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Versions: (draft-sivakumar-yang-nat) 00 01 02 03 04 05 06

Network Working Group                                       M. Boucadair
Internet-Draft                                                    Orange
Intended status: Standards Track                            S. Sivakumar
Expires: April 14, 2018                                    Cisco Systems
                                                            C. Jacquenet
                                                                  Orange
                                                           S. Vinapamula
                                                        Juniper Networks
                                                                   Q. Wu
                                                                  Huawei
                                                        October 11, 2017


  A YANG Data Model for Network Address Translation (NAT) and Network
                        Prefix Translation (NPT)
                     draft-ietf-opsawg-nat-yang-06

Abstract

   For the sake of network automation and the need for programming
   Network Address Translation (NAT) function in particular, a data
   model for configuring and managing the NAT is essential.  This
   document defines a YANG module for the NAT function.

   NAT44, Network Address and Protocol Translation from IPv6 Clients to
   IPv4 Servers (NAT64), Customer-side transLATor (CLAT), Explicit
   Address Mappings for Stateless IP/ICMP Translation (SIIT EAM), and
   IPv6 Network Prefix Translation (NPTv6) are covered in this document.

Editorial Note (To be removed by RFC Editor)

   Please update this statement with the RFC number to be assigned to
   ths document:

   "This version of this YANG module is part of RFC XXXX;"

Status of This Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any



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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 14, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Overview of the NAT YANG Data Model . . . . . . . . . . . . .   5
     2.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Various NAT Flavors . . . . . . . . . . . . . . . . . . .   6
     2.3.  TCP, UDP and ICMP NAT Behavioral Requirements . . . . . .   6
     2.4.  Other Transport Protocols . . . . . . . . . . . . . . . .   6
     2.5.  IP Addresses Used for Translation . . . . . . . . . . . .   6
     2.6.  Port Set Assignment . . . . . . . . . . . . . . . . . . .   7
     2.7.  Port-Restricted IP Addresses  . . . . . . . . . . . . . .   7
     2.8.  NAT Mapping Entries . . . . . . . . . . . . . . . . . . .   7
     2.9.  Resource Limits . . . . . . . . . . . . . . . . . . . . .  10
     2.10. Binding the NAT Function to an External Interface or VRF   10
     2.11. Tree Structure  . . . . . . . . . . . . . . . . . . . . .  10
   3.  NAT YANG Module . . . . . . . . . . . . . . . . . . . . . . .  14
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  56
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  57
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  57
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  58
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  58
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  59
   Appendix A.  Sample Examples  . . . . . . . . . . . . . . . . . .  61
     A.1.  Traditional NAT44 . . . . . . . . . . . . . . . . . . . .  61
     A.2.  CGN . . . . . . . . . . . . . . . . . . . . . . . . . . .  63
     A.3.  CGN Pass-Through  . . . . . . . . . . . . . . . . . . . .  66



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     A.4.  NAT64 . . . . . . . . . . . . . . . . . . . . . . . . . .  67
     A.5.  Explicit Address Mappings for Stateless IP/ICMP
           Translation . . . . . . . . . . . . . . . . . . . . . . .  68
     A.6.  Static Mappings with Port Ranges  . . . . . . . . . . . .  71
     A.7.  Static Mappings with IP Prefixes  . . . . . . . . . . . .  71
     A.8.  Destination NAT . . . . . . . . . . . . . . . . . . . . .  72
     A.9.  CLAT  . . . . . . . . . . . . . . . . . . . . . . . . . .  75
     A.10. NPTv6 . . . . . . . . . . . . . . . . . . . . . . . . . .  75
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  78

1.  Introduction

   This document defines a data model for Network Address Translation
   (NAT) and Network Prefix Translation (NPT) capabilities using the
   YANG data modeling language [RFC7950].

   Traditional NAT is defined in [RFC2663], while Carrier Grade NAT
   (CGN) is defined in [RFC6888].  Unlike traditional NAT, the CGN is
   used to optimize the usage of global IP address space at the scale of
   a domain: a CGN is not managed by end users, but by service providers
   instead.  This document covers both traditional NATs and CGNs.

   This document also covers NAT64 [RFC6146], customer-side translator
   (CLAT) [RFC6877], Explicit Address Mappings for Stateless IP/ICMP
   Translation (EAM) [RFC7757], and IPv6 Network Prefix Translation
   (NPTv6) [RFC6296].  The full set of translation schemes that are in
   scope is included in Section 2.2.

   Sample examples are provided in Appendix A.  These examples are not
   intended to be exhaustive.

