    Internet Engineering Task Force (IETF)                      M. Boucadair
    Request for Comments: 8513                                  C. Jacquenet
    Category: Standards Track                                         Orange
    ISSN: 2070-1721                                             S. Sivakumar
                                                               Cisco Systems
                                                                January 2019

                A YANG Data Model for Dual-Stack Lite (DS-Lite)

    Abstract

       This document defines a YANG module for the Dual-Stack Lite (DS-Lite)
       Address Family Transition Router (AFTR) and Basic Bridging BroadBand
       (B4) elements.

    Status of This Memo

       This is an Internet Standards Track document.

       This document is a product of the Internet Engineering Task Force
       (IETF).  It represents the consensus of the IETF community.  It has
       received public review and has been approved for publication by the
       Internet Engineering Steering Group (IESG).  Further information on
       Internet Standards is available in Section 2 of RFC 7841.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       https://www.rfc-editor.org/info/rfc8513.

    Copyright Notice

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

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

    Boucadair, et al.            Standards Track                    [Page 1]

    RFC 8513                   DS-Lite YANG Module              January 2019

    Table of Contents

       1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
         1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
       2.  DS-Lite YANG Module: An Overview  . . . . . . . . . . . . . .   4
       3.  DS-Lite YANG Module . . . . . . . . . . . . . . . . . . . . .   7
       4.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
       5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
       6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
         6.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
         6.2.  Informative References  . . . . . . . . . . . . . . . . .  17
       Appendix A.  B4 Example . . . . . . . . . . . . . . . . . . . . .  19
       Appendix B.  AFTR Examples  . . . . . . . . . . . . . . . . . . .  19
       Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  21
       Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

    1.  Introduction

       This document defines a data model for DS-Lite [RFC6333], using the
       YANG data modeling language [RFC7950].  Both the Address Family
       Transition Router (AFTR) and Basic Bridging BroadBand (B4) elements
       are covered by this specification.

       Figure 1 is a slight adaptation of Figure 1 from RFC 6333 and is
       provided here for the convenience of the reader.

    Boucadair, et al.            Standards Track                    [Page 2]

    RFC 8513                   DS-Lite YANG Module              January 2019

                          +-----------+
                          |    Host   |
                          +-----+-----+
                                |192.0.2.1
                                |
                                |
                                |192.0.2.2
                      +---------|---------+
                      |         |         |
                      |    Home router    |
                      |+--------+--------+|
                      ||       B4        ||
                      |+--------+--------+|
                      +--------|||--------+
                               |||2001:db8:0:1::1
                               |||
                               |||<-IPv4-in-IPv6 Softwire
                               |||
                        -------|||-------
                      /        |||        \
                     |   ISP core network  |
                      \        |||        /
                        -------|||-------
                               |||
                               |||2001:db8:0:2::1
                      +--------|||--------+
                      |        AFTR       |
                      |+--------+--------+|
                      ||   Concentrator  ||
                      |+--------+--------+|
                      |       |NAT|       |
                      |       +-+-+       |
                      +---------|---------+
                                |198.51.100.1
                                |
                        --------|--------
                      /         |         \
                     |       Internet      |
                      \         |         /
                        --------|--------
                                |
                                |203.0.113.1
                          +-----+-----+
                          | IPv4 Host |
                          +-----------+

                        Figure 1: DS-Lite Base Architecture

    Boucadair, et al.            Standards Track                    [Page 3]

    RFC 8513                   DS-Lite YANG Module              January 2019

       DS-Lite deployment considerations are discussed in [RFC6908].

       This document follows the guidelines of [RFC8407], uses the common
       YANG types defined in [RFC6991], and adopts the Network Management
       Datastore Architecture (NMDA) [RFC8342].

    1.1.  Terminology

       This document makes use of the terms defined in Section 3 of
       [RFC6333].

       The terminology for describing YANG data models is defined in
       [RFC7950].

       The meaning of the symbols in tree diagrams is defined in [RFC8340].

