology"> numbered="true" toc="default">
      <name>Terminology</name>
      <t>The reader should be familiar with the concepts and terms defined in
      <xref target="RFC7596"></xref>, target="RFC7596" format="default"/>, <xref target="RFC7597"></xref>, target="RFC7597" format="default"/>, <xref
      target="RFC7599"></xref>, target="RFC7599" format="default"/>, and the YANG data modelling modeling language defined
      in <xref target="RFC7950"></xref>.</t> target="RFC7950" format="default"/>.</t>
      <t>The YANG modules in this document adopt the Network Management
      Datastore Architecture (NMDA) <xref target="RFC8342"></xref>. target="RFC8342" format="default"/>. The
      meanings of the symbols used in tree diagrams are defined in <xref
      target="RFC8340"></xref>.</t> target="RFC8340" format="default"/>.</t>
      <t>The document uses the abbrieviation abbreviation 'BR' as a general term for
      softwire tunnel concentrators, including both MAP Border Routers <xref
      target="RFC7597"></xref> target="RFC7597" format="default"/> and Lightweight 4over6 lWAFTRs lwAFTRs <xref
      target="RFC7596"></xref>.</t> target="RFC7596" format="default"/>.</t>
      <t>For brevity, "algorithm" is used to refer to the "mapping algorithm"
      defined in <xref target="RFC7597"></xref>.</t> target="RFC7597" format="default"/>.</t>
      <t>A network element may support one or multiple instances of a softwire
      mechanism; each of these instances (i.e., binding instances, MAP-E
      instances, or MAP-T instances) may have its own configuration and
      parameters. The term 'algo-instance' is used to denote both MAP-E and
      MAP-T instances.</t>
    </section>
    <section anchor="overview" title="Overview numbered="true" toc="default">
      <name>Overview of the Modules"> Modules</name>
      <section title="Overall Structure"> numbered="true" toc="default">
        <name>Overall Structure</name>
        <t>The document defines the following two YANG modules for the
        configuration and monitoring of softwire functional elements:</t>

        <t><list hangIndent="22" style="hanging">
            <t hangText="ietf-softwire-ce">Provides
<ul empty="true"><li>
        <dl newline="true" spacing="normal" indent="3">
          <dt>ietf-softwire-ce</dt>
          <dd>Provides configuration and
            monitoring for softwire CE element. This module is defined as
            augments to the interface YANG module <xref
            target="RFC8343"></xref>.</t>

            <t hangText="ietf-softwire-br">Provides target="RFC8343" format="default"/>.</dd>
          <dt>ietf-softwire-br</dt>
          <dd>Provides configuration and
            monitoring for softwire BR element.</t>
          </list></t> element.</dd>
        </dl>
      </li>
</ul>
        <t>In addition, the following module is defined:</t>

        <t><list hangIndent="22" style="hanging">
            <t hangText="ietf-softwire-common">Contains
<ul empty="true"><li>
        <dl newline="true" spacing="normal" indent="3">
          <dt>ietf-softwire-common</dt>
          <dd>Contains groups of common
            functions that are imported into the CE and BR modules.</t>
          </list></t> modules.</dd>
        </dl>
      </li>
</ul>
        <t>This approach has been taken so that the various modules can be
        easily extended to support additional softwire mechanisms, if
        required.</t>
        <t>Within the BR and CE modules, the YANG "feature" statement is used
        to distinguish which of the different softwire mechanism(s) is
        relevant for a specific element's configuration. For each module, a
        choice statement 'ce-type' is included for either 'binding' or
        'algorithm'. 'Binding' is used for configuring Lightweight 4over6,
        whereas 'algorithm' is used for configuring MAP-T or MAP-E.</t>
        <t>In the 'algo-instances' container, a choice statement 'data-plane'
        is included to specify MAP-E (encapsulation) or MAP-T (translation).
        <xref target="table_s46_mechanism_choices"></xref> target="table_s46_mechanism_choices" format="default"/> shows how these
        choices are used to indicate the desired softwire mechanism:</t>

        <texttable
        <table anchor="table_s46_mechanism_choices"
                   title="Softwire align="center">
          <name>Softwire Mechanism Choice Statement Enumeration">
          <ttcol Statement&nbsp;Enumeration</name>
          <thead>
            <tr>
              <th align="center">S46 Mechanism</ttcol>

          <ttcol align="center">ce-type?</ttcol>

          <ttcol align="center">data-plane?</ttcol>

          <c>Lightweight 4over6</c>

          <c>binding</c>

          <c>n/a</c>

          <c>MAP-E</c>

          <c>algorithm</c>

          <c>encapsulation</c>

          <c>MAP-T</c>

          <c>algorithm</c>

          <c>translation</c>
        </texttable> Mechanism</th>
              <th align="center">ce-type?</th>
              <th align="center">data-plane?</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td align="center">Lightweight 4over6</td>
              <td align="center">binding</td>
              <td align="center">n/a</td>
            </tr>
            <tr>
              <td align="center">MAP-E</td>
              <td align="center">algorithm</td>
              <td align="center">encapsulation</td>
            </tr>
            <tr>
              <td align="center">MAP-T</td>
              <td align="center">algorithm</td>
              <td align="center">translation</td>
            </tr>
          </tbody>
        </table>
        <t>NETCONF notifications are also included.<list style="empty">
            <t>Note: Earlier included.</t>
<aside><t>Earlier draft versions of this specification combined the
            softwire mechanisms by their associated technologies rather than
            their function in the architecture. As the document was revised,
            it became apparent that dividing the modules by their role in the
            architecture (CE or BR) was a better approach as this follows the
            intended function and existing implementation approaches more
            closely.</t>
          </list></t>
</aside>
      </section>

      <section title="Additional Components Configuration"> numbered="true" toc="default">
        <name>Configuration for Additional Components</name>
        <t>The softwire modules only aim to provide configuration relevant for
        softwires. In order to fully provision a CE element, the following may
        also be necessary:</t>

        <t><list style="symbols">
            <t>IPv6
        <ul spacing="normal">
          <li>IPv6 forwarding and routing configuration, enabling to enable the CE to
            obtain one or more IPv6 prefixes for softwire usage. A YANG module
            for routing management is described in <xref
            target="RFC8349"></xref>.</t>

            <t>IPv4 target="RFC8349" format="default"/>.</li>
          <li>IPv4 routing configuration, to add one or more IPv4 destination
            prefix(es) reachable via the configured softwire. A YANG module
            for routing management is described in <xref
            target="RFC8349"></xref>.</t>

            <t>Stateful target="RFC8349" format="default"/>.</li>
          <li>Stateful NAT44/NAPT management, to optionally specify a port
            set (Port Set Identifier (PSID)) along with its length. A YANG
            module for NAT management is described in <xref
            target="RFC8512"></xref>.</t>

            <t>Stateless target="RFC8512" format="default"/>.</li>
          <li>Stateless NAT46 management, which is required by softwire translation
            based
            softwire-translation-based mechanisms (i.e., the assignment of a
            Network-Specific Prefix to use for IPv4/IPv6 translation). A YANG module for NAT
            management is described in <xref target="RFC8512"></xref>.</t>
          </list></t> target="RFC8512" format="default"/>.</li>
        </ul>
        <t>As YANG modules for the above functions are already defined in
        other documents, their functionality is not duplicated here and they
        should be referred to, as needed. <xref
        target="lw4o6-ce-example"></xref> target="lw4o6-ce-example" format="default"/> provides XML examples of how these
        modules can be used together.</t>
        <t>The CE must already have minimal IPv6 configuration in place so it
        is reachable by the NETCONF client to obtain softwire configuration.
        If additional IPv6 specific IPv6-specific configuration is necessary, the YANG
        modules defined in <xref target="RFC8344"></xref> target="RFC8344" format="default"/> and <xref
        target="RFC8349"></xref> target="RFC8349" format="default"/> may be used.</t>
      </section>
    </section>
    <section anchor="ce-tree-diagram" title="Softwire numbered="true" toc="default">
      <name>Softwire CE YANG Tree Diagram"> Diagram</name>
      <section title="CE numbered="true" toc="default">
        <name>CE Tree Diagram"> Diagram</name>
        <t>The CE module provides configuration and monitoring for all of the
        softwire mechanisms covered in this document (i.e., Lightweight
        4over6, MAP-E, and MAP-T).</t>
        <t>This module augments "ietf-interfaces", defined in <xref
        target="RFC8343"></xref> target="RFC8343" format="default"/> with an entry for the softwire. This entry
        can be referenced to configure IPv4 forwarding features for the
        element. This entry is added only if tunnel type (<xref
        target="iana"></xref>) target="iana" format="default"/>) is set to 'aplusp'.</t>
        <t><xref target="tree-diagram-ce"></xref> target="tree-diagram-ce" format="default"/> shows the tree structure of
        the softwire CE YANG module:</t>
        <figure align="center" anchor="tree-diagram-ce"
                title="Softwire anchor="tree-diagram-ce">
          <name>Softwire CE YANG Tree Diagram">
          <artwork><![CDATA[ Diagram</name>
          <sourcecode name="" type="yangtree"><![CDATA[
module: ietf-softwire-ce
  augment /if:interfaces/if:interface:
    +--rw softwire-payload-mtu?   uint16
    +--rw softwire-path-mru?      uint16
    +--rw (ce-type)?
       +--:(binding) {binding-mode}?
       |  +--rw binding-ipv6info?       union
       |  +--rw br-ipv6-addr            inet:ipv6-address
       +--:(algo) {map-e or map-t}?
          +--rw algo-instances
             +--rw algo-instance* [name]
                +--rw name                string
                +--rw enable?             boolean
                +--rw algo-versioning
                |  +--rw version?   uint64
                |  +--rw date?      yang:date-and-time
                +--rw (data-plane)?
                |  +--:(encapsulation) {map-e}?
                |  |  +--rw br-ipv6-addr        inet:ipv6-address
                |  +--:(translation) {map-t}?
                |     +--rw dmr-ipv6-prefix?    inet:ipv6-prefix
                +--rw ea-len              uint8
                +--rw rule-ipv6-prefix    inet:ipv6-prefix
                +--rw rule-ipv4-prefix    inet:ipv4-prefix
                +--rw forwarding          boolean
  augment /if:interfaces/if:interface/if:statistics:
       +--ro sent-ipv4-packets?
       |       yang:zero-based-counter64
       +--ro sent-ipv4-bytes?
       |       yang:zero-based-counter64
       +--ro sent-ipv6-packets?
       |       yang:zero-based-counter64
       +--ro sent-ipv6-bytes?
       |       yang:zero-based-counter64
       +--ro rcvd-ipv4-packets?
       |       yang:zero-based-counter64
       +--ro rcvd-ipv4-bytes?
       |       yang:zero-based-counter64
       +--ro rcvd-ipv6-packets?
       |       yang:zero-based-counter64
       +--ro rcvd-ipv6-bytes?
       |       yang:zero-based-counter64
       +--ro dropped-ipv4-packets?
       |       yang:zero-based-counter64
       +--ro dropped-ipv4-bytes?
       |       yang:zero-based-counter64
       +--ro dropped-ipv6-packets?
       |       yang:zero-based-counter64
       +--ro dropped-ipv6-bytes?
       |       yang:zero-based-counter64
       +--ro dropped-ipv4-fragments?
       |       yang:zero-based-counter64
       +--ro dropped-ipv4-fragment-bytes?
       |       yang:zero-based-counter64
       +--ro ipv6-fragments-reassembled?
       |       yang:zero-based-counter64
       +--ro ipv6-fragments-bytes-reassembled?
       |       yang:zero-based-counter64
       +--ro out-icmpv4-error-packets?
       |       yang:zero-based-counter64
       +--ro out-icmpv4-error-bytes?
       |       yang:zero-based-counter64
       +--ro out-icmpv6-error-packets?
       |       yang:zero-based-counter64
       +--ro out-icmpv6-error-bytes?
               yang:zero-based-counter64

  notifications:
    +---n softwire-ce-event {binding-mode}?
       +--ro ce-binding-ipv6-addr-change    inet:ipv6-address
     ]]></artwork>
     ]]></sourcecode>
        </figure>
      </section>
      <section anchor="tree-diagram-ce-desc"
               title="Softwire numbered="true" toc="default">
        <name>Softwire CE Tree Diagram Description"> Description</name>
        <t>Additional information related to the operation of a CE element is
        provided below:</t>

