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+Internet Engineering Task Force (IETF)                    I. Farrer, Ed.
+Request for Comments: 8676                           Deutsche Telekom AG
+Category: Standards Track                              M. Boucadair, Ed.
+ISSN: 2070-1721                                                   Orange
+                                                           November 2019
+
+
+    YANG Modules for IPv4-in-IPv6 Address plus Port (A+P) Softwires
+
+Abstract
+
+   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.
+
+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/rfc8676.
+
+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.
+
+Table of Contents
+
+   1.  Introduction
+   2.  Terminology
+   3.  Overview of the Modules
+     3.1.  Overall Structure
+     3.2.  Configuration for Additional Components
+   4.  Softwire CE YANG Tree Diagram
+     4.1.  CE Tree Diagram
+     4.2.  Softwire CE Tree Diagram Description
+   5.  Softwire BR YANG Tree Diagram
+     5.1.  BR Tree Diagram
+     5.2.  Softwire BR Tree Diagram Description
+   6.  Softwire CE YANG Module
+   7.  BR Softwire YANG Module
+   8.  Common Softwire Element Groups YANG Module
+   9.  Security Considerations
+   10. IANA Considerations
+   11. References
+     11.1.  Normative References
+     11.2.  Informative References
+   Appendix A.  Configuration Examples
+     A.1.  Configuration Example for a lw4o6 BR Binding-Table
+     A.2.  Configuration Example for a MAP-E BR
+     A.3.  lw4o6 CE Configuration Example
+   Acknowledgements
+   Contributors
+   Authors' Addresses
+
+1.  Introduction
+
+   The IETF Softwire 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 plus
+   Port (A+P) softwire functional elements: Border Routers (BRs) and
+   Customer Edge (CE) (called "Customer Premises Equipment (CPE)" in
+   [RFC7596]).  The softwire mechanisms covered in this document are
+   Lightweight 4over6 (lw4o6) [RFC7596], Mapping of Address and Port
+   with Encapsulation (MAP-E) [RFC7597], and Mapping of Address and Port
+   using Translation (MAP-T) [RFC7599].
+
+   This document focuses on A+P mechanisms [RFC6346]; the reader can
+   refer to [RFC8513] for a YANG module for Dual-Stack Lite (DS-Lite)
+   [RFC6333].
+
+   This document defines YANG modules [RFC7950] that can be used to
+   configure and manage A+P softwire elements using the NETCONF
+   [RFC6241] or RESTCONF [RFC8040] protocols for:
+
+   *  Configuration
+
+   *  Operational State
+
+   *  Notifications
+
+2.  Terminology
+
+   The reader should be familiar with the concepts and terms defined in
+   [RFC7596], [RFC7597], [RFC7599], and the YANG data modeling language
+   defined in [RFC7950].
+
+   The YANG modules in this document adopt the Network Management
+   Datastore Architecture (NMDA) [RFC8342].  The meanings of the symbols
+   used in tree diagrams are defined in [RFC8340].
+
+   The document uses the abbreviation 'BR' as a general term for
+   softwire tunnel concentrators, including both MAP Border Routers
+   [RFC7597] and Lightweight 4over6 lwAFTRs [RFC7596].
+
+   For brevity, "algorithm" is used to refer to the "mapping algorithm"
+   defined in [RFC7597].
+
+   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.
+
+3.  Overview of the Modules
+
+3.1.  Overall Structure
+
+   The document defines the following two YANG modules for the
+   configuration and monitoring of softwire functional elements:
+
+      ietf-softwire-ce
+         Provides configuration and monitoring for softwire CE element.
+         This module is defined as augments to the interface YANG module
+         [RFC8343].
+
+      ietf-softwire-br
+         Provides configuration and monitoring for softwire BR element.
+
+   In addition, the following module is defined:
+
+      ietf-softwire-common
+         Contains groups of common functions that are imported into the
+         CE and BR modules.
+
+   This approach has been taken so that the various modules can be
+   easily extended to support additional softwire mechanisms, if
+   required.
+
+   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.
+
+   In the 'algo-instances' container, a choice statement 'data-plane' is
+   included to specify MAP-E (encapsulation) or MAP-T (translation).