    2.  DS-Lite YANG Module: An Overview

       As shown in Figure 1:

       o  The AFTR element is a combination of an IPv4-in-IPv6 tunnel and a
          NAPT function (Section 2.2 of [RFC3022]).

       o  The B4 element is an IPv4-in-IPv6 tunnel.

       Therefore, the DS-Lite YANG module is designed to augment both the
       Interfaces YANG module [RFC8343] and the NAT YANG module [RFC8512]
       with DS-Lite-specific features.

       The YANG "feature" statement is used to distinguish which of the
       DS-Lite elements ('aftr' or 'b4') is relevant for a specific data
       node.

       Concretely, the DS-Lite YANG module (Figure 2) augments the
       Interfaces YANG module with the following:

       o  An IPv6 address used by the tunnel endpoint (AFTR or B4) for
          sending and receiving IPv4-in-IPv6 packets (ipv6-address).

       o  An IPv4 address that is used by the tunnel endpoint (AFTR or B4)
          for troubleshooting purposes (ipv4-address).

       o  An IPv6 address used by a B4 element to reach its AFTR (aftr-
          ipv6-addr).

       o  The tunnel MTU used to avoid fragmentation (tunnel-mtu).

    Boucadair, et al.            Standards Track                    [Page 4]

    RFC 8513                   DS-Lite YANG Module              January 2019

       o  A policy to instruct the tunnel endpoint (AFTR or B4) whether it
          must preserve Differentiated Services Code Point (DSCP) marking
          when encapsulating/decapsulating packets (v6-v4-dscp-
          preservation).

       In addition, the DS-Lite YANG module augments the NAT YANG module
       (policy, in particular) with the following:

       o  A policy to limit the number of DS-Lite softwires per subscriber
          (max-softwire-per-subscriber).

       o  A policy to instruct the AFTR whether a state can be automatically
          migrated (state-migrate).

       o  Further, in order to prevent a Denial of Service (DoS) by
          frequently changing the source IPv6 address, 'b4-address-change-
          limit' is used to rate-limit such changes.

       o  An instruction to rewrite the TCP Maximum Segment Size (MSS)
          option (mss-clamping) to avoid TCP fragmentation.

       Given that the NAPT table of the AFTR element is extended to include
       the source IPv6 address of incoming packets, the DS-Lite YANG module
       augments the NAPT44 mapping entry with the following:

       o  b4-ipv6-address, which is used to record the source IPv6 address
          of a packet received from a B4 element.  This IPv6 address is
          required to disambiguate between the overlapping IPv4 address
          space of subscribers.

       o  The value of the Traffic Class field in the IPv6 header as
          received from a B4 element (v6-dscp): This information is used to
          preserve DSCP marking when encapsulating/decapsulating at the
          AFTR.

       o  The IPv4 DSCP marking of the IPv4 packet received from a B4
          element (internal-v4-dscp): This information can be used by the
          AFTR for setting the DSCP of packets relayed to a B4 element.

       o  The IPv4 DSCP marking as set by the AFTR in its external interface
          (external-v4-dscp): An AFTR can be instructed to preserve the same
          marking or to set it to another value when forwarding an IPv4
          packet destined to a remote IPv4 host.

       Access Control List (ACL) and Quality-of-Service (QoS) policies
       discussed in Section 2.5 of [RFC6908] are out of scope.  A YANG
       module for ACLs is documented in [ACL-YANG].

    Boucadair, et al.            Standards Track                    [Page 5]

    RFC 8513                   DS-Lite YANG Module              January 2019

       Likewise, considerations that are related to the Port Control
       Protocol (PCP) and discussed in Section 8.5 of [RFC6333] are out of
       scope.  A YANG module for PCP is documented in [YANG-PCP].