        <t><list style="symbols">
            <t>softwire-payload-mtu: optionally

<ul empty="true"><li>
<dl newline="true" indent="3">
          <dt>softwire-payload-mtu:</dt><dd>optionally used to set the IPv4 MTU Maximum Transmission Unit (MTU) for
            the softwire. Needed if the softwire implementation is unable to
            correctly calculate the correct IPv4 Maximum Transit Unit (MTU) MTU
            size automatically.</t>

            <t>softwire-path-mru: optionally automatically.</dd>
          <dt>softwire-path-mru:</dt><dd>optionally used to set the maximum IPv6
            softwire packet size that can be received, including the
            encapsulation/translation overhead. Needed if the softwire
            implementation is unable to correctly calculate the correct IPv4
            payload Maximum Receive Unit (MRU) size automatically (see Section
            3.2 of <xref target="RFC4213"></xref>).</t>

            <t>ce-type: provides target="RFC4213" sectionFormat="of" section="3.2" format="default"/>).</dd>
          <dt>ce-type:</dt><dd>provides a choice statement allowing the binding or
            algorithmic softwire mechanisms to be selected.</t>
          </list></t> selected.</dd>
        </dl>
      </li>
      </ul>
        <t>Further details relevant to binding softwire elements are:</t>

        <t><list style="symbols">
            <t>binding-ipv6info: used are as follows:</t>
<ul empty="true"><li>
        <dl spacing="normal" newline="true">
          <dt>binding-ipv6info:</dt><dd>used to set the IPv6 binding prefix type to
            identify which IPv6 address to use as the tunnel source. It can be
            'ipv6-prefix' or 'ipv6-address'.</t>

            <t>br-ipv6-addr: sets 'ipv6-address'.</dd>
          <dt>br-ipv6-addr:</dt><dd>sets the IPv6 address of the remote BR.</t>
          </list></t> BR.</dd>
        </dl>
      </li>
</ul>
        <t>Additional details relevant to some of the important algorithmic
        elements are provided below:</t>

        <t><list style="symbols">
            <t>algo-versioning: optionally
<ul empty="true"><li>
        <dl spacing="normal" newline="true">
          <dt>algo-versioning:</dt><dd>optionally used to associate a version number
            and/or timestamp to the algorithm. This can be used for
            logging/data retention purposes <xref target="RFC7422"></xref>. target="RFC7422" format="default"/>.
            The version number is selected to uniquely identify the algorithm
            configuration and a new value written whenever a change is made to
            the algorithm or a new algo-instance is created.</t>

            <t>forwarding: specifies created.</dd>
          <dt>forwarding:</dt><dd>specifies whether the rule can be used as a Forward Forwarding
            Mapping Rule (FMR). If not set, this rule is a Basic Mapping Rule
            (BMR) only and must not be used for forwarding. Refer to Section
            4.1 of <xref target="RFC7598"></xref>.</t>

            <t>ea-len: used target="RFC7598" format="default" sectionFormat="of" section="4.1"/>.</dd>
          <dt>ea-len:</dt><dd>used to set the length of the Embedded-Address (EA),
            which is defined in the mapping rule for a MAP domain.</t>

            <t>data-plane: provides domain.</dd>
          <dt>data-plane:</dt><dd>provides a choice statement for either
            encapsulation (MAP-E) or translation (MAP-T).</t>

            <t>br-ipv6-addr: defines (MAP-T).</dd>
          <dt>br-ipv6-addr:</dt><dd>defines the IPv6 address of the BR. This
            information is valid for MAP-E.</t>

            <t>dmr-ipv6-prefix: defines MAP-E.</dd>
          <dt>dmr-ipv6-prefix:</dt><dd>defines the Default Mapping Rule (DMR) IPv6
            prefix of the BR. This information is valid for MAP-T.</t>
          </list></t> MAP-T.</dd>
        </dl>
      </li>
</ul>
        <t>Additional information on the notification node is listed
        below:</t>

        <t><list style="symbols">
            <t>ce-binding-ipv6-addr-change: if
<ul empty="true"><li>
        <dl spacing="normal" newline="true">
          <dt>ce-binding-ipv6-addr-change:</dt><dd>if the CE's binding IPv6 address
            changes for any reason, the NETCONF client will be notified.</t>
          </list></t> notified.</dd>
        </dl>
      </li>
</ul>
      </section>
    </section>
    <section anchor="br-tree-diagram" title="Softwire numbered="true" toc="default">
      <name>Softwire BR YANG Tree Diagram"> Diagram</name>
      <section anchor="br-tree-diagram-com" title="BR numbered="true" toc="default">
        <name>BR Tree Diagram"> Diagram</name>
        <t>The BR YANG module provides configuration and monitoring for all of
        the softwire mechanisms covered in this document (i.e., Lightweight
        4over6, MAP-E, and MAP-T).</t>
        <t><xref target="br-structure"></xref> target="br-structure" format="default"/> provides the tree structure of
        this module:</t>

        <figure align="center" anchor="br-structure"
                title="Softwire anchor="br-structure">
          <name>Softwire BR YANG Tree">
          <artwork><![CDATA[ Tree</name>
          <sourcecode name="" type="yangtree"><![CDATA[
module: ietf-softwire-br
  +--rw br-instances
     +--rw (br-type)?
        +--:(binding) {binding-mode}?
        |  +--rw binding
        |     +--rw bind-instance* [name]
        |        +--rw name                       string
        |        +--rw binding-table-versioning
        |        |  +--rw version?   uint64
        |        |  +--rw date?      yang:date-and-time
        |        +--rw softwire-num-max      uint32
        |        +--rw softwire-payload-mtu       uint16
        |        +--rw softwire-path-mru           uint16
        |        +--rw enable-hairpinning?         boolean
        |        +--rw binding-table
        |        |  +--rw binding-entry* [binding-ipv6info]
        |        |     +--rw binding-ipv6info     union
        |        |     +--rw binding-ipv4-addr?
        |        |     |       inet:ipv4-address
        |        |     +--rw port-set
        |        |     |  +--rw psid-offset?   uint8
        |        |     |  +--rw psid-len       uint8
        |        |     |  +--rw psid           uint16
        |        |     +--rw br-ipv6-addr?
        |        |             inet:ipv6-address
        |        +--rw icmp-policy
        |        |  +--rw icmpv4-errors
        |        |  |  +--rw allow-incoming-icmpv4?    boolean
        |        |  |  +--rw icmpv4-rate?              uint32
        |        |  |  +--rw generate-icmpv4-errors?   boolean
        |        |  +--rw icmpv6-errors
        |        |     +--rw generate-icmpv6-errors?   boolean
        |        |     +--rw icmpv6-rate?              uint32
        |        +--ro traffic-stat
        |           +--ro discontinuity-time   yang:date-and-time
        |           +--ro sent-ipv4-packets?
        |           |       yang:zero-based-counter64
        |           +--ro sent-ipv4-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro sent-ipv6-packets?
        |           |       yang:zero-based-counter64
        |           +--ro sent-ipv6-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro rcvd-ipv4-packets?
        |           |       yang:zero-based-counter64
        |           +--ro rcvd-ipv4-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro rcvd-ipv6-packets?
        |           |       yang:zero-based-counter64
        |           +--ro rcvd-ipv6-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro dropped-ipv4-packets?
        |           |       yang:zero-based-counter64
        |           +--ro dropped-ipv4-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro dropped-ipv6-packets?
        |           |       yang:zero-based-counter64
        |           +--ro dropped-ipv6-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro dropped-ipv4-fragments?
        |           |       yang:zero-based-counter64
        |           +--ro dropped-ipv4-fragment-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro ipv6-fragments-reassembled?
        |           |       yang:zero-based-counter64
        |           +--ro ipv6-fragments-bytes-reassembled?
        |           |       yang:zero-based-counter64
        |           +--ro out-icmpv4-error-packets?
        |           |       yang:zero-based-counter64
        |           +--ro out-icmpv4-error-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro out-icmpv6-error-packets?
        |           |       yang:zero-based-counter64
        |           +--ro out-icmpv6-error-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro dropped-icmpv4-packets?
        |           |       yang:zero-based-counter64
        |           +--ro dropped-icmpv4-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro hairpin-ipv4-packets?
        |           |       yang:zero-based-counter64
        |           +--ro hairpin-ipv4-bytes?
        |           |       yang:zero-based-counter64
        |           +--ro active-softwire-num?
        |                   uint32
        +--:(algo) {map-e or map-t}?
           +--rw algorithm
              +--rw algo-instance* [name]
                 +--rw name                string
                 +--rw enable?             boolean
                 +--rw algo-versioning
                 |  +--rw version?   uint64
                 |  +--rw date?      yang:date-and-time
                 +--rw (data-plane)?
                 |  +--:(encapsulation) {map-e}?
                 |  |  +--rw br-ipv6-addr        inet:ipv6-address
                 |  +--:(translation) {map-t}?
                 |     +--rw dmr-ipv6-prefix?    inet:ipv6-prefix
                 +--rw ea-len              uint8
                 +--rw rule-ipv6-prefix    inet:ipv6-prefix
                 +--rw rule-ipv4-prefix    inet:ipv4-prefix
                 +--rw forwarding          boolean
                 +--rw port-set
                 |  +--rw psid-offset?   uint8
                 |  +--rw psid-len       uint8
                 |  +--rw psid           uint16
                 +--ro traffic-stat
                    +--ro discontinuity-time   yang:date-and-time
                    +--ro sent-ipv4-packets?
                    |       yang:zero-based-counter64
                    +--ro sent-ipv4-bytes?
                    |       yang:zero-based-counter64
                    +--ro sent-ipv6-packets?
                    |       yang:zero-based-counter64
                    +--ro sent-ipv6-bytes?
                    |       yang:zero-based-counter64
                    +--ro rcvd-ipv4-packets?
                    |       yang:zero-based-counter64
                    +--ro rcvd-ipv4-bytes?
                    |       yang:zero-based-counter64
                    +--ro rcvd-ipv6-packets?
                    |       yang:zero-based-counter64
                    +--ro rcvd-ipv6-bytes?
                    |       yang:zero-based-counter64
                    +--ro dropped-ipv4-packets?
                    |       yang:zero-based-counter64
                    +--ro dropped-ipv4-bytes?
                    |       yang:zero-based-counter64
                    +--ro dropped-ipv6-packets?
                    |       yang:zero-based-counter64
                    +--ro dropped-ipv6-bytes?
                    |       yang:zero-based-counter64
                    +--ro dropped-ipv4-fragments?
                    |       yang:zero-based-counter64
                    +--ro dropped-ipv4-fragment-bytes?
                    |       yang:zero-based-counter64
                    +--ro ipv6-fragments-reassembled?
                    |       yang:zero-based-counter64
                    +--ro ipv6-fragments-bytes-reassembled?
                    |       yang:zero-based-counter64
                    +--ro out-icmpv4-error-packets?
                    |       yang:zero-based-counter64
                    +--ro out-icmpv4-error-bytes?
                    |       yang:zero-based-counter64
                    +--ro out-icmpv6-error-packets?
                    |       yang:zero-based-counter64
                    +--ro out-icmpv6-error-bytes?
                            yang:zero-based-counter64