+   Table 1 shows how these choices are used to indicate the desired
+   softwire mechanism:
+
+            +--------------------+-----------+---------------+
+            |   S46 Mechanism    |  ce-type? |  data-plane?  |
+            +====================+===========+===============+
+            | Lightweight 4over6 |  binding  |      n/a      |
+            +--------------------+-----------+---------------+
+            |       MAP-E        | algorithm | encapsulation |
+            +--------------------+-----------+---------------+
+            |       MAP-T        | algorithm |  translation  |
+            +--------------------+-----------+---------------+
+
+                    Table 1: Softwire Mechanism Choice
+                          Statement Enumeration
+
+   NETCONF notifications are also included.
+
+      |  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.
+
+3.2.  Configuration for Additional Components
+
+   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:
+
+   *  IPv6 forwarding and routing configuration, to enable the CE to
+      obtain one or more IPv6 prefixes for softwire usage.  A YANG
+      module for routing management is described in [RFC8349].
+
+   *  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 [RFC8349].
+
+   *  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 [RFC8512].
+
+   *  Stateless NAT46 management, which is required by 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 [RFC8512].
+
+   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.  Appendix A.3 provides XML examples of how
+   these modules can be used together.
+
+   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 configuration is necessary, the YANG modules
+   defined in [RFC8344] and [RFC8349] may be used.
+
+4.  Softwire CE YANG Tree Diagram
+
+4.1.  CE Tree Diagram
+
+   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).
+
+   This module augments "ietf-interfaces", defined in [RFC8343] 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 (Section 10) is set to 'aplusp'.
+
+   Figure 1 shows the tree structure of the softwire CE YANG module:
+
+
+   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
+
+                  Figure 1: Softwire CE YANG Tree Diagram
+
+4.2.  Softwire CE Tree Diagram Description
+
+   Additional information related to the operation of a CE element is
+   provided below:
+
+      softwire-payload-mtu:
+         optionally used to set the IPv4 Maximum Transmission Unit (MTU)
+         for the softwire.  Needed if the softwire implementation is
+         unable to correctly calculate the correct IPv4 MTU size
+         automatically.
+
+      softwire-path-mru:
+         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 [RFC4213]).
+
+      ce-type:
+         provides a choice statement allowing the binding or algorithmic
+         softwire mechanisms to be selected.
+
+   Further details relevant to binding softwire elements are as follows:
+
+      binding-ipv6info:
+         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'.
+
+      br-ipv6-addr:
+         sets the IPv6 address of the remote BR.
+
+   Additional details relevant to some of the important algorithmic
+   elements are provided below:
+
+      algo-versioning:
+         optionally used to associate a version number and/or timestamp
+         to the algorithm.  This can be used for logging/data retention
+         purposes [RFC7422].  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.
+
+      forwarding:
+         specifies whether the rule can be used as a 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 [RFC7598].
+
+      ea-len:
+         used to set the length of the Embedded-Address (EA), which is
+         defined in the mapping rule for a MAP domain.
+
+      data-plane:
+         provides a choice statement for either encapsulation (MAP-E) or
+         translation (MAP-T).
+
+      br-ipv6-addr:
+         defines the IPv6 address of the BR.  This information is valid
+         for MAP-E.
+
+      dmr-ipv6-prefix:
+         defines the Default Mapping Rule (DMR) IPv6 prefix of the BR.
+         This information is valid for MAP-T.
+
+   Additional information on the notification node is listed below:
+
+      ce-binding-ipv6-addr-change:
+         if the CE's binding IPv6 address changes for any reason, the
+         NETCONF client will be notified.
+
+5.  Softwire BR YANG Tree Diagram
+
+5.1.  BR Tree Diagram
+
+   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).
+
+   Figure 2 provides the tree structure of this module:
+
+   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
+
+                      Figure 2: Softwire BR YANG Tree
+
+5.2.  Softwire BR Tree Diagram Description
+
+   The descriptions for leaves that are common with the CE module are
+   provided in Section 4.2.  Descriptions for additional elements are
+   provided below:
+
+      binding-table-versioning:
+         optionally used to associate a version number and/or timestamp
+         to the binding table.  This can be used for logging or data
+         retention purposes [RFC7422].  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.