       The YANG module "ietf-dslite" has the following structure:

       module: ietf-dslite
         augment /if:interfaces/if:interface:
           +--rw ipv6-address?              inet:ipv6-address
           +--rw ipv4-address?              inet:ipv4-address
           +--rw aftr-ipv6-addr?            inet:ipv6-address {b4}?
           +--rw tunnel-mtu?                uint16
           +--rw v6-v4-dscp-preservation?   boolean
         augment /nat:nat/nat:instances/nat:instance/nat:policy:
           +--rw max-softwires-per-subscriber?   uint8 {aftr}?
           +--rw state-migrate?                  boolean {aftr}?
           +--rw b4-address-change-limit?        uint32 {aftr}?
           +--rw mss-clamping {aftr}?
              +--rw enable?      boolean
              +--rw mss-value?   uint16
         augment /nat:nat/nat:instances/nat:instance
                 /nat:mapping-table/nat:mapping-entry:
           +--rw b4-ipv6-address {aftr}?
           |  +--rw address?               inet:ipv6-address
           |  +--rw last-address-change?   yang:date-and-time
           +--rw v6-dscp?            inet:dscp {aftr}?
           +--rw internal-v4-dscp?   inet:dscp {aftr}?
           +--rw external-v4-dscp?   inet:dscp {aftr}?
         augment /nat:nat/nat:instances/nat:instance
                 /nat:statistics/nat:mappings-statistics:
           +--ro active-softwires?   yang:gauge32 {aftr}?

         notifications:
           +---n b4-address-change-limit-policy-violation {aftr}?
              +--ro id           -> /nat:nat/instances/instance/id
              +--ro policy-id    -> /nat:nat/instances/instance/policy/id
              +--ro address      inet:ipv6-address

                        Figure 2: DS-Lite YANG Tree Diagram

       Examples to illustrate the use of the "ietf-dslite" module are
       provided in Appendices A and B.

    Boucadair, et al.            Standards Track                    [Page 6]

    RFC 8513                   DS-Lite YANG Module              January 2019

    3.  DS-Lite YANG Module

       This module uses the tunnel interface identity defined in [RFC7224].

      <CODE BEGINS> file "ietf-dslite@2019-01-10.yang"

      module ietf-dslite {
       yang-version 1.1;
       namespace "urn:ietf:params:xml:ns:yang:ietf-dslite";
       prefix dslite;

       import ietf-inet-types {
         prefix inet;
         reference
           "Section 4 of RFC 6991";
       }
       import ietf-interfaces {
         prefix if;
         reference
           "RFC 8343: A YANG Data Model for Interface Management";
       }
       import iana-if-type {
         prefix ianaift;
         reference
           "RFC 7224: IANA Interface Type YANG Module";
       }
       import ietf-nat {
         prefix nat;
         reference
           "RFC 8512: A YANG Module for Network Address Translation (NAT)
                      and Network Prefix Translation (NPT)";
       }
       import ietf-yang-types {
         prefix yang;
         reference
           "Section 3 of RFC 6991";
       }

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

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

    Boucadair, et al.            Standards Track                    [Page 7]

    RFC 8513                   DS-Lite YANG Module              January 2019

          Author:  Christian Jacquenet
                   <mailto:christian.jacquenet@orange.com>

          Author:  Senthil Sivakumar
                   <mailto:ssenthil@cisco.com>";

       description
         "This module is a YANG module for DS-Lite AFTR and B4
          implementations.

          Copyright (c) 2018 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 8513; see
          the RFC itself for full legal notices.";

       revision 2019-01-10 {
         description
           "Initial revision.";
         reference
           "RFC 8513: A YANG Data Model for Dual-Stack Lite (DS-Lite)";
       }

       identity dslite {
         base ianaift:tunnel;
         description
           "DS-Lite tunnel.";
       }

       /*
        * Features
        */

       feature b4 {
         description
           "The B4 element is a function implemented on a dual-stack-capable
            node, either a directly connected device or Customer Premises
            Equipment (CPE), that creates a tunnel to an AFTR.";
         reference
           "Section 5 of RFC 6333";
       }

    Boucadair, et al.            Standards Track                    [Page 8]

    RFC 8513                   DS-Lite YANG Module              January 2019

       feature aftr {
         description
           "An AFTR element is the combination of an IPv4-in-IPv6 tunnel
            endpoint and an IPv4-IPv4 NAT implemented on the same node.";
         reference
           "Section 6 of RFC 6333";
       }

       /*
        * Augments
        */

       augment "/if:interfaces/if:interface" {
         when 'derived-from(if:type, "dslite")';
         description
           "Augments Interface module with DS-Lite parameters.