  notifications:
    +---n softwire-binding-instance-event {binding-mode}?
    |  +--ro bind-name?
    |  |       -> /br-instances/binding/bind-instance/name
    |  +--ro invalid-entry*    leafref
    |  +--ro added-entry*      inet:ipv6-address
    |  +--ro modified-entry*   leafref
    +---n softwire-algorithm-instance-event  {map-e, map-t}?
       +--ro algo-name
       |       -> /br-instances/algorithm/algo-instance/name
       +--ro invalid-entry-id*
       |       -> /br-instances/algorithm/algo-instance/name
       +--ro added-entry*
       |       -> /br-instances/algorithm/algo-instance/name
       +--ro modified-entry*
               -> /br-instances/algorithm/algo-instance/name

]]></artwork>

]]></sourcecode>
        </figure>
      </section>
      <section anchor="tree-diagram-br-desc"
               title="Softwire numbered="true" toc="default">
        <name>Softwire BR Tree Diagram Description"> Description</name>
        <t>The descriptions for leaves which that are common with the CE module are
        provided in <xref target="tree-diagram-ce-desc"></xref>. target="tree-diagram-ce-desc" format="default"/>. Descriptions
        for additional elements are provided below:</t>

        <t><list style="symbols">
            <t>binding-table-versioning: optionally
        <ul empty="true" spacing="normal"><li>
	<dl newline="true" indent="3"><dt>binding-table-versioning:</dt><dd>optionally used to associate a
            version number and/or timestamp to the binding table. This can be
            used for logging or data retention purposes <xref
            target="RFC7422"></xref>. target="RFC7422" format="default"/>. The version number is selected to
            uniquely identify the binding table configuration and a new
            timestamp value written whenever a change is made to the contents
            of the binding table or a new binding table list is created.</t>

            <t>binding-entry: used created.</dd>
          <dt>binding-entry:</dt><dd>used to define the binding relationship between
            3-tuples {lwB4's IPv6 address/prefix, the allocated IPv4 address,
            restricted port-set}. port-set}.&nbsp; For detail detailed information, please refer to
            <xref target="RFC7596"></xref>.</t>

            <t>softwire-num-max: used target="RFC7596" format="default"/>.</dd>
          <dt>softwire-num-max:</dt><dd>used to set the maximum number of softwire
            binding rules that can be created on the lw4o6 element
            simultaneously. This paramter parameter must not be set to zero because this
            is equivalent to disabling the BR instance.</t>

            <t>active-softwire-num: holds instance.</dd>
          <dt>active-softwire-num:</dt><dd>holds the number of softwires currently
            provisioned on the BR element.</t>

            <!---
            <t>active (ro): used to show the status of particular
            binding-entry.</t>
IF - Commented out as it isn't in the model any more. I forget what the
intended use for this was. Should it be put back in the model, or can
this descrtiption be removed?
-->
          </list></t> element.</dd>

	</dl></li>
        </ul>
        <t>Additional information on some of the important notification nodes
        is listed below:</t>

        <t><list style="symbols">
            <t>invalid-entry,
        <ul empty="true" spacing="normal"><li>
<dl newline="true" indent="3"><dt>invalid-entry, added-entry, modified-entry: used modified-entry:</dt><dd>used to notify the
            NETCONF client that a specific binding entry or MAP rule has
            expired, been invalidated, added, or modified.</t>
          </list></t> modified.</dd>
</dl></li>
        </ul>
      </section>
    </section>
    <section anchor="ce-yang-module" title="Softwire numbered="true" toc="default">
      <name>Softwire CE YANG Module"> Module</name>
      <t>This module imports the modules defined in <xref
      target="RFC6991"></xref>, target="RFC6991"
      format="default"/>, <xref target="RFC8343"></xref>, target="RFC8343" format="default"/>, and <xref
      target="RFC7224"></xref>.
      target="RFC7224" format="default"/>. It also imports the
      'ietf-softwire-common' and 'iana-tunnel-type' modules <xref
      target="I-D.ietf-softwire-iftunnel"></xref>.</t>

      <figure>
        <artwork><![CDATA[<CODE BEGINS>file "ietf-softwire-ce@2019-01-11.yang" target="RFC8675"
      format="default"/>.</t>

      <sourcecode name="ietf-softwire-ce@2019-10-28.yang" type="yang" markers="true"><![CDATA[
module ietf-softwire-ce {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-softwire-ce";
  prefix softwire-ce;

  import ietf-inet-types {
    prefix inet;
    reference "Section 4 of RFC 6991";
      "RFC 6991: Common YANG Data Types, Section 4";
  }
  import ietf-interfaces {
    prefix if;
    reference
      "RFC 8343: A YANG Data Model for Interface Management";
  }
  import ietf-softwire-common {
    prefix softwire-common;
    reference
      "RFC XXXX: 8676: YANG Modules for IPv4-in-IPv6 Address plus Port
       Softwires";
  }
  import iana-tunnel-type {
    prefix iana-tunnel-type;
    reference
      "RFC YYYY: 8675: A YANG Data Model for Tunnel Interface Types YANG Module"; Types";
  }

  organization
    "IETF Softwire Working Group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/softwire/>
     WG List:  <mailto:softwire@ietf.org>

     Author:  Qi Sun
              <mailto:sunqi.ietf@gmail.com>

     Author:  Linhui Sun
              <mailto:lh.sunlinh@gmail.com>

     Author:  Yong Cui
              <mailto:yong@csnet1.cs.tsinghua.edu.cn>

     Editor:  Ian Farrer
              <mailto:ian.farrer@telekom.de>

     Author:  Sladjana Zoric
              <mailto:sladjana.zoric@telekom.de>

     Editor:  Mohamed Boucadair
              <mailto:mohamed.boucadair@orange.com>

     Author:  Rajiv Asati
               <mailto:rajiva@cisco.com>";
  description
    "This document defines a YANG module for the configuration and
     management of A+P Softwire Customer Premises Equipment (CEs).
     It covers Lightweight 4over6, MAP-E, and MAP-T mechanisms.

     Copyright (c) 2019 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

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

     This version of this YANG module is part of RFC XXXX; 8676; see
     the RFC itself for full legal notices.";

  revision 2019-01-11 2019-10-28 {
    description
      "Initial revision.";
    reference
      "RFC XXXX: 8676: YANG Modules for IPv4-in-IPv6 Address plus Port
       (A+P) Softwires";
  }

  /*
   * Features
   */

  feature binding-mode {
    description
      "Binding is used for configuring the Lightweight 4over6 mechanism.

       Binding based

       Binding-based softwire mechanisms are IPv4-over-IPv6 tunnelling tunneling
       transition mechanisms specifically intended for complete
       independence between the IPv6 subnet prefix (and IPv6 address)
       and IPv4 address, with or without IPv4 address sharing.

       This is accomplished by maintaining state for each softwire
       (per-subscriber state) in the central Border Relay (BR) and using
       a hub-and-spoke forwarding architecture.  In order to delegate
       the NAPT function and achieve IPv4 address sharing,
       port-restricted IPv4 addresses needs to be allocated to CEs.

       This feature indicates that the network element can function as
       one or more binding based binding-based softwire instances.";
    reference
      "RFC7596:
      "RFC 7596: Lightweight 4over6: An Extension to the Dual-Stack Lite
       Architecture
       RFC7597:
       RFC 7597: Mapping of Address and Port with Encapsulation (MAP-E)
       RFC7599:
       RFC 7599: Mapping of Address and Port using Translation (MAP-T)";
  }

  feature map-e {
    description
      "MAP-E is an IPv6 transition mechanism for transporting IPv4
       packets across an IPv6 network using IP encapsulation.  MAP-E
       allows for a reduction of the amount of centralized state using
       rules to express IPv4/IPv6 address mappings.  This introduces an
       algorithmic relationship between the IPv6 subnet and IPv4
       address.

       This feature indicates that the network element can function as
       one or more MAP-E softwire instances.";
    reference
      "RFC7597:
      "RFC 7597: Mapping of Address and Port with
       Encapsulation (MAP-E)";
  }

  feature map-t {
    description
      "MAP-T is an IPv6 transition mechanism for transporting IPv4
       packets across an IPv6 network using IP translation.  It
       leverages a double stateless NAT64 based NAT64-based solution as well as
       the stateless algorithmic address & and transport layer port
       mapping algorithm defined for MAP-E.

       This feature indicates that the network element can function as
       one or more MAP-T softwire instances.";
    reference
      "RFC7599:
      "RFC 7599: Mapping of Address and Port using Translation (MAP-T)";
  }

  // Binding Entry

  grouping binding-entry {
    description
      "The binding BR (Border Relay) maintains an address binding table
       that contains the binding between the CE's IPv6 address,
       the allocated IPv4 address address, and the restricted port-set.";
    leaf binding-ipv6info {
      type union {
        type inet:ipv6-address;
        type inet:ipv6-prefix;
      }
      description
        "The IPv6 information for a binding entry.

         When the IPv6 prefix type is used,
         the IPv6 source address of the CE is constructed
         according to the description in RFC7596. RFC 7596.

         If the IPv6 address type is used, the CE can use
         any valid /128 address from a prefix assigned to
         the CE.";
      reference "Section 5.1 of RFC7596.";
        "RFC 7596: Lightweight 4over6: An Extension
         to the Dual-Stack Lite Architecture, Section 5.1";
    }
    leaf br-ipv6-addr {
      type inet:ipv6-address;
      mandatory true;
      description
        "The IPv6 address of the binding BR.";
    }
  }

  // configuration and stateful parameters for softwire CE interface

  augment "/if:interfaces/if:interface" {
    when "derived-from(if:type, 'iana-tunnel-type:aplusp')";
    description
      "Softwire CE interface configuration";
    leaf softwire-payload-mtu {
      type uint16;
      units "bytes";
      description
        "The payload IPv4 MTU for the softwire tunnel.";
    }
    leaf softwire-path-mru {
      type uint16;
      units "bytes";
      description
        "The path MRU for the softwire (payload + encapsulation
         overhead).";
      reference
        "RFC 4213: Basic Transition Mechanisms for IPv6 Hosts and
         Routers";
    }
    choice ce-type {
      description
        "Sets the softwire CE mechanism";
      case binding {
        if-feature "binding-mode";
        description
          "CE binding configuration";
        uses binding-entry;
      }
      case algo {
        if-feature "map-e or map-t";
        description
          "CE algorithm configuration";
        container algo-instances {
          description
            "Collection of MAP-E/MAP-T parameters";
          list algo-instance {
            key "name";
            description
              "MAP forwarding rule instance for
               MAP-E/MAP-T";
            leaf name {
              type string;
              mandatory true;
              description
                "The name is used to uniquely identify an algorithm
                 instance.