+
+      binding-entry:
+         used to define the binding relationship between 3-tuples
+         {lwB4's IPv6 address/prefix, the allocated IPv4 address,
+         restricted port-set}.  For detailed information, please refer
+         to [RFC7596].
+
+      softwire-num-max:
+         used to set the maximum number of softwire binding rules that
+         can be created on the lw4o6 element simultaneously.  This
+         parameter must not be set to zero because this is equivalent to
+         disabling the BR instance.
+
+      active-softwire-num:
+         holds the number of softwires currently provisioned on the BR
+         element.
+
+   Additional information on some of the important notification nodes is
+   listed below:
+
+      invalid-entry, added-entry, modified-entry:
+         used to notify the NETCONF client that a specific binding entry
+         or MAP rule has expired, been invalidated, added, or modified.
+
+6.  Softwire CE YANG Module
+
+   This module imports the modules defined in [RFC6991], [RFC8343], and
+   [RFC7224].  It also imports the 'ietf-softwire-common' and 'iana-
+   tunnel-type' modules [RFC8675].
+
+   <CODE BEGINS> file "ietf-softwire-ce@2019-11-16.yang"
+   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
+         "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 8676: YANG Modules for IPv4-in-IPv6 Address plus Port
+          Softwires";
+     }
+     import iana-tunnel-type {
+       prefix iana-tunnel-type;
+       reference
+         "RFC 8675: A YANG Data Model for Tunnel Interface 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 8676; see
+        the RFC itself for full legal notices.";
+
+     revision 2019-11-16 {
+       description
+         "Initial revision.";
+       reference
+         "RFC 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 softwire mechanisms are IPv4-over-IPv6 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 softwire instances.";
+       reference
+         "RFC 7596: Lightweight 4over6: An Extension to the Dual-Stack
+          Lite Architecture
+          RFC 7597: Mapping of Address and Port with Encapsulation
+          (MAP-E)
+          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
+         "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 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
+         "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, 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 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
+           "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>
+
+7.  BR Softwire YANG Module
+
+   This module imports typedefs from [RFC6991].  It also imports the
+   'ietf-softwire-common' module.
+
+   <CODE BEGINS> file "ietf-softwire-br@2019-11-16.yang"
+   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
+         "RFC 6991: Common YANG Data Types, Section 4";
+     }
+     import ietf-yang-types {
+       prefix yang;
+       reference
+         "RFC 6991: Common YANG Data Types, Section 3";
+     }
+     import ietf-softwire-common {
+       prefix softwire-common;
+       reference
+         "RFC 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 8676; see
+        the RFC itself for full legal notices.";
+
+     revision 2019-11-16 {
+       description
+         "Initial revision.";
+       reference
+         "RFC 8676: YANG Modules for IPv4-in-IPv6 Address plus Port
+          (A+P) Softwires";
+     }
+
+     /*
+      * Groupings
+      */
+
+     grouping port-set {
+       description
+         "Describes a set of 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 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 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
+           "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 softwire mechanisms are IPv4-over-IPv6 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 softwire instances.";
+       reference
+         "RFC 7596: Lightweight 4over6: An Extension to the Dual-Stack
+          Lite Architecture
+          RFC 7597: Mapping of Address and Port with Encapsulation
+          (MAP-E)
+          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
+         "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 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
+         "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, 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
+                     "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";
+                 reference
+                   "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";
+                 reference
+                   "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 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
+                       "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
+                        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
+                       "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
+                       "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
+                        for sending ICMPv6 errors messages";
+                     reference
+                       "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 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 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 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 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 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 set of parameters used for 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 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 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 instance event.";
+       }
+       leaf-list invalid-entry {
+         type leafref {
+           path "/br-instances/algorithm/algo-instance/name";
+         }
+         description
+           "Invalid 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>
+
+8.  Common Softwire Element Groups YANG Module
+
+   This module imports typedefs from [RFC6991].
+
+   The following YANG module contains definitions that are used by both
+   the softwire CE and softwire BR YANG modules.