            IANA interface types are maintained at this registry:
            <https://www.iana.org/assignments/ianaiftype-mib/>.

            tunnel (131),       -- Encapsulation interface";
         leaf ipv6-address {
           type inet:ipv6-address;
           description
             "IPv6 address of the local DS-Lite endpoint (AFTR or B4).";
           reference
             "RFC 6333: Dual-Stack Lite Broadband Deployments Following
                        IPv4 Exhaustion";
         }
         leaf ipv4-address {
           type inet:ipv4-address;
           description
             "IPv4 address of the local DS-Lite AFTR or B4.

              192.0.0.1 is reserved for the AFTR element, while
              192.0.0.0/29 is reserved for the B4 element.

              This address can be used to report ICMP problems and will
              appear in traceroute outputs.";
           reference
             "RFC 6333: Dual-Stack Lite Broadband Deployments Following
                        IPv4 Exhaustion";
         }
         leaf aftr-ipv6-addr {
           if-feature "b4";
           type inet:ipv6-address;
           description
             "Indicates the AFTR's IPv6 address to be used by a B4

    Boucadair, et al.            Standards Track                    [Page 9]

    RFC 8513                   DS-Lite YANG Module              January 2019

              element.";
           reference
             "RFC 6333: Dual-Stack Lite Broadband Deployments Following
                        IPv4 Exhaustion";
         }
         leaf tunnel-mtu {
           type uint16;
           description
             "Configures a tunnel MTU.

              RFC 6908 specifies that since fragmentation and reassembly
              are not optimal, the operator should do everything possible
              to eliminate the need for them.  If the operator uses simple
              IPv4-in-IPv6 softwire, it is recommended that the MTU size
              of the IPv6 network between the B4 and the AFTR account
              for the additional overhead (40 bytes).";
           reference
             "RFC 6908: Deployment Considerations for Dual-Stack Lite";
         }
         leaf v6-v4-dscp-preservation {
           type boolean;
           description
             "Copies the DSCP value from the IPv6 header, and vice versa.

              According to Section 2.10 of RFC 6908, operators should
              use the uniform model by provisioning the network such
              that the AFTR/B4 copies the DSCP value in the IPv4 header
              to the Traffic Class field in the IPv6 header, after the
              IPv4-in-IPv6 encapsulation.";
           reference
             "Section 2.10 of RFC 6908";
         }
       }

       augment "/nat:nat/nat:instances/nat:instance/nat:policy" {
         when "derived-from-or-self(/nat:nat/nat:instances/nat:instance"
            + "/nat:type, 'nat:napt44')"
            + " and /nat:nat/nat:instances/nat:instance/"
            + "nat:per-interface-binding='dslite'";
         if-feature "aftr";
         description
           "Augments the NAPT44 module with AFTR parameters.";
         leaf max-softwires-per-subscriber {
           type uint8;
           default "1";
           description
             "Configures the maximum softwires per subscriber feature.

    Boucadair, et al.            Standards Track                   [Page 10]

    RFC 8513                   DS-Lite YANG Module              January 2019

              A subscriber is uniquely identified by means
              of a subscriber-mask (subscriber-mask-v6).

              This policy aims to prevent a misbehaving subscriber from
              mounting several DS-Lite softwires that would consume
              additional AFTR resources (e.g., get more external ports
              if the quota was enforced on a per-softwire basis and
              consume extra processing due to a large number of active
              softwires).";
           reference
             "Section 4 of RFC 7785";
         }
         leaf state-migrate {
           type boolean;
           default "true";
           description
             "State migration is enabled by default.

