Network Working Group                                       M. Boucadair
Internet-Draft                                              C. Jacquenet
Intended status: Standards Track                                  Orange
Expires: February 3, 11, 2018                                  S. Sivakumar
                                                           Cisco Systems
                                                         August 2, 10, 2017

                    YANG Data Models for the DS-Lite
                   draft-ietf-softwire-dslite-yang-04
                   draft-ietf-softwire-dslite-yang-05

Abstract

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

Status of This Memo

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

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

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

   This Internet-Draft will expire on February 3, 11, 2018.

Copyright Notice

   Copyright (c) 2017 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2   4
     1.2.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   2   4
   2.  DS-Lite YANG Data Models  . . . . . . . . . . . . . . . . . .   3   4
   3.  DS-Lite AFTR YANG Module  . . . . . . . . . . . . . . . . . .   4   6
   4.  DS-Lite B4 YANG Module  . . . . . . . . . . . . . . . . . . .  10  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  13  14
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13  15
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14  15
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14  15
     8.1.  Normative references  . . . . . . . . . . . . . . . . . .  14  15
     8.2.  Informative references  . . . . . . . . . . . . . . . . .  15  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16  17

1.  Introduction

   This document defines a data model models for DS-Lite [RFC6333], using the
   YANG data modeling language [RFC6020].  Both the Address Family
   Transition Router (AFTR) and Basic Bridging BroadBand (B4) elements
   are covered by this specification.  As a reminder, Figure 1
   illustrates an overview of the DS-Lite architecture that involves
   AFTR and B4 elements.

                      +-----------+
                      |    Host   |
                      +-----+-----+
                            |10.0.0.1
                            |
                            |
                            |10.0.0.2
                  +---------|---------+
                  |         |         |
                  |    Home router    |
                  |+--------+--------+|
                  ||       B4        ||
                  |+--------+--------+|
                  +--------|||--------+
                           |||2001:db8:0:1::1
                           |||
                           |||<-IPv4-in-IPv6 softwire
                           |||
                    -------|||-------
                  /        |||        \
                 |   ISP core network  |
                  \        |||        /
                    -------|||-------
                           |||
                           |||2001:db8:0:2::1
                  +--------|||--------+
                  |        AFTR       |
                  |+--------+--------+|
                  ||   Concentrator  ||
                  |+--------+--------+|
                  |       |NAT|       |
                  |       +-+-+       |
                  +---------|---------+
                            |192.0.2.1
                            |
                    --------|--------
                  /         |         \
                 |       Internet      |
                  \         |         /
                    --------|--------
                            |
                            |198.51.100.1
                      +-----+-----+
                      | IPv4 Host |
                      +-----------+

                    Figure 1: DS-Lite Base Architecture

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

   This document follows the guidelines of [RFC6087].

   This document [RFC6087], uses the common
   YANG types defined in [RFC6991]. [RFC6991], and adopts Network Management
   Datastore Architecture (NMDA).

1.1.  Terminology

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

   The terminology for describing YANG data models is defined in
   [RFC6020].

1.2.  Tree Diagrams

   The meaning of the symbols in these diagrams is as follows:

   o  Brackets "[" and "]" enclose list keys.

   o  Curly braces "{" and "}" contain names of optional features that
      make the corresponding node conditional.

   o  Abbreviations before data node names: "rw" means configuration
      (read-write), "ro" state data (read-only).

   o  Symbols after data node names: "?" means an optional node, "!" a
      container with presence, and "*" denotes a "list" or "leaf-list".

   o  Parentheses enclose choice and case nodes, and case nodes are also
      marked with a colon (":").

   o  Ellipsis ("...") stands for contents of subtrees that are not
      shown.

2.  DS-Lite YANG Data Models

   Figure 1 2 depicts the YANG data model for the AFTR, AFTR element, while
   Figure 2 3 shows the YANG data model for the B4 element.

   As shown in Figure 1:

   o  The AFTR model supports enabling one or more instances of the AFTR
   function on a device; each instance element is responsible for serving a
   group combination of B4s.  The data model assumes that each AFTR instance can: be
   enable/disabled, be provisioned with dedicated configuration data, an IPv4-in-IPv6
      encapsualtion/decapsulation function and maintain its own mapping table. a NAT function.

   o  The data model assumes that
   pools of IPv4 addresses can be provisioned to B4 element is an IPv4-in-IPv6 encapsulation function.