+
+   <CODE BEGINS> file "ietf-softwire-common@2019-11-16.yang"
+   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
+         "RFC 6991: Common YANG Data Types, Section 4";
+     }
+     import ietf-yang-types {
+       prefix yang;
+       reference
+         "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 8676; see
+        the RFC itself for full legal notices.";
+
+     revision 2019-11-16 {
+       description
+         "Initial revision.";
+       reference
+         "RFC 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
+         "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 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
+         "RFC 7599: Mapping of Address and Port using Translation
+          (MAP-T)";
+     }
+
+     /*
+      * Groupings
+      */
+
+     grouping algorithm-instance {
+       description
+         "A collection of parameters that is used 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.";
+           reference
+             "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; if set, this rule is used as 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 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.
+
+            Discontinuities in the value of this counter can occur
+            at re-initialization of the management 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 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.
+
+            Discontinuities in the value of this counter can occur
+            at re-initialization of the management 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 and at
+            other times as indicated by the value of
+            'discontinuity-time'.";
+       }
+     }
+   }
+   <CODE ENDS>
+
+9.  Security Considerations
+
+   The YANG modules defined in this document are 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 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) to these
+   data nodes without proper protection can have a negative effect on
+   network operations.  An attacker who is able to access the BR can
+   undertake various attacks, such as:
+
+   *  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.
+
+   *  Setting the MTU to a low value, which may increase the number of
+      fragments ('softwire-payload-mtu').
+
+   *  Disabling hairpinning (i.e., setting 'enable-hairpinning' to
+      'false') to prevent communications between CEs.
+
+   *  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.
+
+   *  Setting 'icmpv4-rate' or 'icmpv6-rate' to a low value, which may
+      lead to the deactivation of ICMP messages handling.
+
+   *  Instructing the BR to install entries, which, in 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.
+
+   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:
+
+   *  the binding Table (/br-instances/binding/bind-instance/binding-
+      table)
+
+   *  the algorithm configuration (/br-instances/algorithm/algo-
+      instance/)
+
+   Security considerations related to lw4o6, MAP-T, and MAP-E are
+   discussed in [RFC7596], [RFC7597], and [RFC7599] respectively.
+
+   Security considerations given in [RFC7950] are also applicable here.
+
+10.  IANA Considerations
+
+   IANA has assigned the following new tunnel type under the tunnelType
+   subregistry of the "ifType Definitions" registry maintained in the
+   SMI Numbers registry [TUNNELTYPE-IANA-REGISTRY]:
+
+      Decimal:      18
+      Name:         aplusp
+      Description:  A+P encapsulation
+      Reference:    [RFC6346]
+
+   IANA has registered the following in the "ns" subregistry within the
+   "IETF XML Registry" [RFC3688]:
+
+      URI:  urn:ietf:params:xml:ns:yang:ietf-softwire-ce
+      Registrant Contact:  The IESG.
+      XML:  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; the requested URI is an XML namespace.
+
+      URI:  urn:ietf:params:xml:ns:yang:ietf-softwire-common
+      Registrant Contact:  The IESG.
+      XML:  N/A; the requested URI is an XML namespace.
+
+   IANA has registered the following YANG modules in the "YANG Module
+   Names" subregistry [RFC6020] within the "YANG Parameters" registry.
+
+      name:  ietf-softwire-ce
+      namespace:  urn:ietf:params:xml:ns:yang:ietf-softwire-ce
+      prefix:  softwire-ce
+      reference:  RFC 8676
+
+      name:  ietf-softwire-br
+      namespace:  urn:ietf:params:xml:ns:yang:ietf-softwire-br
+      prefix:  softwire-br
+      reference:  RFC 8676
+
+      name:  ietf-softwire-common
+      namespace:  urn:ietf:params:xml:ns:yang:ietf-softwire-common
+      prefix:  softwire-common
+      reference:  RFC 8676
+
+11.  References
+
+11.1.  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>.
+
+   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
+              the Network Configuration Protocol (NETCONF)", RFC 6020,
+              DOI 10.17487/RFC6020, October 2010,
+              <https://www.rfc-editor.org/info/rfc6020>.
+
+   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
+              and A. Bierman, Ed., "Network Configuration Protocol
+              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
+              <https://www.rfc-editor.org/info/rfc6241>.
+
+   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
+              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
+              <https://www.rfc-editor.org/info/rfc6242>.
+
+   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
+              RFC 6991, DOI 10.17487/RFC6991, July 2013,
+              <https://www.rfc-editor.org/info/rfc6991>.