              In the event a new IPv6 address is assigned to the B4 element,
              the AFTR should migrate existing state to be bound to the new
              IPv6 address.  This operation ensures that traffic destined to
              the previous B4's IPv6 address will be redirected to the newer
              B4's IPv6 address.  The destination IPv6 address for tunneling
              return traffic from the AFTR should be the last seen as the
              B4's IPv6 source address from the user device (e.g., CPE).

              The AFTR uses the subscriber-mask-v6 to determine whether two
              IPv6 addresses belong to the same CPE (e.g., if the
              subscriber-mask-v6 is set to 56, the AFTR concludes that
              2001:db8:100:100::1 and 2001:db8:100:100::2 belong to the same
              CPE assigned with 2001:db8:100:100::/56).";
           reference
             "RFC 7785: Recommendations for Prefix Binding in the Context
                        of Softwire Dual-Stack Lite";
         }
         leaf b4-address-change-limit {
           type uint32;
           units "seconds";
           default "1800";
           description
             "Minimum number of seconds between a successive B4's IPv6
              address change from the same prefix.

              Changing the source B4's IPv6 address may be used as an attack
              vector.  Packets with a new B4's IPv6 address from the same
              prefix should be rate-limited.

              It is recommended that this rate limit be set to 30 minutes;

    Boucadair, et al.            Standards Track                   [Page 11]

    RFC 8513                   DS-Lite YANG Module              January 2019

              other values can be set on a per-deployment basis.";
           reference
             "RFC 7785: Recommendations for Prefix Binding in the Context
                        of Softwire Dual-Stack Lite";
         }
         container mss-clamping {
           description
             "MSS rewriting configuration to avoid IPv6 fragmentation.";
           leaf enable {
             type boolean;
             description
               "Enable/disable MSS rewriting feature.";
           }
           leaf mss-value {
             type uint16;
             units "octets";
             description
               "Sets the MSS value to be used for MSS rewriting.";
           }
         }
       }

       augment "/nat:nat/nat:instances/nat:instance"
             + "/nat:mapping-table/nat:mapping-entry" {
         when "derived-from-or-self(/nat:nat/nat:instances/nat:instance"
            + "/nat:type, 'nat:napt44')"
            + "and /nat:nat/nat:instances/nat:instance"
            + "/nat:per-interface-binding='dslite'";
         if-feature "aftr";
         description
           "Augments the NAPT44 mapping table with DS-Lite specifics.";
         container b4-ipv6-address {
           description
             "Records the IPv6 address used by a B4 element and the last
              time that address changed.";
           leaf address {
             type inet:ipv6-address;
             description
               "Corresponds to the IPv6 address used by a B4 element.";
             reference
               "RFC 6333: Dual-Stack Lite Broadband Deployments Following
                          IPv4 Exhaustion";
           }
           leaf last-address-change {
             type yang:date-and-time;
             description
               "Records the last time that the address changed.";
           }

    Boucadair, et al.            Standards Track                   [Page 12]

    RFC 8513                   DS-Lite YANG Module              January 2019

         }
         leaf v6-dscp {
           when "/if:interfaces/if:interface"
              + "/dslite:v6-v4-dscp-preservation = 'true'";
           type inet:dscp;
           description
             "DSCP value used at the softwire level (i.e., IPv6 header).";
         }
         leaf internal-v4-dscp {
           when "/if:interfaces/if:interface"
              + "/dslite:v6-v4-dscp-preservation = 'true'";
           type inet:dscp;
           description
             "DSCP value of the encapsulated IPv4 packet.";
         }
         leaf external-v4-dscp {
           when "/if:interfaces/if:interface"
              + "/dslite:v6-v4-dscp-preservation = 'true'";
           type inet:dscp;
           description
             "DSCP value of the translated IPv4 packet as marked by
              the AFTR.";
         }
       }

       augment "/nat:nat/nat:instances/nat:instance"
             + "/nat:statistics/nat:mappings-statistics" {
         if-feature "aftr";
         description
           "Indicates the number of active softwires.";
         leaf active-softwires {
           type yang:gauge32;
           description
             "The number of currently active softwires on the AFTR
              instance.";
         }
       }