                 This name can be automatically assigned
                 or explicitly configured.";
            }
            uses softwire-common:algorithm-instance;
          }
        }
      }
    }
  }
  augment "/if:interfaces/if:interface/if:statistics" {
    when "derived-from(../if:type, 'iana-tunnel-type:aplusp')";
    description
      "Softwire CE interface statistics.";
    uses softwire-common:traffic-stat;
  }

  /*
   * Notifications
   */

  notification softwire-ce-event {
    if-feature "binding-mode";
    description
      "CE notification";
    leaf ce-binding-ipv6-addr-change {
      type inet:ipv6-address;
      mandatory true;
      description
        "This notification is generated whenever the CE's binding IPv6
         address changes for any reason.";
    }
  }
}
<CODE ENDS>
        ]]></artwork>
      </figure>
]]></sourcecode>
    </section>
    <section anchor="br-yang-module" title="BR numbered="true" toc="default">
      <name>BR Softwire YANG Module"> Module</name>
      <t>This module imports typedefs from <xref target="RFC6991"></xref>. target="RFC6991" format="default"/>. It
      also imports the 'ietf-softwire-common' module.</t>

      <figure>
        <artwork><![CDATA[<CODE BEGINS>file "ietf-softwire-br@2019-01-11.yang"
      <sourcecode name="ietf-softwire-br@2019-10-28.yang" type="yang" markers="true"><![CDATA[
module ietf-softwire-br {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-softwire-br";
  prefix softwire-br;

  import ietf-inet-types {
    prefix inet;
    reference "Section 4 of RFC 6991";
      "RFC 6991: Common YANG Data Types, Section 4";
  }
  import ietf-yang-types {
    prefix yang;
    reference "Section 3 of RFC 6991";
      "RFC 6991: Common YANG Data Types, Section 3";
  }
  import ietf-softwire-common {
    prefix softwire-common;
    reference
      "RFC XXXX: 8676: YANG Modules for IPv4-in-IPv6 Address plus Port
       (A+P) Softwires";
  }

  organization
    "IETF Softwire Working Group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/softwire/>
     WG List:  <mailto:softwire@ietf.org>

     Author:  Qi Sun
              <mailto:sunqi.ietf@gmail.com>

     Author:  Linhui Sun
              <mailto:lh.sunlinh@gmail.com>

     Author:  Yong Cui
              <mailto:yong@csnet1.cs.tsinghua.edu.cn>

     Editor:  Ian Farrer
              <mailto:ian.farrer@telekom.de>

     Author:  Sladjana Zoric
              <mailto:sladjana.zoric@telekom.de>

     Editor:  Mohamed Boucadair
              <mailto:mohamed.boucadair@orange.com>

     Author:  Rajiv Asati
               <mailto:rajiva@cisco.com>";

  description
    "This document defines a YANG module for the configuration and
     management of A+P Softwire Border Routers.  It covers Lightweight
     4over6, MAP-E, and MAP-T mechanisms.

     Copyright (c) 2019 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

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

     This version of this YANG module is part of RFC XXXX; 8676; see
     the RFC itself for full legal notices.";

  revision 2019-01-11 2019-10-28 {
    description
      "Initial revision.";
    reference
      "RFC XXXX: 8676: YANG Modules for IPv4-in-IPv6 Address plus Port
       (A+P) Softwires";
  }

  /*
   * Groupings
   */

  grouping port-set {
    description
      "Describes a set of layer Layer 4 port numbers.

       This may be a simple port range, or use the Port Set
       Identifier (PSID) algorithm to represent a range of transport
       layer ports which that will be used by a NAPT.";
    leaf psid-offset {
      type uint8 {
        range "0..16";
      }
      description
        "The number of offset bits.  In Lightweight 4over6,
         the default value is 0 for assigning one contiguous
         port range.  In MAP-E/T, the default value is 6,
         which means the system ports (0-1023) are excluded by
         default and the assigned port ranges are distributed across
         the entire port space, depending on either psid-len or the
         number of contiguous ports.";
    }
    leaf psid-len {
      type uint8 {
        range "0..15";
      }
      mandatory true;
      description
        "The length of PSID, representing the sharing
         ratio for an IPv4 address.  This, along with ea-len, can
         be used to calculate the number of contiguous ports per
         port range";
    }
    leaf psid {
      type uint16;
      mandatory true;
      description
        "Port Set Identifier (PSID) value, which
         identifies a set of ports algorithmically.";
    }
  }

  grouping binding-entry {
    description
      "The binding BR maintains an address binding table that
       contains the binding between the CE's IPv6 address,
       the allocated IPv4 address and restricted port-set.";
    leaf binding-ipv6info {
      type union {
        type inet:ipv6-address;
        type inet:ipv6-prefix;
      }
      description
        "The IPv6 information for a CE binding entry.
         When the IPv6 prefix type is used,
         the IPv6 source address of the CE is constructed
         according to the description in RFC7596; RFC 7596;
         if the IPv6 address type is used, the CE can use
         any valid /128 address from a prefix assigned to
         the CE.";
      reference
        "RFC7596:
        "RFC 7596: Lightweight 4over6: An Extension to the Dual-Stack
         Lite Architecture";
    }
    leaf binding-ipv4-addr {
      type inet:ipv4-address;
      description
        "The IPv4 address assigned to the binding CE,
         which is used as the IPv4 external address
         for binding CE local NAPT44.";
    }
    container port-set {
      description
        "For Lightweight 4over6, the default value
         for offset should be 0, to configure one contiguous
         port range.";
      uses port-set {
        refine "psid-offset" {
          default "0";
        }
      }
    }
    leaf br-ipv6-addr {
      type inet:ipv6-address;
      description
        "The IPv6 address for binding BR.";
    }
  }

  /*
   * Features
   */

  feature binding-mode {
    description
      "Binding is used for configuring the Lightweight 4over6 mechanism.

       Binding based

       Binding-based softwire mechanisms are IPv4-over-IPv6 tunnelling tunneling
       transition mechanisms specifically intended for complete
       independence between the IPv6 subnet prefix (and IPv6 address)
       and IPv4 address, with or without IPv4 address sharing.

       This is accomplished by maintaining state for each softwire
       (per-subscriber state) in the central Border Relay (BR) and using
       a hub-and-spoke forwarding architecture.  In order to delegate
       the NAPT function and achieve IPv4 address sharing,
       port-restricted IPv4 addresses needs to be allocated to CEs.

       This feature indicates that the network element can function as
       one or more binding based binding-based softwire instances.";
    reference
      "RFC7596:
      "RFC 7596: Lightweight 4over6: An Extension to the Dual-Stack Lite
       Architecture
       RFC7597:
       RFC 7597: Mapping of Address and Port with Encapsulation (MAP-E)
       RFC7599:
       RFC 7599: Mapping of Address and Port using Translation (MAP-T)";
  }

  feature map-e {
    description
      "MAP-E is an IPv6 transition mechanism for transporting IPv4
       packets across an IPv6 network using IP encapsulation.  MAP-E
       allows for a reduction of the amount of centralized state using
       rules to express IPv4/IPv6 address mappings.  This introduces an
       algorithmic relationship between the IPv6 subnet and IPv4
       address.

       This feature indicates that the network element can function as
       one or more MAP-E softwire instances.";
    reference
      "RFC7597:
      "RFC 7597: Mapping of Address and Port with Encapsulation
       (MAP-E)";
  }

  feature map-t {
    description
      "MAP-T is an IPv6 transition mechanism for transporting IPv4
       packets across an IPv6 network using IP translation.  It
       leverages a double stateless NAT64 based NAT64-based solution as well
       as the stateless algorithmic address & and transport layer
       port mapping algorithm defined for MAP-E.

       This feature indicates that the network element can function as
       one or more MAP-T softwire instances.";
    reference
      "RFC7599:
      "RFC 7599: Mapping of Address and Port using Translation (MAP-T)";
  }

  container br-instances {
    description
      "BR instances enabled in a network element.";
    choice br-type {
      description
        "Select binding or algorithmic BR functionality.";
      case binding {
        if-feature "binding-mode";
        container binding {
          description
            "binding mechanism (binding table) configuration.";
          list bind-instance {
            key "name";
            description
              "A set of binding instances to be configured.";
            leaf name {
              type string;
              mandatory true;
              description
                "The name for the binding BR.  It is used to uniquely
                 distinguish a binding instance by its name.";
            }
            container binding-table-versioning {
              description
                "binding table's version";
              leaf version {
                type uint64;
                description
                  "Version number for this binding table.";
              }
              leaf date {
                type yang:date-and-time;
                description
                  "Timestamp when the binding table was activated.

                   A binding instance may be provided with binding
                   entries that may change in time (e.g., increase
                   the size of the port set).  When a party who is the
                   victim of abuse presents an external IP address/port,
                   the version of the binding table is important
                   because
                   because, depending on the version, a distinct
                   customer may be identified.