   Therefore, the AFTR.  The AFTR YANG module augments is designed to augment both the
   Interfaces YANG module [RFC7223] and the NAT YANG module in [I-D.sivakumar-yang-nat].

   As such, this

   [I-D.sivakumar-yang-nat] with DS-Lite specific features.  The B4 YANG
   module augments the interfaces YANG module.

   This document assumes [RFC4787][RFC5382][RFC5508] are enabled by
   default.  Also, the data model adheres to the recommendations in
   [RFC6888] and [RFC7857].  Further,  Furthermore, the data model supports state
   migration as per [RFC7785].

   PCP-related considerations are out of scope of the document.  A YANG
   data model for PCP is documented in [I-D.boucadair-pcp-yang].

module: ietf-dslite-aftr
  augment /nat:nat-module/nat:nat-instances/nat:nat-instance: /if:interfaces/if:interface:
    +--rw ipv6-address? aftr-ipv6-address?             inet:ipv6-address
    +--rw ipv4-address? aftr-ipv4-address?             inet:ipv4-address
    +--rw tunnel-mtu?                    uint16
    +--rw subscriber-mask? max-softwire-per-subscriber?   uint8
    +--rw state-migrate? v6-v4-dscp-preservation?       boolean
  augment /nat:nat-module/nat:nat-instances/nat:nat-instance:
    +--rw max-softwire-per-subscriber?   uint8 state-migrate?   boolean
    +--rw mss-clamping
    |
       +--rw mss-clamping-enable?   boolean
    |
       +--rw mss-value?             uint16
    +--rw v6-v4-dscp-preservation?       boolean
  augment /nat:nat-module/nat:nat-instances/nat:nat-instance/nat:mapping-table/nat:mapping-entry:
    +--rw b4-ip-address? b4-ipv6-address?    inet:ipv6-address
    +--rw v6-dscp?            uint8
    +--rw internal-v4-dscp?   uint8
    +--rw external-v4-dscp?   uint8

                Figure 1: 2: YANG Data Model for DS-Lite AFTR

   A B4 instance is provided with the IPv6 address of the AFTR to use,
   an (optional) instruction whether DSCP marking is to preserved when
   encapsulating an IPv4 packet in an IPv6 packet, and other optional
   parameters shown in Figure 3.

   module: ietf-dslite-b4
     augment /if:interfaces/if:interface:
       +--rw dslite-b4
          +--rw enable?                boolean
          +--rw dslite-b4-instances
             +--rw dslite-b4-instance* [id]
                +--rw id                         uint32
                +--rw name?                      string b4-ipv6-address?           inet:ipv6-address
       +--rw aftr-ipv6-addr aftr-ipv6-addr?            inet:ipv6-address
       +--rw ipv4-address? b4-ipv4-address?           inet:ipv4-address
       +--rw tunnel-mtu?                uint16
       +--rw v6-v4-dscp-preservation v6-v4-dscp-preservation?   boolean

                 Figure 2: 3: YANG Data Model for DS-Lite B4

3.  DS-Lite AFTR YANG Module

<CODE BEGINS> file "ietf-dslite-aftr@2017-07-27.yang" "ietf-dslite-aftr@2017-08-10.yang"

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

    import ietf-inet-types { prefix inet; }
    import ietf-nat ietf-interfaces { prefix if; }
    import iana-if-type { prefix nat; ianaift; }
    import ietf-nat {prefix nat;}

    organization "Softwire Working Group";
    contact
     "Mohamed Boucadair <mohamed.boucadair@orange.com>
      Christian Jacquenet <christian.jacquenet@orange.com>
      Senthil Sivakumar <ssenthil@cisco.com>";

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

      Copyright (c) 2017 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; see
      the RFC itself for full legal notices.";

    revision 2017-08-10 {
      description "The module augments also the Interface module.";
       reference "-ietf-04";
    }

    revision 2017-07-27 {
      description "Redesign the module as an augment of the NAT YANG module.";
       reference "-ietf-04";
    }

    revision 2017-07-03 {
      description "Fix some minor points.";
       reference "-ietf-03";
    }

    revision 2017-01-03 {
      description "Fixed a compilation error:
        https://github.com/mbj4668/pyang/issues/296.";
       reference "-ietf-02";
    }