       /*
        * Notifications
        */

       notification b4-address-change-limit-policy-violation {
         if-feature "aftr";
         description
           "Generates notifications when a B4 unsuccessfully attempts
            to change the IPv6 address in a time shorter than the value
            of b4-address-change-limit.

    Boucadair, et al.            Standards Track                   [Page 13]

    RFC 8513                   DS-Lite YANG Module              January 2019

            Notifications are rate-limited (notify-interval).";
         leaf id {
           type leafref {
             path "/nat:nat/nat:instances/nat:instance/nat:id";
           }
           mandatory true;
           description
             "NAT instance identifier.";
         }
         leaf policy-id {
           type leafref {
             path "/nat:nat/nat:instances/nat:instance/nat:policy/nat:id";
           }
           mandatory true;
           description
             "Policy identifier.";
         }
         leaf address {
           type inet:ipv6-address;
           mandatory true;
           description
             "B4's IPv6 address.";
         }
       }
      }

      <CODE ENDS>

    Boucadair, et al.            Standards Track                   [Page 14]

    RFC 8513                   DS-Lite YANG Module              January 2019

    4.  Security Considerations

       The YANG module specified in this document defines a schema for data
       that is designed to be accessed via network management protocols such
       as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
       is the secure transport layer, and the mandatory-to-implement secure
       transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
       is HTTPS, and the mandatory-to-implement secure transport is TLS
       [RFC8446].

       The Network Configuration Access Control Model (NACM) [RFC8341]
       provides the means to restrict access for particular NETCONF or
       RESTCONF users to a preconfigured subset of all available NETCONF or
       RESTCONF protocol operations and content.

       All data nodes defined in the YANG module that 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
       network operations.  An attacker who is able to access the B4/AFTR
       can undertake various attacks, such as:

       o  Setting the value of 'aftr-ipv6-addr' on the B4 to point to an
          illegitimate AFTR so that it can intercept all the traffic sent by
          a B4.  Illegitimately intercepting users' traffic is an attack
          with severe implications on privacy.

       o  Setting the MTU to a low value, which may increase the number of
          fragments ('tunnel-mtu' for both B4 and AFTR).

       o  Setting 'max-softwire-per-subscriber' to an arbitrary high value,
          which will be exploited by a misbehaving user to grab more
          resources (by mounting as many softwires as required to get more
          external IP addresses/ports) or to perform a DoS on the AFTR by
          mounting a massive number of softwires.

       o  Setting 'state-migrate' to 'false' on the AFTR.  This action may
          lead to a service degradation for the users.

       o  Setting 'b4-address-change-limit' to an arbitrary low value can
          ease DoS attacks based on frequent change of the B4 IPv6 address.

       o  Setting 'v6-v4-dscp-preservation' to 'false" may lead to a service
          degradation if some policies are applied on the network based on
          the DSCP value.

       Additional security considerations are discussed in [RFC8512].

    Boucadair, et al.            Standards Track                   [Page 15]

    RFC 8513                   DS-Lite YANG Module              January 2019

       Security considerations related to DS-Lite are discussed in
       [RFC6333].

    5.  IANA Considerations

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

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

       IANA has registered the following YANG module in the "YANG Module
       Names" subregistry [RFC7950] within the "YANG Parameters" registry.

                name: ietf-dslite
                namespace: urn:ietf:params:xml:ns:yang:ietf-dslite
                prefix: dslite
                reference: RFC 8513

    6.  References

    6.1.  Normative References

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

       [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
                  and A. Bierman, Ed., "Network Configuration Protocol
                  (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
                  <https://www.rfc-editor.org/info/rfc6241>.