+
+   [RFC7224]  Bjorklund, M., "IANA Interface Type YANG Module",
+              RFC 7224, DOI 10.17487/RFC7224, May 2014,
+              <https://www.rfc-editor.org/info/rfc7224>.
+
+   [RFC7596]  Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
+              Farrer, "Lightweight 4over6: An Extension to the Dual-
+              Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596,
+              July 2015, <https://www.rfc-editor.org/info/rfc7596>.
+
+   [RFC7597]  Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
+              Murakami, T., and T. Taylor, Ed., "Mapping of Address and
+              Port with Encapsulation (MAP-E)", RFC 7597,
+              DOI 10.17487/RFC7597, July 2015,
+              <https://www.rfc-editor.org/info/rfc7597>.
+
+   [RFC7598]  Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec,
+              W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for
+              Configuration of Softwire Address and Port-Mapped
+              Clients", RFC 7598, DOI 10.17487/RFC7598, July 2015,
+              <https://www.rfc-editor.org/info/rfc7598>.
+
+   [RFC7599]  Li, X., Bao, C., Dec, W., Ed., Troan, O., Matsushima, S.,
+              and T. Murakami, "Mapping of Address and Port using
+              Translation (MAP-T)", RFC 7599, DOI 10.17487/RFC7599, July
+              2015, <https://www.rfc-editor.org/info/rfc7599>.
+
+   [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>.
+
+   [RFC8675]  Boucadair, M., Farrer, I., and R. Asati, "A YANG Data
+              Model for Tunnel Interface Types", RFC 8675,
+              DOI 10.17487/RFC8675, November 2019,
+              <https://www.rfc-editor.org/info/rfc8675>.
+
+   [TUNNELTYPE-IANA-REGISTRY]
+              IANA, "Structure of Management Information (SMI) Numbers
+              (MIB Module Registrations)",
+              <https://www.iana.org/assignments/smi-numbers>.
+
+11.2.  Informative References
+
+   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
+              for IPv6 Hosts and Routers", RFC 4213,
+              DOI 10.17487/RFC4213, October 2005,
+              <https://www.rfc-editor.org/info/rfc4213>.
+
+   [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>.
+
+   [RFC6346]  Bush, R., Ed., "The Address plus Port (A+P) Approach to
+              the IPv4 Address Shortage", RFC 6346,
+              DOI 10.17487/RFC6346, August 2011,
+              <https://www.rfc-editor.org/info/rfc6346>.
+
+   [RFC7422]  Donley, C., Grundemann, C., Sarawat, V., Sundaresan, K.,
+              and O. Vautrin, "Deterministic Address Mapping to Reduce
+              Logging in Carrier-Grade NAT Deployments", RFC 7422,
+              DOI 10.17487/RFC7422, December 2014,
+              <https://www.rfc-editor.org/info/rfc7422>.
+
+   [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>.
+
+   [RFC8344]  Bjorklund, M., "A YANG Data Model for IP Management",
+              RFC 8344, DOI 10.17487/RFC8344, March 2018,
+              <https://www.rfc-editor.org/info/rfc8344>.
+
+   [RFC8349]  Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
+              Routing Management (NMDA Version)", RFC 8349,
+              DOI 10.17487/RFC8349, March 2018,
+              <https://www.rfc-editor.org/info/rfc8349>.
+
+   [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>.
+
+   [RFC8513]  Boucadair, M., Jacquenet, C., and S. Sivakumar, "A YANG
+              Data Model for Dual-Stack Lite (DS-Lite)", RFC 8513,
+              DOI 10.17487/RFC8513, January 2019,
+              <https://www.rfc-editor.org/info/rfc8513>.
+
+Appendix A.  Configuration Examples
+
+   The following sections provide examples of how the softwire YANG
+   modules can be used for configuring softwire elements.
+
+A.1.  Configuration Example for a lw4o6 BR Binding-Table
+
+   The lwAFTR maintains an address binding table that contains the
+   following 3-tuples:
+
+   *  IPv6 Address for a single lwB4
+
+   *  Public IPv4 Address
+
+   *  Restricted port-set
+
+   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 decapsulation.