    revision 2016-11-14 {
      description "Integrates the comments from Ian:
      add B4 module, add an MSS leaf, add more details about
      logging protocols, and other edits.";
       reference "-ietf-01";
    }

    revision 2016-07-27 {
      description "-00 IETF version.";
       reference "-ietf-00";
    }

    revision 2016-06-13 {
      description "Update the module.";
       reference "-04";
    }

    revision 2015-12-16 {
      description "Fix an error.";
       reference "-03";
    }

    revision 2015-09-01 {
      description "Add port threshold notifications.";
       reference "-02";
    }

    revision 2015-08-31 {
      description "Fix a timeout issue.";
       reference "-01";
    }

    revision 2015-08-17 {
      description "First spec.";
       reference "-00";
    }

// Augment NAT Interface module with AFTR parameters DS-Lite Softwire
augment "/nat:nat-module/nat:nat-instances/nat:nat-instance" "/if:interfaces/if:interface" {
   when "if:type = 'ianaift:tunnel'";

   description
        "Augments NAT Interface module with AFTR parameters."; parameters.
         IANA interface types are maintained at this registry:
         https://www.iana.org/assignments/ianaiftype-mib/ianaiftype-mib.

         tunnel (131),       -- Encapsulation interface";

   leaf ipv6-address aftr-ipv6-address {
           type inet:ipv6-address;
           description
             "IPv6 address of the dslite-aftr."; DS-Lite AFTR.";

           reference
              "RFC 6333.";
        }

    leaf ipv4-address aftr-ipv4-address {
        type inet:ipv4-address;
        default "192.0.0.1";

        description
          "IPv4 address of the DS-Lite AFTR.
          192.0.0.1 is reserved for the AFTR element.
          This address can be used to report ICMP
          problems and will appear in traceroute
          outputs.";

        reference
          "RFC 6333.";
    }

    leaf tunnel-mtu {
        type uint16;

        description
            "Configures a tunnel MTU.
            [RFC6908] specifies that since
            fragmentation and reassembly is not
            optimal, the operator should do
            everything possible to eliminate
            the need for it.  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
            accounts for the additional overhead
            (40 bytes).";

        reference
          "RFC 6908.";
    }

    leaf subscriber-mask {
        type uint8 {
            range "0 .. 128";
            }
        default "56";
        description
            "The subscriber-mask is an integer that indicates
             the length of significant bits to be applied on
             the source IPv6 address (internal side) to
             unambiguously identify a CPE.

             Subscriber-mask is a system-wide configuration
             parameter that is used to enforce generic
             per-subscriber policies (e.g., port-quota).

             The enforcement of these generic policies does not
             require the configuration of every subscriber's prefix.

             Example: suppose the 2001:db8:100:100::/56 prefix is
             assigned to a DS-Lite enabled CPE. Suppose also that the
             2001:db8:100:100::1 is the IPv6 address used by the
             B4 that resides in that CPE. When the AFTR
             receives a packet from this client,
             it applies the subscriber-mask (e.g., 56) on
             the source IPv6 address to compute the associated prefix
             for this client (that is 2001:db8:100:100::/56).  Then,
             the AFTR enforces policies based on that prefix
             (2001:db8:100:100::/56), not on the exact
             source IPv6 address";

        reference
          "RFC 7785.";
    }

    leaf state-migrate {
        type boolean;
        default true;
        description
            "State migration is enabled by default.";

        reference
          "RFC 7785.";
    }

    leaf max-softwire-per-subscriber max-softwire-per-subscriber {
        type uint8;
        default 1;

        description
         "Configures the maximum softwire per subscriber
         feature.

         A subscriber is uniquely identified by means
         of subscriber-mask.

         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 were enforced on a per-softwire basis,
         consume extra processing due to a large number
         of active softwires).";

        reference
          "Section 4 of RFC 7785.";
    }

    container mss-clamping {
        description
          "MSS rewriting configuration.";

        leaf mss-clamping-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.";
        }
     }

    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 [RFC6908],
         operators should use this model
         by provisioning the network such that
         the AFTR copies the DSCP value in the IPv4
         header to the Traffic Class field in
         the IPv6 header, after the encapsulation
         for the downstream traffic.";

        reference
          "Section 2.10 of RFC 6908.";
    }
}
// Augment NAT module with AFTR parameters

augment "/nat:nat-module/nat:nat-instances/nat:nat-instance" {

   description
        "Augments NAT module with AFTR parameters.";

    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 CPE.