       [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
                  Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
                  <https://www.rfc-editor.org/info/rfc6242>.

       [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
                  Stack Lite Broadband Deployments Following IPv4
                  Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
                  <https://www.rfc-editor.org/info/rfc6333>.

       [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
                  RFC 6991, DOI 10.17487/RFC6991, July 2013,
                  <https://www.rfc-editor.org/info/rfc6991>.

    Boucadair, et al.            Standards Track                   [Page 16]

    RFC 8513                   DS-Lite YANG Module              January 2019

       [RFC7224]  Bjorklund, M., "IANA Interface Type YANG Module",
                  RFC 7224, DOI 10.17487/RFC7224, May 2014,
                  <https://www.rfc-editor.org/info/rfc7224>.

       [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
                  RFC 7950, DOI 10.17487/RFC7950, August 2016,
                  <https://www.rfc-editor.org/info/rfc7950>.

       [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
                  Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
                  <https://www.rfc-editor.org/info/rfc8040>.

       [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
                  Access Control Model", STD 91, RFC 8341,
                  DOI 10.17487/RFC8341, March 2018,
                  <https://www.rfc-editor.org/info/rfc8341>.

       [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
                  Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
                  <https://www.rfc-editor.org/info/rfc8343>.

       [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
                  Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
                  <https://www.rfc-editor.org/info/rfc8446>.

       [RFC8512]  Boucadair, M., Ed., Sivakumar, S., Jacquenet, C.,
                  Vinapamula, S., and Q. Wu, "A YANG Module for Network
                  Address Translation (NAT) and Network Prefix Translation
                  (NPT)", RFC 8512, DOI 10.17487/RFC8512, January 2019,
                  <https://www.rfc-editor.org/info/rfc8512>.

    6.2.  Informative References

       [ACL-YANG] Jethanandani, M., Agarwal, S., Huang, L., and D. Blair,
                  "Network Access Control List (ACL) YANG Data Model", Work
                  in Progress, draft-ietf-netmod-acl-model-21, November
                  2018.

       [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
                  Address Translator (Traditional NAT)", RFC 3022,
                  DOI 10.17487/RFC3022, January 2001,
                  <https://www.rfc-editor.org/info/rfc3022>.

       [RFC6908]  Lee, Y., Maglione, R., Williams, C., Jacquenet, C., and
                  M. Boucadair, "Deployment Considerations for Dual-Stack
                  Lite", RFC 6908, DOI 10.17487/RFC6908, March 2013,
                  <https://www.rfc-editor.org/info/rfc6908>.

    Boucadair, et al.            Standards Track                   [Page 17]

    RFC 8513                   DS-Lite YANG Module              January 2019

       [RFC7785]  Vinapamula, S. and M. Boucadair, "Recommendations for
                  Prefix Binding in the Context of Softwire Dual-Stack
                  Lite", RFC 7785, DOI 10.17487/RFC7785, February 2016,
                  <https://www.rfc-editor.org/info/rfc7785>.

       [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
                  BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
                  <https://www.rfc-editor.org/info/rfc8340>.

       [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
                  and R. Wilton, "Network Management Datastore Architecture
                  (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
                  <https://www.rfc-editor.org/info/rfc8342>.

       [RFC8407]  Bierman, A., "Guidelines for Authors and Reviewers of
                  Documents Containing YANG Data Models", BCP 216, RFC 8407,
                  DOI 10.17487/RFC8407, October 2018,
                  <https://www.rfc-editor.org/info/rfc8407>.

       [YANG-PCP] Boucadair, M., Jacquenet, C., Sivakumar, S., and
                  S. Vinapamula, "YANG Modules for the Port Control Protocol
                  (PCP)", Work in Progress, draft-boucadair-pcp-yang-05,
                  October 2017.