                   The timestamp is used as a key to find the
                   appropriate binding table that was put into effect
                   when an abuse occurred.";
                reference
                  "RFC7422:
                  "RFC 7422: Deterministic Address Mapping to Reduce
                   Logging in Carrier-Grade NAT Deployments";
              }
            }
            leaf softwire-num-max {
              type uint32 {
                range "1..max";
              }
              mandatory true;
              description
                "The maximum number of softwires that can be created
                 on the binding BR.";
            }
            leaf softwire-payload-mtu {
              type uint16;
              units "bytes";
              mandatory true;
              description
                "The payload IPv4 MTU for binding softwire.";
            }
            leaf softwire-path-mru {
              type uint16;
              units "bytes";
              mandatory true;
              description
                "The path MRU for binding softwire."; softwire";
              reference
                "RFC4213:
                "RFC 4213: Basic Transition Mechanisms for IPv6 Hosts
                           and Routers";
            }
            leaf enable-hairpinning {
              type boolean;
              default "true";
              description
                "Enables/disables support for locally forwarding
                 (hairpinning) traffic between two CEs."; CEs";
              reference "Section 6.2 of RFC7596";
                "RFC 7596: Lightweight 4over6: An Extension to
                 the Dual-Stack Lite Architecture, Section 6.2";
            }
            container binding-table {
              description
                "binding table";
              list binding-entry {
                key "binding-ipv6info";
                description
                  "binding entry";
                uses binding-entry;
              }
            }
            container icmp-policy {
              description
                "The binding BR can be configured to process or drop
                 incoming ICMP messages, messages and to generate outgoing ICMP
                 error messages.";
              container icmpv4-errors {
                description
                  "ICMPv4 error processing configuration";
                leaf allow-incoming-icmpv4 {
                  type boolean;
                  default "true";
                  description
                    "Enables the processing of incoming ICMPv4
                     packets.";
                  reference
                    "RFC7596:
                    "RFC 7596: Lightweight 4over6: An Extension to
                     the Dual-Stack Lite Architecture";
                }
                leaf icmpv4-rate {
                  type uint32;
                  description
                    "Rate limit threshold in messages per-second per second
                     for processing incoming ICMPv4 errors messages";
                }
                leaf generate-icmpv4-errors {
                  type boolean;
                  default "true";
                  description
                    "Enables the generation of outgoing ICMPv4 error
                     messages on receipt of an inbound IPv4 packet
                     with no matching binding table entry.";
                  reference "Seciton 5.2 of RFC7596.";
                    "RFC 7596: Lightweight 4over6:
                     An Extension to the Dual-Stack Lite
                     Architecture, Section 5.2";
                }
              }
              container icmpv6-errors {
                description
                  "ICMPv6 error processing configuration";
                leaf generate-icmpv6-errors {
                  type boolean;
                  default "true";
                  description
                    "Enables the generation of ICMPv6 error messages if
                     no matching binding table entry is found for a
                     received packet.";
                  reference "Section 6.2 of RFC7596.";
                    "RFC 7596: Lightweight 4over6:
                     An Extension to the Dual-Stack Lite
                     Architecture, Section 6.2";
                }
                leaf icmpv6-rate {
                  type uint32;
                  description
                    "Rate limit threshold in messages per-second per second
                     for sending ICMPv6 errors messages";
                  reference "Section 9 of RFC7596.";
                    "RFC 7596: Lightweight 4over6: An Extension
                     to the Dual-Stack Lite Architecture, Section 9";
                }
              }
            }
            container traffic-stat {
              config false;
              description
                "Traffic statistics information for the BR.";
              leaf discontinuity-time {
                type yang:date-and-time;
                mandatory true;
                description
                  "The time of the most recent occasion on which the BR
                   instance suffered a discontinuity.  This must be
                   initialized when the BR instance is configured
                   or rebooted.";
              }
              uses softwire-common:traffic-stat;
              leaf dropped-icmpv4-packets {
                type yang:zero-based-counter64;
                description
                  "ICMPv4 packets that are dropped as a result
                   of the ICMP policy.  Typically, this can be any
                   incoming ICMPv4 packets if ICMPv4 processing is
                   disabled or incoming ICMPv4 packets that exceed
                   the ICMPv4 rate-limit threshold.

                   Discontinuities in the value of this counter can
                   occur at re-initialization of the management
                   system,
                   system and at other times as indicated by
                   the value of 'discontinuity-time'.";
              }
              leaf dropped-icmpv4-bytes {
                type yang:zero-based-counter64;
                description
                  "ICMPv4 messages, in bytes, that are dropped as
                   a result of the ICMP policy.  Typically, it
                   can be any incoming ICMPv4 packets if ICMPv4
                   processing is disabled or incoming ICMPv4
                   packets that exceed the ICMPv4 rate-limit
                   threshold.

                   Discontinuities in the value of this counter can
                   occur at re-initialization of the management
                   system,
                   system and at other times as indicated by
                   the value of 'discontinuity-time'.";
              }
              leaf hairpin-ipv4-packets {
                type yang:zero-based-counter64;
                description
                  "IPv4 packets locally routed between two CEs
                   (hairpinned).

                   Discontinuities in the value of this counter can
                   occur at re-initialization of the management
                   system,
                   system and at other times as indicated by
                   the value of 'discontinuity-time'.";
              }
              leaf hairpin-ipv4-bytes {
                type yang:zero-based-counter64;
                description
                  "IPv4 bytes locally routed between two CEs
                   (hairpinned).

                   Discontinuities in the value of this counter can
                   occur at re-initialization of the management
                   system,
                   system and at other times as indicated by
                   the value of 'discontinuity-time'.";
              }
              leaf active-softwire-num {
                type uint32;
                config false;
                description
                  "The number of currently active softwires on the
                   binding instance.

                   Discontinuities in the value of this counter can
                   occur at re-initialization of the management
                   system,
                   system and at other times as indicated by
                   the value of 'discontinuity-time'.";
              }
            }
          }
        }
      }
      case algo {
        if-feature "map-e or map-t";
        container algorithm {
          description
            " A
            "A set of parameters used for MAP-E/MAP-T."; MAP-E/MAP-T";
          list algo-instance {
            key "name";
            description
              "Instances of algorithm";
            leaf name {
              type string;
              mandatory true;
              description
                "The name is used to uniquely identify an algorithm
                 instance.

                 This name can be automatically assigned
                 or explicitly configured.";
            }
            uses softwire-common:algorithm-instance;
            container port-set {
              description
                "Indicates a set of ports.";
              uses port-set;
            }
            container traffic-stat {
              config false;
              description
                "Traffic statistics information for the BR.";
              leaf discontinuity-time {
                type yang:date-and-time;
                mandatory true;
                description
                  "The time of the most recent occasion on which the BR
                   instance suffered a discontinuity.  This must be
                   reset to the current date-and-time when the BR
                   instance is configured or rebooted.";
              }
              uses softwire-common:traffic-stat;
            }
          }
        }
      }
    }
  }

  /*
   * Notifications
   */

  notification softwire-binding-instance-event {
    if-feature "binding-mode";
    description
      "Notifications for the binding instance when an entry is
       added, modified, or is not valid anymore.";
    leaf bind-name {
      type leafref {
        path "/br-instances/binding/bind-instance/name";
      }
      description
        "The name of the binding-instance that
         generated the notification.";
    }
    leaf-list invalid-entry {
      type leafref {
        path "/br-instances/binding/"
           + "bind-instance[name=current()/../bind-name]/"
           + "binding-table/binding-entry/binding-ipv6info";
      }
      description
        "Notify the client that a specific binding entry has
         expired or is invalid.  The binding-ipv6info identifies
         an entry.";
    }
    leaf-list added-entry {
      type inet:ipv6-address;
      description
        "Notify the client that a binding entry has been added.
         The ipv6 IPv6 address of that entry is the index.  The client
         gets other information from the binding BR about the entry
         indexed by that ipv6 address.";
    }
    leaf-list modified-entry {
      type leafref {
        path "/br-instances/binding/"
           + "bind-instance[name=current()/../bind-name]/"
           + "binding-table/binding-entry/binding-ipv6info";
      }
      description
        "The binding-table binding table entry that has been modified.";
    }
  }
  notification softwire-algorithm-instance-event {
    if-feature "map-e or map-t";
    description
      "Notifications for an algorithm instance when an entry is
       added, modified, or is not valid anymore.";
    leaf algo-name {
      type leafref {
        path "/br-instances/algorithm/algo-instance/name";
      }
      mandatory true;
      description
        "algorithmic
        "Algorithmic instance event.";
    }
    leaf-list invalid-entry {
      type leafref {
        path "/br-instances/algorithm/algo-instance/name";
      }
      description
        "Invalid entry event."; entry.";
    }
    leaf-list added-entry {
      type leafref {
        path "/br-instances/algorithm/algo-instance/name";
      }
      description
        "Added entry.";
    }
    leaf-list modified-entry {
      type leafref {
        path "/br-instances/algorithm/algo-instance/name";
      }
      description
        "Modified entry.";
    }
  }
}
<CODE ENDS>
        ]]></artwork>
      </figure>
]]></sourcecode>
    </section>
    <section anchor="commons-softwire-elements"
             title="Common numbered="true" toc="default">
      <name>Common Softwire Element Groups YANG Module"> Module</name>
      <t>This module imports typedefs from <xref target="RFC6991"></xref>.</t> target="RFC6991" format="default"/>.</t>
      <t>The following YANG module contains definitions that are used by both
      the softwire CE and softwire BR YANG modules.</t>

      <figure>
        <artwork><![CDATA[<CODE BEGINS>file "ietf-softwire-common@2019-01-11.yang"

      <sourcecode name="ietf-softwire-common@2019-10-28.yang" type="yang" markers="true"><![CDATA[
module ietf-softwire-common {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-softwire-common";
  prefix softwire-common;

  import ietf-inet-types {
    prefix inet;
    reference "Section 4 of RFC 6991";
      "RFC 6991: Common YANG Data Types, Section 4";
  }
  import ietf-yang-types {
    prefix yang;
    reference "Section 3 of RFC 6991";
      "RFC 6991: Common YANG Data Types, Section 3";
  }

  organization
    "IETF Softwire Working Group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/softwire/>
     WG List:  <mailto:softwire@ietf.org>

     Author:  Qi Sun
              <mailto:sunqi.ietf@gmail.com>

     Author:  Linhui Sun
              <mailto:lh.sunlinh@gmail.com>

     Author:  Yong Cui
              <mailto:yong@csnet1.cs.tsinghua.edu.cn>

     Editor:  Ian Farrer
              <mailto:ian.farrer@telekom.de>

     Author:  Sladjana Zoric
              <mailto:sladjana.zoric@telekom.de>

     Editor:  Mohamed Boucadair
              <mailto:mohamed.boucadair@orange.com>

     Author:  Rajiv Asati
               <mailto:rajiva@cisco.com>";
  description
    "This document defines a YANG module defining types
     common to all A+P modules.

     Copyright (c) 2019 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

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

     This version of this YANG module is part of RFC XXXX; 8676; see
     the RFC itself for full legal notices.";

  revision 2019-01-11 2019-10-28 {
    description
      "Initial revision.";
    reference
      "RFC XXXX: 8676: YANG Modules for IPv4-in-IPv6 Address plus Port
                 (A+P) Softwires";
  }

  feature map-e {
    description
      "MAP-E is an IPv6 transition mechanism for transporting IPv4
       packets across an IPv6 network using IP encapsulation.  MAP-E
       allows for a reduction of the amount of centralized state using
       rules to express IPv4/IPv6 address mappings.  This introduces an
       algorithmic relationship between the IPv6 subnet and IPv4
       address.

       This feature indicates that the network element can function as
       one or more MAP-E softwire instances.";
    reference
      "RFC7597:
      "RFC 7597: Mapping of Address and Port with Encapsulation
       (MAP-E)";
  }

  feature map-t {
    description
      "MAP-T is an IPv6 transition mechanism for transporting IPv4
       packets across an IPv6 network using IP translation.  It
       leverages a double stateless NAT64 based NAT64-based solution as well as
       the stateless algorithmic address & and transport layer
       port mapping algorithm defined for MAP-E.

       This feature indicates that the network element can function as
       one or more MAP-T softwire instances.";
    reference
      "RFC7599:
      "RFC 7599: Mapping of Address and Port using Translation (MAP-T)";
  }

  /*
   * Groupings
   */

  grouping algorithm-instance {
    description
      "A collection of parameters that is used fro for MAP-E/MAP-T.";
    leaf enable {
      type boolean;
      description
        "Enable/disable an individual MAP-E or MAP-T rule.";
    }
    container algo-versioning {
      description
        "Version number for this algorithm instance";
      leaf version {
        type uint64;
        description
          "A version number for the mapping algorithm
           rules provided to the algorithm instance";
      }
      leaf date {
        type yang:date-and-time;
        description
          "Timestamp when the algorithm instance was activated.

           An algorithm instance may be provided with mapping
           rules that may change in time (for example, increase
           the size of the port set).  When a party who is the victim
           of abuse presents an external IP address/port, the version
           of the algorithm is important because depending on
           the version, a distinct customer may be identified.