          The AFTR uses the subscriber-mask to determine whether two
          IPv6 addresses belong to the same CPE (e.g., if the
          subscriber-mask 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.";
    }

    container mss-clamping {
        description
          "MSS rewriting configuration to avoid IPv6
          fragmentation.";

        leaf mss-clamping-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 mapping entry:  Extended NAT44 mapping Entry

augment "/nat:nat-module/nat:nat-instances/nat:nat-instance/nat:mapping-table/nat:mapping-entry"{
   description
     "Augments the NAT mapping table tables with DS-Lite specifics.";

    leaf b4-ip-address b4-ipv6-address {
        type inet:ipv6-address;

        description
            "Corresponds to the IPv6 address
            used by the B4 element.";

        reference
          "RFC 6333.";
     }

   leaf v6-dscp {
        type uint8;

        description
          "DSCP value used at the softwire level
          (i.e., IPv6 header).";
   }

   leaf internal-v4-dscp {
        type uint8;

        description
          "DSCP value of the encapsulated IPv4 packet.";
   }

   leaf external-v4-dscp {
        type uint8;

        description
          "DSCP value of the translated IPv4 packet
           as marked by the AFTR.";
   }
 }
}
<CODE ENDS>

4.  DS-Lite B4 YANG Module

<CODE BEGINS> file "ietf-dslite-b4@2017-07-27.yang" "ietf-dslite-b4@2017-08-10.yang"

module ietf-dslite-b4 {
    namespace "urn:ietf:params:xml:ns:yang:ietf-dslite-b4";
    prefix dslite-b4;

    import ietf-inet-types { prefix inet; }
    import ietf-interfaces { prefix if; }
    import iana-if-type { prefix ianaift; }

    organization "Softwire Working Group";
    contact
     "Mohamed Boucadair <mohamed.boucadair@orange.com>
      Christian Jacquenet <christian.jacquenet@orange.com>
      Senthil Sivakumar <ssenthil@cisco.com>";

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

      Copyright (c) 2017 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; see
      the RFC itself for full legal notices.";

    revision 2017-08-10 {
      description "Augment the interfaces YANG module.";
       reference "-ietf-05";
    }

    revision 2017-07-27 {
      description "Separate B4 from AFTR.";
       reference "-ietf-04";
    }

   container dslite-b4 {

       description
        "dslite-b4";

       leaf enable {
           type boolean;
           description
            "Enable/disable dslite-b4 function.";
       }

       container dslite-b4-instances {
          description
            "dslite-b4 instances";

           list dslite-b4-instance {
               key "id";
                 description
                   "a dslite-b4 instance.";

              leaf id

// Augment Interface module with DS-Lite Softwire
augment "/if:interfaces/if:interface" {
                 type uint32;
   when "if:type = 'ianaift:tunnel'";

   description
                   "dslite-b4 instance identifier.";
              }
        "Augments Interface module with B4 parameters.
         IANA interface types are maintained at this registry:
         https://www.iana.org/assignments/ianaiftype-mib/ianaiftype-mib.

         tunnel (131),       -- Encapsulation interface";

    leaf name b4-ipv6-address {
        type string; inet:ipv6-address;

        description
                   "A name associated with
          "The IPv6 address used by the dslite-b4 instance."; B4 element.";

        reference
             "RFC 6333.";
    }

    leaf aftr-ipv6-addr {
        type inet:ipv6-address;
                 mandatory true;

        description
           "The AFTR's IPv6 address.";

        reference
          "RFC 6333.";
    }

    leaf ipv4-address b4-ipv4-address {
        type inet:ipv4-address;
        default "192.0.0.2";

        description
          "IPv4 address of the DS-Lite B4.
          192.0.0.0/29 is reserved for the B4 element
          [RFC6333].
          This address can be used to report ICMP
          problems and will appear in traceroute
          outputs.";

        reference
             "RFC 6333.";
    }

    leaf tunnel-mtu {
        type uint16;
        description
            "Configures a tunnel MTU.
            [RFC6908] specifies that since
            fragmentation and reassembly is not
            optimal, the operator should do
            everything possible to eliminate
            the need for it.  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
            accounts for the additional overhead
            (40 bytes).";

         reference
             "RFC 6908.";
    }

    leaf v6-v4-dscp-preservation {
        type boolean;
           mandatory true;

        description
         "Copies the DSCP value from the IPv6 header
         and vice versa.
         According to Section 2.10 of [RFC6908],
         operators should use this model
         by provisioning the network such that
         the AFTR copies the DSCP value in the IPv4
         header to the Traffic Class field in
         the IPv6 header, after the encapsulation
         for the downstream traffic.";
       }
     }
   }
  }
}
<CODE ENDS>