    Boucadair, et al.            Standards Track                   [Page 18]

    RFC 8513                   DS-Lite YANG Module              January 2019

    Appendix A.  B4 Example

       The following example shows a B4 element (2001:db8:0:1::1) that is
       configured with an AFTR element (2001:db8:0:2::1).  The B4 element is
       also instructed to preserve the DSCP marking.

       <interfaces>
         <interface>
           <name>myB4</name>
           <type>dslite:dslite</type>
           <enabled>true</enabled>
           <dslite:ipv6-address>
             2001:db8:0:1::1
           </dslite:ipv6-address>
           <dslite:aftr-ipv6-addr>
             2001:db8:0:2::1
           </dslite:aftr-ipv6-addr>
           <dslite:v6-v4-dscp-preservation>
             true
           </dslite:v6-v4-dscp-preservation>
         </interface>
       </interfaces>

    Appendix B.  AFTR Examples

       The following example shows an AFTR that is reachable at
       2001:db8:0:2::1.  Also, this XML snippet indicates that the AFTR is
       provided with an IPv4 address (192.0.0.1) to be used for
       troubleshooting purposes such as reporting problems to B4s.

       Note that a subscriber is identified by a subscriber-mask [RFC7785]
       that can be configured by means of [RFC8512].

       <interfaces>
         <interface>
           <name>myAFTR</name>
           <type>dslite:dslite</type>
           <enabled>true</enabled>
           <dslite:ipv6-address>2001:db8:0:2::1</dslite:ipv6-address>
           <dslite:ipv4-address>192.0.0.1</dslite:ipv4-address>
         </interface>
       </interfaces>

       The following shows an XML excerpt depicting a dynamic UDP mapping
       entry maintained by a DS-Lite AFTR for a packet received from the B4
       element introduced in Appendix A.  Concretely, this UDP packet
       received with a source IPv6 address (2001:db8:0:1::1), a source IPv4
       address (192.0.2.1), and a source port number (1568) is translated

    Boucadair, et al.            Standards Track                   [Page 19]

    RFC 8513                   DS-Lite YANG Module              January 2019

       into a UDP packet having a source IPv4 address (198.51.100.1) and
       source port number (15000).  The remaining lifetime of this mapping
       is 300 seconds.

       <mapping-entry>
         <index>15</index>
         <type>
           dynamic-explicit
         </type>
         <transport-protocol>
           17
         </transport-protocol>
         <dslite:b4-ipv6-address>
           <dslite:address>
             2001:db8:0:1::1
           </dslite:address>
         </dslite:b4-ipv6-address>
         <internal-src-address>
           192.0.2.1
         </internal-src-address>
         <internal-src-port>
           <start-port-number>
             1568
           </start-port-number>
         </internal-src-port>
         <external-src-address>
           198.51.100.1
         </external-src-address>
         <external-src-port>
           <start-port-number>
             15000
           </start-port-number>
         </external-src-port>
         <lifetime>
           300
         </lifetime>
       </mapping-entry>

    Boucadair, et al.            Standards Track                   [Page 20]

    RFC 8513                   DS-Lite YANG Module              January 2019

    Acknowledgements

       Thanks to Qin Wu, Benoit Claise, and Andy Bierman who helped to
       identify compiling errors.  Mahesh Jethanandani provided early YANG
       Doctors reviews; many thanks to him.

       Many thanks to Ian Farrer and Tom Petch for their reviews and
       comments.

    Authors' Addresses

       Mohamed Boucadair
       Orange
       Rennes  35000
       France

       Email: mohamed.boucadair@orange.com

       Christian Jacquenet
       Orange
       Rennes  35000
       France

       Email: christian.jacquenet@orange.com

       Senthil Sivakumar
       Cisco Systems
       7100-8 Kit Creek Road
       Research Triangle Park, North Carolina  27709
       United States of America

       Phone: +1-919-392-5158
       Email: ssenthil@cisco.com

    Boucadair, et al.            Standards Track                   [Page 21]