           The timestamp is used as a key to find the appropriate
           algorithm that was put into effect when an abuse
           occurred. ";
           occurred.";
        reference
          "RFC7422:
          "RFC 7422: Deterministic Address Mapping to Reduce
                     Logging in Carrier-Grade NAT Deployments";
      }
    }
    choice data-plane {
      description
        "Selects MAP-E (encapsulation) or MAP-T
         (translation)";
      case encapsulation {
        if-feature "map-e";
        description
          "encapsulation for MAP-E";
        leaf br-ipv6-addr {
          type inet:ipv6-address;
          mandatory true;
          description
            "The IPv6 address of the MAP-E BR.";
        }
      }
      case translation {
        if-feature "map-t";
        description
          "translation for MAP-T";
        leaf dmr-ipv6-prefix {
          type inet:ipv6-prefix;
          description
            "The IPv6 prefix of the MAP-T BR.";
        }
      }
    }
    leaf ea-len {
      type uint8;
      mandatory true;
      description
        "Embedded Address (EA) bits are the IPv4 EA-bits in the IPv6
         address identifying an IPv4 prefix/address (or part thereof)
         or a shared IPv4 address (or part thereof) and a port-set
         identifier.  The length of the EA-bits is defined as part of
         a MAP rule for a MAP domain.";
    }
    leaf rule-ipv6-prefix {
      type inet:ipv6-prefix;
      mandatory true;
      description
        "The Rule IPv6 prefix defined in the mapping rule.";
    }
    leaf rule-ipv4-prefix {
      type inet:ipv4-prefix;
      mandatory true;
      description
        "The Rule IPv4 prefix defined in the mapping rule.";
    }
    leaf forwarding {
      type boolean;
      mandatory true;
      description
        "This parameter specifies whether the rule may be used for
         forwarding (FMR). If
         forwarding; if set, this rule is used as an FMR; a Forwarding
         Mapping Rule (FMR); if not set, this rule is a Basic
         Mapping Rule (BMR) only and must not be used for forwarding.";
    }
  }

  grouping traffic-stat {
    description
      "Traffic statistics";
    leaf sent-ipv4-packets {
      type yang:zero-based-counter64;
      description
        "Number of decapsulated and forwarded IPv4 packets.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf sent-ipv4-bytes {
      type yang:zero-based-counter64;
      description
        "Decapsulated/translated IPv4 traffic sent, in bytes bytes.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf sent-ipv6-packets {
      type yang:zero-based-counter64;
      description
        "Number of encapsulated IPv6 packets sent.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf sent-ipv6-bytes {
      type yang:zero-based-counter64;
      description
        "Encapsulated IPv6 traffic sent, in bytes bytes.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf rcvd-ipv4-packets {
      type yang:zero-based-counter64;
      description
        "Number of IPv4 packets received.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf rcvd-ipv4-bytes {
      type yang:zero-based-counter64;
      description
        "IPv4 traffic received, in bytes.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf rcvd-ipv6-packets {
      type yang:zero-based-counter64;
      description
        "Number of IPv4-in-IPv6 packets received.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf rcvd-ipv6-bytes {
      type yang:zero-based-counter64;
      description
        "IPv4-in-IPv6 traffic received, in bytes.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf dropped-ipv4-packets {
      type yang:zero-based-counter64;
      description
        "Number of IPv4 packets dropped at the
         Internet-facing interface.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf dropped-ipv4-bytes {
      type yang:zero-based-counter64;
      description
        "IPv4 traffic dropped at the Internet-facing
         interface, in bytes.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf dropped-ipv6-packets {
      type yang:zero-based-counter64;
      description
        "Number of IPv4-in-IPv6 packets dropped.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf dropped-ipv6-bytes {
      type yang:zero-based-counter64;
      description
        "IPv4-in-IPv6 traffic dropped, in bytes.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf dropped-ipv4-fragments {
      type yang:zero-based-counter64;
      description
        "Number of fragmented IPv4 packets dropped.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf dropped-ipv4-fragment-bytes {
      type yang:zero-based-counter64;
      description
        "Fragmented IPv4 traffic dropped, in bytes.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf ipv6-fragments-reassembled {
      type yang:zero-based-counter64;
      description
        "Number of IPv6 fragments successfully reassembled.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf ipv6-fragments-bytes-reassembled {
      type yang:zero-based-counter64;
      description
        "IPv6 fragments successfully reassembled, in bytes.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf out-icmpv4-error-packets {
      type yang:zero-based-counter64;
      description
        "Internally generated ICMPv4 error packets.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf out-icmpv4-error-bytes {
      type yang:zero-based-counter64;
      description
        "Internally generated ICMPv4 error messages, in bytes.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf out-icmpv6-error-packets {
      type yang:zero-based-counter64;
      description
        "Internally generated ICMPv6 error packets.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
    leaf out-icmpv6-error-bytes {
      type yang:zero-based-counter64;
      description
        "Internally generated ICMPv6 error messages, in bytes.

         Discontinuities in the value of this counter can occur
         at re-initialization of the management system, system and at
         other times as indicated by the value of
         'discontinuity-time'.";
    }
  }
}
<CODE ENDS>                 ]]></artwork>
      </figure>
]]></sourcecode>
    </section>
    <section anchor="security" title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>

      <t>The YANG modules defined in this document is are designed to be accessed
      via network management protocols such as NETCONF <xref
      target="RFC6241"></xref> target="RFC6241" format="default"/> or RESTCONF <xref target="RFC8040"></xref>. target="RFC8040" format="default"/>. The
      lowest NETCONF layer is the secure transport layer, and the
      mandatory-to-implement secure transport is Secure Shell (SSH) <xref
      target="RFC6242"></xref>. target="RFC6242" format="default"/>. The lowest RESTCONF layer is HTTPS, and the
      mandatory-to-implement secure transport is TLS <xref
      target="RFC8446"></xref>.</t> target="RFC8446" format="default"/>.</t>
      <t>The NETCONF access control model Network Configuration Access Control Model (NACM) <xref target="RFC8341"></xref> target="RFC8341" format="default"/>
      provides the means to restrict access for particular NETCONF or RESTCONF
      users to a preconfigured subset of all available NETCONF or RESTCONF
      protocol operations and content.</t>

      <t>All data nodes defined in the YANG modules which can be created,
      modified, and deleted (i.e., config true, which is the default) are
      considered sensitive. Write operations (e.g., edit-config) applied to
      these data nodes without proper protection can negatively affect have a negative
      effect on network
      operations. An attacker who is able to access the BR can undertake
      various attacks, such as:</t>

      <t><list style="symbols">
          <t>Setting
      <ul spacing="normal">
        <li>Setting the value of 'br-ipv6-addr' on the CE to point to an
          illegitimate BR so that it can intercept all the traffic sent by a
          CE. Illegitimately intercepting users' traffic is an attack with
          severe implications on privacy.</t>

          <t>Setting privacy.</li>
        <li>Setting the MTU to a low value, which may increase the number of
          fragments ('softwire-payload-mtu').</t>

          <t>Disabling ('softwire-payload-mtu').</li>
        <li>Disabling hairpinning (i.e., setting 'enable-hairpinning' to
          'false') to prevent communications between CEs.</t>

          <t>Setting CEs.</li>
        <li>Setting 'softwire-num-max' to an arbitrary high value, which may
          be exploited by a misbehaving user to perform a DoS on the binding
          BR by mounting a massive number of softwires.</t>

          <t>Setting softwires.</li>
        <li>Setting 'icmpv4-rate' or 'icmpv6-rate' to a low value, which may
          lead to the deactivation of ICMP messages handling.</t>

          <t>Accessing to private data maintained by the BR (e.g., the binding
          table or the algorithm configuration). Such data can be misused to
          track the activity of a host.</t>

          <t>Instructing handling.</li>
        <li>Instructing the BR to install entries which entries, which, in turn turn, will induce a
          DDoS attack by means of the notifications generated by the BR. This
          DDoS can be softened by defining a notification interval, but given
          that this interval parameter can be disabled or set to a low value
          by the misbehaving entity, the same problem will be observed.</t>
        </list></t> observed.</li>
      </ul>

      <t>   Some of the readable data nodes in this 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 subtrees and data nodes can be misused
      to track the activity of a host:</t>
      <ul spacing="normal"><li>the binding Table
      (/br-instances/binding/bind-instance/binding-table) </li>
      <li>the algorithm configuration (/br-instances/algorithm/algo-instance/)
      </li></ul>
      <t>Security considerations related to lw4o6, MAP-T, and MAP-E are
      discussed in <xref target="RFC7596"></xref>, target="RFC7596" format="default"/>, <xref target="RFC7597"> target="RFC7597" format="default">
        </xref>, and <xref target="RFC7599"></xref> target="RFC7599" format="default"/> respectively.</t>
      <t>Security considerations given in <xref target="RFC7950"></xref> target="RFC7950" format="default"/> are
      also applicable here.</t>
    </section>
    <section anchor="iana" title="IANA Considerations">
      <t>This document requests IANA to assign a numbered="true" toc="default">
      <name>IANA Considerations</name>
      <t>IANA has assigned the following new tunnel type under the
      "tunnelType" sub-registry
      tunnelType subregistry of the "ifType definitions" Definitions" registry
      maintained at <xref target="TUNNELTYPE-IANA-REGISTRY"></xref> and use
      the following data for in the new entry:</t>

      <figure>
        <artwork align="left"><![CDATA[       Decimal:           TDB1
       Name:              aplusp
       Description:       A+P encapsulation
       Reference:         [RFC6346]
]]></artwork>
      </figure>

      <t>This document requests IANA to register SMI Numbers registry <xref target="TUNNELTYPE-IANA-REGISTRY" format="default"/>:</t>
<ul empty="true"><li>
<dl newline="false" indent="14" spacing="compact">
<dt>Decimal:</dt><dd>18</dd>
<dt>Name:</dt><dd>aplusp</dd>
<dt>Description:</dt><dd>A+P encapsulation</dd>
<dt>Reference:</dt><dd>[RFC6346]</dd>
</dl>
</li></ul>
      <t>IANA has registered the following in the "ns"
      subregistry within the "IETF XML Registry" <xref
      target="RFC3688"></xref>: <figure>
          <artwork><![CDATA[         URI: urn:ietf:params:xml:ns:yang:ietf-softwire-ce
         Registrant Contact: The IESG.
         XML: N/A; target="RFC3688" format="default"/>:

</t>
<ul empty="true"><li>
<dl newline="false" spacing="compact">
<dt>URI:</dt><dd>urn:ietf:params:xml:ns:yang:ietf-softwire-ce</dd>
<dt>Registrant Contact:</dt><dd>The IESG.</dd>
<dt>XML:</dt><dd>N/A; the requested URI is an XML namespace.

         URI: urn:ietf:params:xml:ns:yang:ietf-softwire-br
         Registrant Contact: The IESG.
         XML: N/A; namespace.</dd>
</dl>
</li></ul>

<ul empty="true"><li>
<dl newline="false" spacing="compact">
<dt>URI:</dt><dd>urn:ietf:params:xml:ns:yang:ietf-softwire-br</dd>
<dt>Registrant Contact:</dt><dd>The IESG.</dd>
<dt>XML:</dt><dd>N/A; the requested URI is an XML namespace.