5.  Security Considerations

   The YANG module defined in this memo is designed to be accessed via
   the NETCONF protocol [RFC6241].  The lowest NETCONF layer is the
   secure transport layer and the support of SSH is mandatory to
   implement secure transport [RFC6242].  The NETCONF access control
   model [RFC6536] provides means to restrict access for particular
   NETCONF users to a pre-configured subset of all available NETCONF
   protocol operations and contents.

   All data nodes defined in the YANG module which can be created,
   modified and deleted (i.e., config true, which is the default).
   These data nodes are considered sensitive.  Write operations (e.g.,
   edit-config) applied to these data nodes without proper protection
   can negatively affect network operations.

6.  IANA Considerations

   This document requests IANA to register the following URIs in the
   "IETF XML Registry" [RFC3688]:

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

            URI: urn:ietf:params:xml:ns:yang:ietf-dslite-b4
            Registrant Contact: The IESG.
            XML: N/A; the requested URI is an XML namespace.

   This document requests IANA to register the following YANG modules in
   the "YANG Module Names" registry [RFC6020].

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

            name: ietf-dslite-b4
            namespace: urn:ietf:params:xml:ns:yang:ietf-dslite-b4
            prefix: dslite-b4
            reference: RFC XXXX

7.  Acknowledgements

   Thanks to Q.  Wu for identifying a compiling error.

   Many thanks to Ian Farrer for the review and comments.

8.  References

8.1.  Normative references

   [I-D.sivakumar-yang-nat]
              Sivakumar, S., Boucadair, M., and S. Vinapamula, "YANG
              Data Model for Network Address Translation (NAT)", draft-
              sivakumar-yang-nat-07 (work in progress), July 2017.

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

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <http://www.rfc-editor.org/info/rfc6020>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <http://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,
              <http://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,
              <http://www.rfc-editor.org/info/rfc6333>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <http://www.rfc-editor.org/info/rfc6536>.

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

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
              <http://www.rfc-editor.org/info/rfc7223>.

8.2.  Informative references

   [I-D.boucadair-pcp-yang]
              Boucadair, M., Jacquenet, C., Sivakumar, S., and S.
              Vinapamula, "YANG Data Models for the Port Control
              Protocol (PCP)", draft-boucadair-pcp-yang-04 (work in
              progress), May 2017.

   [RFC4787]  Audet, F., Ed. and C. Jennings, "Network Address
              Translation (NAT) Behavioral Requirements for Unicast
              UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
              2007, <http://www.rfc-editor.org/info/rfc4787>.

   [RFC5382]  Guha, S., Ed., Biswas, K., Ford, B., Sivakumar, S., and P.
              Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
              RFC 5382, DOI 10.17487/RFC5382, October 2008,
              <http://www.rfc-editor.org/info/rfc5382>.

   [RFC5508]  Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
              Behavioral Requirements for ICMP", BCP 148, RFC 5508,
              DOI 10.17487/RFC5508, April 2009,
              <http://www.rfc-editor.org/info/rfc5508>.

   [RFC6087]  Bierman, A., "Guidelines for Authors and Reviewers of YANG
              Data Model Documents", RFC 6087, DOI 10.17487/RFC6087,
              January 2011, <http://www.rfc-editor.org/info/rfc6087>.

   [RFC6888]  Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
              A., and H. Ashida, "Common Requirements for Carrier-Grade
              NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
              April 2013, <http://www.rfc-editor.org/info/rfc6888>.

   [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,
              <http://www.rfc-editor.org/info/rfc6908>.

   [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,
              <http://www.rfc-editor.org/info/rfc7785>.

   [RFC7857]  Penno, R., Perreault, S., Boucadair, M., Ed., Sivakumar,
              S., and K. Naito, "Updates to Network Address Translation
              (NAT) Behavioral Requirements", BCP 127, RFC 7857,
              DOI 10.17487/RFC7857, April 2016,
              <http://www.rfc-editor.org/info/rfc7857>.

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
   USA

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