+
+   Consider an example for the following lw4o6 binding table entry:
+
+   lwB4 Binding IPv6 Address:  2001:db8::1
+
+   lwB4 Binding IPv4 Address:  192.0.2.1
+
+   lwB4 PSID:                  0x34
+
+   lwB4 PSID Length            8
+
+   BR IPv6 Address:            2001:db8:1::2
+
+       <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>
+
+              Figure 3: lw4o6 Binding Table Configuration XML
+
+A.2.  Configuration Example for a MAP-E BR
+
+   A MAP-E BR is configured with forward mapping rules for the CEs it is
+   serving.  In this example (taken from [RFC7597], Appendix A, Example
+   2), the following parameters are required:
+
+   *  Rule IPv6 Prefix
+
+   *  Rule IPv4 Prefix
+
+   *  Rule EA-bit bit length
+
+   *  IPv6 Address of MAP-BR
+
+   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.
+
+   The transport type for the data plane also needs to be configured for
+   encapsulation to enable MAP-E and forwarding needs to be enabled.
+
+   Consider an example for the following MAP-E Forwarding Mapping Rule:
+
+   Data plane:         encapsulation
+
+   Rule IPv6 Prefix:   2001:db8::/40
+
+   Rule IPv4 Prefix:   192.0.2.0/24
+
+   Rule EA-bit Length:  16
+
+   BR IPv6 Address:    2001:db8:ffff::1
+
+   Figure 4 provides the example MAP-E BR configuration xml.
+
+       <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>
+
+                   Figure 4: MAP-E FMR Configuration XML
+
+A.3.  lw4o6 CE Configuration Example
+
+   This section provides XML examples for configuring a lw4o6 CE.
+   Examples for routing and NAT44 are also provided for convenience.
+
+   Consider an example for the following lw4o6 CE configuration:
+
+   lwB4 Binding IPv6 Address:  2001:db8::1
+
+   lwB4 Binding IPv4 Address:  192.0.2.1
+
+   lwB4 PSID:                  0x34
+
+   lwB4 PSID Length            8
+
+   BR IPv6 Address:            2001:db8:1::2
+
+   <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>
+
+                    Figure 5: lw4o6 CE Configuration XML
+
+   In the example depicted in Figure 5, the interface name is defined
+   for the softwire tunnel.  This name is then referenced by the routing
+   configuration for the IPv4 route.  Figure 6 provides an example
+   configuration for the CE's IPv4 routing using the YANG module
+   described in [RFC8349].
+
+   <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-unicas\
+             t-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>
+
+                Figure 6: lw4o6 CE Routing Configuration XML
+
+   Figure 7 provides an example configuration for the CE's NAPT44
+   function using the YANG module described in [RFC8512].
+
+   <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>
+
+                   Figure 7: lw4o6 NAT Configuration XML
+
+Acknowledgements
+
+   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.
+
+   Thanks to Sheng Jiang for the review.
+
+   Special thanks to Tom Petch and Martin Bjorklund for the detailed
+   review and suggestions.
+
+Contributors
+
+   The following individuals are co-authors:
+
+      Yong Cui
+      Tsinghua University
+      China
+      Phone: +86-10-6260-3059
+      Email: cuiyong@tsinghua.edu.cn
+
+      Qi Sun
+      Tsinghua University
+      China
+      Phone: +86-10-6278-5822
+      Email: sunqi.ietf@gmail.com
+
+      Linhui Sun
+      Tsinghua University
+      China
+      Phone: +86-10-6278-5822
+      Email: lh.sunlinh@gmail.com
+
+      Sladjana Zechlin
+      Deutsche Telekom AG
+      Germany
+      Email: sladjana.zechlin@telekom.de
+
+      Rajiv Asati
+      Cisco Systems, Inc.
+      United States of America
+      Email: Rajiva@cisco.com
+
+      Hao Wang
+      Tsinghua University
+      China
+      Phone: +86-10-6278-5822
+      Email: wangh13@mails.tsinghua.edu.cn
+
+Authors' Addresses
+
+   Ian Farrer (editor)
+   Deutsche Telekom AG
+   CTO-ATI, Landgrabenweg 151
+   53227 Bonn
+   Germany
+
+   Email: ian.farrer@telekom.de
+
+
+   Mohamed Boucadair (editor)
+   Orange
+   35000 Rennes
+   France
+
+   Email: mohamed.boucadair@orange.com