         URI: urn:ietf:params:xml:ns:yang:ietf-softwire-common
         Registrant Contact: The IESG.
         XML: N/A; namespace.</dd>
</dl></li></ul>

<ul empty="true"><li>
<dl newline="false" spacing="compact">
<dt>URI:</dt><dd>urn:ietf:params:xml:ns:yang:ietf-softwire-common</dd>
<dt>Registrant Contact:</dt><dd>The IESG.</dd>
<dt>XML:</dt><dd>N/A; the requested URI is an XML namespace.          ]]></artwork>
        </figure></t>

      <t>This document requests that IANA registers namespace.</dd>
</dl></li></ul>
      <t>IANA has registered the following YANG modules
      in the "YANG Module Names" subregistry <xref target="RFC7950"></xref> target="RFC6020" format="default"/>
      within the "YANG Parameters" registry.<figure>
          <artwork><![CDATA[         name: ietf-softwire-ce
         namespace: urn:ietf:params:xml:ns:yang:ietf-softwire-ce
         prefix: softwire-ce
         reference: RFC XXXX

         name: ietf-softwire-br
         namespace: urn:ietf:params:xml:ns:yang:ietf-softwire-br
         prefix: softwire-br
         reference: RFC XXXX

         name: ietf-softwire-common
         namespace: urn:ietf:params:xml:ns:yang:ietf-softwire-common
         prefix: softwire-common
         reference: RFC XXXX          ]]></artwork>
        </figure></t>
    </section>

    <section anchor="acknowledgements" title="Acknowledgements">
      <t>The authors would like to thank Lishan Li, Bert Wijnen, Giles Heron,
      Ole Troan, Andy Wingo and Leo Tietz for their contributions to this
      work.</t>

      <t>Thanks to Sheng Jiang for the review.</t>

      <t>Special thanks to Tom Petch and Martin Bjorklund for the detailed
      review and suggestions.</t>
    </section>

    <section title="Contributing Authors">
      <t>The following individuals are co-authors:<figure>
          <artwork><![CDATA[   Yong Cui
   Tsinghua University
   Beijing  100084
   P.R. China
   Phone: +86-10-6260-3059
   Email: cuiyong@tsinghua.edu.cn

   Qi Sun
   Tsinghua University
   Beijing  100084
   P.R. China
   Phone: +86-10-6278-5822
   Email: sunqi.ietf@gmail.com

   Linhui Sun
   Tsinghua University
   Beijing  100084
   P.R. China
   Phone: +86-10-6278-5822
   Email: lh.sunlinh@gmail.com

   Sladjana Zechlin
   Deutsche Telekom AG
   Landgrabenweg 151
   Bonn, NRW  53227
   Germany
   Email: sladjana.zechlin@telekom.de

   Rajiv Asati
   Cisco Systems, Inc.
   7025 Kit Creek Rd.
   RTP, NC  27709
   USA
   Email: Rajiva@cisco.com]]></artwork>
        </figure></t>

      <t></t>

      <t></t>
    </section>

    <section anchor="contributors" title="Contributors">
      <t>The following individual contributed to this document:</t>

      <figure>
        <artwork><![CDATA[  Hao Wang
  Tsinghua University
  Beijing 100084
  P.R.China
  Phone: +86-10-6278-5822
  Email: wangh13@mails.tsinghua.edu.cn
        ]]></artwork>
      </figure> registry.</t>
<ul empty="true"><li>
<dl newline="false" spacing="compact">
<dt>name:</dt><dd>ietf-softwire-ce</dd>
<dt>namespace:</dt><dd>urn:ietf:params:xml:ns:yang:ietf-softwire-ce</dd>
<dt>prefix:</dt><dd>softwire-ce</dd>
<dt>reference:</dt><dd>RFC 8676</dd>
</dl></li></ul>

<ul empty="true"><li>
<dl newline="false" spacing="compact">
         <dt>name:</dt><dd>ietf-softwire-br</dd>
         <dt>namespace:</dt><dd>urn:ietf:params:xml:ns:yang:ietf-softwire-br</dd>
         <dt>prefix:</dt><dd>softwire-br</dd>
         <dt>reference:</dt><dd>RFC 8676</dd>
</dl></li></ul>
<ul empty="true"><li>
<dl newline="false" spacing="compact">
         <dt>name:</dt><dd>ietf-softwire-common</dd>
         <dt>namespace:</dt><dd>urn:ietf:params:xml:ns:yang:ietf-softwire-common</dd>
         <dt>prefix:</dt><dd>softwire-common</dd>
         <dt>reference:</dt><dd>RFC 8676</dd>
</dl></li></ul>
    </section>
  </middle>
  <back>
    <references title="Normative References">
      <?rfc include='reference.RFC.3688'?>

      <?rfc include='reference.RFC.8446'?>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.3688.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8446.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6241.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6242.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8341.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8343.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7596.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7597.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7598.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7599.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7950.xml"/>
        <xi:include
	    href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8040.xml"/>

        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6020.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6991.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7224.xml"/>
        <!--      <?rfc include='reference.RFC.6241'?>

      <?rfc include='reference.RFC.6242'?>

      <?rfc include='reference.RFC.8341'?>

      <?rfc include='reference.RFC.8343'?>

      <?rfc include='reference.RFC.7596'?>

      <?rfc include='reference.RFC.7597'?>

      <?rfc include='reference.RFC.7598'?>

      <?rfc include='reference.RFC.7599'?>

      <?rfc include='reference.RFC.7950'?>

      <?rfc include='reference.RFC.8040'?>

      <?rfc include='reference.RFC.6020'?>

      <?rfc include='reference.RFC.6991'?>

      <?rfc include='reference.RFC.7224'?>

      <?rfc include='reference.I-D.ietf-softwire-iftunnel'?> include='reference.I-D.ietf-softwire-iftunnel'?>; companion document -->
<reference anchor="TUNNELTYPE-IANA-REGISTRY"
                 target="https://www.iana.org/assignments/smi-numbers/smi-numbers.xhtml#smi-numbers-6"> anchor='RFC8675' target='https://www.rfc-editor.org/info/rfc8675'>
<front>
          <title>tunnelType Definitions</title>

          <author>
<title>A YANG Data Model for Tunnel Interface Types</title>

<author initials='M' surname='Boucadair' fullname='Mohamed Boucadair'>
    <organization abbrev="IANA">Internet Assigned Numbers
            Authority</organization> />
</author>

<author initials='I' surname='Farrer' fullname='Ian Farrer'>
    <organization />
</author>

<author initials='R' surname='Asati' fullname='Rajiv Asati'>
    <organization />
</author>

<date month='November' year='2019' />
</front>

<seriesInfo name='RFC' value='8675' />
<seriesInfo name="DOI" value="10.17487/RFC8675"/>
</reference>

        <reference anchor="TUNNELTYPE-IANA-REGISTRY" target="https://www.iana.org/assignments/smi-numbers">
          <front>
            <title>Structure of Management Information (SMI) Numbers (MIB
	    Module Registrations)</title>
            <author>
              <organization>IANA</organization>
            </author>
          </front>
        </reference>
      </references>

    <references title="Informative References">
      <?rfc include='reference.RFC.8344'?>

      <?rfc include='reference.RFC.6346'?>

      <?rfc include='reference.RFC.8342'?>

      <?rfc include='reference.RFC.8349'?>

      <?rfc include='reference.RFC.8340'?>

      <?rfc include='reference.RFC.7422'?>

      <?rfc include='reference.RFC.6333'?>

      <?rfc include='reference.RFC.4213'?>

      <?rfc include='reference.RFC.8513'?>

      <?rfc include='reference.RFC.8512'?>
      <references>
        <name>Informative References</name>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8344.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6346.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8342.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8349.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8340.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7422.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6333.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4213.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8513.xml"/>
        <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8512.xml"/>
      </references>
    </references>
    <section anchor="examples" title="Configuration Examples"> numbered="true" toc="default">
      <name>Configuration Examples</name>
      <t>The following sections provide examples of how the softwire YANG
      modules can be used for configuring softwire elements.</t>
      <section anchor="lw4o6-example"
               title="Configuration numbered="true" toc="default">
        <name>Configuration Example for a lw4o6 BR Binding-Table"> Binding-Table</name>
        <t>The lwAFTR maintains an address binding table which that contains the
        following 3-tuples:</t>

        <t><list style="symbols">
            <t>IPv6
        <ul spacing="normal">
          <li>IPv6 Address for a single lwB4</t>

            <t>Public lwB4</li>
          <li>Public IPv4 Address</t>

            <t>Restricted port-set</t>
          </list></t> Address</li>
          <li>Restricted port-set</li>
        </ul>
        <t>The entry has two functions: the IPv6 encapsulation of inbound IPv4
        packets destined to the lwB4 and the validation of outbound
        IPv4-in-IPv6 packets received from the lwB4 for de-capsulation.</t> decapsulation.</t>
        <t>Consider an example for the following lw4o6 binding table
        entry:</t>

        <t><list hangIndent="28" style="hanging">
            <t hangText="lwB4
        <dl newline="false" spacing="normal" indent="28">
          <dt>lwB4 Binding IPv6 Address:">2001:db8::1</t>

            <t hangText="lwB4 Address:</dt>
          <dd>2001:db8::1</dd>
          <dt>lwB4 Binding IPv4 Address:">192.0.2.1</t>

            <t hangText="lwB4 PSID:">0x34</t>

            <t hangText="lwB4 Address:</dt>
          <dd>192.0.2.1</dd>
          <dt>lwB4 PSID:</dt>
          <dd>0x34</dd>
          <dt>lwB4 PSID Length">8</t>

            <t hangText="BR IPv6 Address:">2001:db8:1::2</t>
          </list></t> Length</dt>
          <dd>8</dd>
          <dt>BR IPv6 Address:</dt>
          <dd>2001:db8:1::2</dd>
        </dl>
        <figure anchor="lw4o6-br-example-xml"
                title="lw4o6 Binding-Table anchor="lw4o6-br-example-xml">
          <name>lw4o6 Binding Table Configuration XML">
          <artwork><![CDATA[ XML</name>

          <sourcecode name="" type="xml"><![CDATA[    <br-instances>
      <binding>
          <bind-instance>
            <name>mybinding-instance</name>
            <binding-table>
              <binding-entry>
                <binding-ipv6info>2001:db8::1</binding-ipv6info>
                <binding-ipv4-addr>192.0.2.1</binding-ipv4-addr>
                <port-set>
                  <psid>52</psid>
                  <psid-len>8</psid-len>
                </port-set>
                <br-ipv6-addr>2001:db8:1::2</br-ipv6-addr>
              </binding-entry>
            </binding-table>
            <softwire-num-max>1024</softwire-num-max>
            <softwire-path-mru>1540</softwire-path-mru>
            <softwire-payload-mtu>1500</softwire-payload-mtu>
          </bind-instance>
      </binding>
    </br-instances> ]]></artwork> ]]></sourcecode>
        </figure>
      </section>
      <section anchor="map-e-example"
               title="Configuration numbered="true" toc="default">
        <name>Configuration Example for a MAP-E BR"> BR</name>
        <t>A MAP-E BR is configured with forward mapping rules for the CEs it
        is serving. In this example (taken from <xref
        target="RFC7597"></xref>, target="RFC7597" format="default"/>, Appendix A, Example 2), the following
        parameters are required:</t>

        <t><list style="symbols">
            <t>Rule
        <ul spacing="normal">
          <li>Rule IPv6 Prefix</t>

            <t>Rule Prefix</li>
          <li>Rule IPv4 Prefix</t>

            <t>Rule Prefix</li>
          <li>Rule EA-bit bit length</t>

            <t>IPv6 length</li>
          <li>IPv6 Address of MAP-BR</t>
          </list></t> MAP-BR</li>
        </ul>
        <t>The mapping rule has two functions: identifying the destination CE
        IPv6 address for encapsulating inbound IPv4 packets and the validation
        of outbound IPv4-in-IPv6 packets received from the CE for
        de-capsulation.</t>
        <t>The transport type for the data plane also needs to be configured
        for encapsulation to enable MAP-E and forwarding needs to be
        enabled.</t>
        <t>Consider an example for the following MAP-E Forwarding Mapping
        Rule:</t>

        <t><list hangIndent="20" style="hanging">
            <t hangText="Data plane:">encapsulation</t>

            <t hangText="Rule IPv6 Prefix:">2001:db8::/40</t>

            <t hangText="Rule IPv4 Prefix:">192.0.2.0/24</t>

            <t hangText="Rule
        <dl newline="false" spacing="normal" indent="20">
          <dt>Data plane:</dt>
          <dd>encapsulation</dd>
          <dt>Rule IPv6 Prefix:</dt>
          <dd>2001:db8::/40</dd>
          <dt>Rule IPv4 Prefix:</dt>
          <dd>192.0.2.0/24</dd>
          <dt>Rule EA-bit Length:">16</t>

            <t hangText="BR IPv6 Address:">2001:db8:ffff::1</t>
          </list></t> Length:</dt>
          <dd>16</dd>
          <dt>BR IPv6 Address:</dt>
          <dd>2001:db8:ffff::1</dd>
        </dl>
        <t><xref target="map-e-example-xml"></xref> target="map-e-example-xml" format="default"/> provides the example MAP-E
        BR configuration xml.</t>
        <figure anchor="map-e-example-xml" title="MAP-E anchor="map-e-example-xml">
          <name>MAP-E FMR Configuration XML">
          <artwork><![CDATA[ XML</name>
          <sourcecode name="" type="xml"><![CDATA[    <br-instances>
      <algorithm>
        <algo-instance>
          <name>myalgo-instance</name>
          <encapsulation>
            <br-ipv6-addr>2001:db8:ffff::1</br-ipv6-addr>
          </encapsulation>
          <ea-len>16</ea-len>
          <rule-ipv4-prefix>192.0.2.0/24</rule-ipv4-prefix>
          <rule-ipv6-prefix>2001:db8::/40</rule-ipv6-prefix>
          <forwarding>true</forwarding>
          <port-set>
            <psid-offset>6</psid-offset>
            <psid-len>8</psid-len>
          </port-set>
        </algo-instance>
      </algorithm>
    </br-instances>       ]]></artwork>       ]]></sourcecode>
        </figure>
      </section>
      <section anchor="lw4o6-ce-example"
               title="lw4o6 numbered="true" toc="default">
        <name>lw4o6 CE Configuration Example"> Example</name>
        <t>This section provides XML examples for configuring a lw4o6 CE.
        Examples for routing and NAT44 are also provided for convienience.</t> convenience.</t>
        <t>Consider an example for the following lw4o6 CE configuration:</t>

        <t><list hangIndent="28" style="hanging">
            <t hangText="lwB4
        <dl newline="false" spacing="normal" indent="28">
          <dt>lwB4 Binding IPv6 Address:">2001:db8::1</t>

            <t hangText="lwB4 Address:</dt>
          <dd>2001:db8::1</dd>
          <dt>lwB4 Binding IPv4 Address:">192.0.2.1</t>

            <t hangText="lwB4 PSID:">0x34</t>

            <t hangText="lwB4 Address:</dt>
          <dd>192.0.2.1</dd>
          <dt>lwB4 PSID:</dt>
          <dd>0x34</dd>
          <dt>lwB4 PSID Length">8</t>

            <t hangText="BR IPv6 Address:">2001:db8:1::2</t>
          </list></t> Length</dt>
          <dd>8</dd>
          <dt>BR IPv6 Address:</dt>
          <dd>2001:db8:1::2</dd>
        </dl>
        <figure anchor="lw4o6-ce-example-xml"
                title="lw4o6 anchor="lw4o6-ce-example-xml">
          <name>lw4o6 CE Configuration XML">
          <artwork><![CDATA[ XML</name>
          <sourcecode name="" type="xml"><![CDATA[
<config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <interfaces xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces">
    <interface>
      <name>lw4o6-wan</name>
      <type>iana-tunnel-type:aplusp</type>
      <br-ipv6-addr
        xmlns="urn:ietf:params:xml:ns:yang:ietf-softwire-ce">
        2001:db8:1::2
      </br-ipv6-addr>
      <binding-ipv6info
        xmlns="urn:ietf:params:xml:ns:yang:ietf-softwire-ce">
        2001:db8::1
      </binding-ipv6info>
    </interface>
  </interfaces>
</config>
    ]]></artwork>
    ]]></sourcecode>
        </figure>
        <t>In the example depicted in <xref
        target="lw4o6-ce-example-xml"></xref>, target="lw4o6-ce-example-xml" format="default"/>, the interface name is defined
        for the softwire tunnel. This name is then referenced by the routing
        configuration for the IPv4 route. <xref
        target="lw4o6-ce-routing-example-xml"></xref> target="lw4o6-ce-routing-example-xml" format="default"/> provides an example
        configuration for the CE's IPv4 routing, routing using the YANG module
        described in <xref target="RFC8349"></xref>.</t> target="RFC8349" format="default"/>.</t>
        <figure anchor="lw4o6-ce-routing-example-xml"
                title="lw4o6 anchor="lw4o6-ce-routing-example-xml">
          <name>lw4o6 CE Routing Configuration XML">
          <artwork><![CDATA[ XML</name>
          <sourcecode name="" type="xml"><![CDATA[
<config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <routing xmlns="urn:ietf:params:xml:ns:yang:ietf-routing">
    <control-plane-protocols>
      <control-plane-protocol>
        <type>static</type>
        <name>v4</name>
        <static-routes>
          <ipv4
          xmlns="urn:ietf:params:xml:ns:yang:ietf-ipv4-unicast-routing">
            <route>
              <destination-prefix>0.0.0.0/0</destination-prefix>
              <next-hop>
                <outgoing-interface>lw4o6-wan</outgoing-interface>
              </next-hop>
            </route>
          </ipv4>
        </static-routes>
      </control-plane-protocol>
    </control-plane-protocols>
  </routing>
</config>
    ]]></artwork>
    ]]></sourcecode>
        </figure>
        <t><xref target="lw4o6-ce-nat-example-xml"></xref> target="lw4o6-ce-nat-example-xml" format="default"/> provides an example
        configuration for the CE's NAPT44 function, function using the YANG module
        described in <xref target="RFC8512"></xref>.</t> target="RFC8512" format="default"/>.</t>
        <figure anchor="lw4o6-ce-nat-example-xml"
                title="lw4o6 anchor="lw4o6-ce-nat-example-xml">
          <name>lw4o6 NAT Configuration XML">
          <artwork><![CDATA[ XML</name>
          <sourcecode name="" type="xml"><![CDATA[
<config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <nat xmlns="urn:ietf:params:xml:ns:yang:ietf-nat">
   <instances>
     <instance>
       <id>1</id>
       <policy>
        <policy-id>1</policy-id>
        <external-ip-address-pool>
          <pool-id>1</pool-id>
          <external-ip-pool>192.0.2.1</external-ip-pool>
        </external-ip-address-pool>
        <port-set-restrict>
          <port-set-algo>
            <psid-offset>6</psid-offset>
            <psid-len>8</psid-len>
            <psid>52</psid>
          </port-set-algo>
        </port-set-restrict>
        <notify-pool-usage>
          <pool-id>1</pool-id>
          <high-threshold>80</high-threshold>
        </notify-pool-usage>
        </policy>
        <mapping-limits>
         <limit-per-protocol>
          <protocol-id>1</protocol-id>
          <limit>8</limit>
         </limit-per-protocol>
         <limit-per-protocol>
          <protocol-id>6</protocol-id>
          <limit>32</limit>
         </limit-per-protocol>
         <limit-per-protocol>
          <protocol-id>17</protocol-id>
          <limit>16</limit>
         </limit-per-protocol>
        </mapping-limits>
        <mapping-table>
          <mapping-entry>
            <index>1</index>
            <external-src-address>192.0.2.1/32</external-src-address>
            <internal-src-address>192.168.1.0/24</internal-src-address>
            <transport-protocol>6</transport-protocol>
          </mapping-entry>
          <mapping-entry>
            <index>2</index>
            <external-src-address>192.0.2.1/32</external-src-address>
            <internal-src-address>192.168.1.0/24</internal-src-address>
            <transport-protocol>17</transport-protocol>
          </mapping-entry>
          <mapping-entry>
            <index>3</index>
            <external-src-address>192.0.2.1/32</external-src-address>
            <internal-src-address>192.168.1.0/24</internal-src-address>
            <transport-protocol>1</transport-protocol>
          </mapping-entry>
        </mapping-table>
      </instance>
    </instances>
  </nat>
</config>
]]></artwork>
]]></sourcecode>
        </figure>
      </section>
    </section>

    <section anchor="acknowledgements" numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t>The authors would like to thank Lishan Li, Bert Wijnen, Giles Heron,
      Ole Troan, Andy Wingo, and Leo Tietz for their contributions to this
      work.</t>
      <t>Thanks to Sheng Jiang for the review.</t>
      <t>Special thanks to Tom Petch and Martin Bjorklund for the detailed
      review and suggestions.</t>
    </section>

    <section numbered="false" toc="default">
      <name>Contributors</name>
      <t>The following individuals are co-authors:</t>
      <artwork name="" type="" align="left" alt=""><![CDATA[   Yong Cui
   Tsinghua University
   China
   Phone: +86-10-6260-3059
   Email: cuiyong@tsinghua.edu.cn
]]></artwork>

<artwork name="" type="" align="left" alt=""><![CDATA[
   Qi Sun
   Tsinghua University
   China
   Phone: +86-10-6278-5822
   Email: sunqi.ietf@gmail.com
]]></artwork>
<artwork name="" type="" align="left" alt=""><![CDATA[
   Linhui Sun
   Tsinghua University
   China
   Phone: +86-10-6278-5822
   Email: lh.sunlinh@gmail.com
]]></artwork>
<artwork name="" type="" align="left" alt=""><![CDATA[
   Sladjana Zechlin
   Deutsche Telekom AG
   Germany
   Email: sladjana.zechlin@telekom.de
]]></artwork>
<artwork name="" type="" align="left" alt=""><![CDATA[
   Rajiv Asati
   Cisco Systems, Inc.
   United States of America
   Email: Rajiva@cisco.com]]></artwork>

<artwork name="" type="" align="left" alt=""><![CDATA[
   Hao Wang
   Tsinghua University
   China
   Phone: +86-10-6278-5822
   Email: wangh13@mails.tsinghua.edu.cn]]></artwork>
    </section>
  </back>
</rfc>