1.1.  Terminology

   This document makes use of the following terms:

   o  Basic NAT44: translation is limited to IP addresses alone
      (Section 2.1 of [RFC3022]).

   o  Network Address/Port Translator (NAPT): translation in NAPT is
      extended to include IP addresses and transport identifiers (such
      as a TCP/UDP port or ICMP query ID); refer to Section 2.2 of
      [RFC3022].

   o  Destination NAT: is a translation that acts on the destination IP
      address and/or destination port number.  This flavor is usually
      deployed in load balancers or at devices in front of public
      servers.




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   o  Port-restricted IPv4 address: An IPv4 address with a restricted
      port set.  Multiple hosts may share the same IPv4 address;
      however, their port sets must not overlap [RFC7596].

   o  Restricted port set: A non-overlapping range of allowed external
      ports to use for NAT operation.  Source ports of IPv4 packets
      translated by a NAT must belong to the assigned port set.  The
      port set is used for all port-aware IP protocols [RFC7596].

   o  Internal Host: A host that may solicit a NAT or an NPTv6 (or both)
      capability to send to and receive traffic from the Internet.

   o  Internal Address/prefix: The IP address/prefix of an internal
      host.

   o  External Address: The IP address/prefix assigned by a NAT/NPTv6 to
      an internal host; this is the address that will be seen by a
      remote host on the Internet.

   o  Mapping: denotes a state at the NAT that is necessary for network
      address and/or port translation.

   o  Dynamic implicit mapping: is created implicitly as a side effect
      of traffic such as an outgoing TCP SYN or an outgoing UDP packet.
      A validity lifetime is associated with this mapping.

   o  Dynamic explicit mapping: is created as a result of an explicit
      request, e.g., PCP message [RFC6887].  A validity lifetime is
      associated with this mapping.

   o  Static explicit mapping: is created manually.  This mapping is
      likely to be maintained by the NAT function till an explicit
      action is executed to remove it.

   The usage of the term NAT in this document refers to any NAT flavor
   (NAT44, NAT64, etc.) indifferently.

   This document uses the term "session" as defined in [RFC2663] and
   [RFC6146] for NAT64.

1.2.  Tree Diagrams

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

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

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



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

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

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

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

2.  Overview of the NAT YANG Data Model

2.1.  Overview

   The NAT YANG module is designed to cover dynamic implicit mappings
   and static explicit mappings.  The required functionality to instruct
   dynamic explicit mappings is defined in separate documents such as
   [I-D.boucadair-pcp-yang].  Considerations about instructing explicit
   dynamic means (e.g., [RFC6887], [RFC6736], or [RFC8045]) are out of
   scope.

   A single NAT device can have multiple NAT instances (nat-instance);
   each of these instances can be provided with its own policies (e.g.,
   be responsible for serving a group of hosts).  This document does not
   make any assumption about how internal hosts or flows are associated
   with a given NAT instance.

   The NAT YANG module assumes that each NAT instance can be enabled/
   disabled, be provisioned with a specific set of configuration data,
   and maintains its own mapping tables.

   Further, the NAT YANG module allows for a NAT instance to be provided
   with multiple NAT policies (nat-policy).  The document does not make
   any assumption about how flows are associated with a given NAT policy
   of a given NAT instance.  Classification filters are out of scope.

   Defining multiple NAT instances or configuring multiple NAT policies
   within one single NAT instance is implementation- and deployment-
   specific.

   To accommodate deployments where [RFC6302] is not enabled, this YANG
   module allows to instruct a NAT function to log the destination port
   number.  The reader may refer to [I-D.ietf-behave-ipfix-nat-logging]
   which provides the templates to log the destination ports.





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2.2.  Various NAT Flavors

   The following modes are supported:

   1.   Basic NAT44
   2.   NAPT
   3.   Destination NAT
   4.   Port-restricted NAT
   5.   Stateful and stateless NAT64
   6.   EAM SIIT
   7.   CLAT
   8.   NPTv6
   9.   Combination of Basic NAT/NAPT and Destination NAT
   10.  Combination of port-restricted and Destination NAT
   11.  Combination of NAT64 and EAM

   [I-D.ietf-softwire-dslite-yang] specifies an extension to support DS-
   Lite.

2.3.  TCP, UDP and ICMP NAT Behavioral Requirements

   This document assumes [RFC4787][RFC5382][RFC5508] are enabled by
   default.

   Furthermore, the NAT YANG module relies upon the recommendations
   detailed in [RFC6888] and [RFC7857].

2.4.  Other Transport Protocols

   The module is structured to support other protocols than UDP, TCP,
   and ICMP.  The mapping table is designed so that it can indicate any
   transport protocol.  For example, this module may be used to manage a
   DCCP-capable NAT that adheres to [RFC5597].

   Future extensions can be defined to cover NAT-related considerations
   that are specific to other transport protocols such as SCTP
   [I-D.ietf-tsvwg-natsupp].  Typically, the mapping entry can be
   extended to record two optional SCTP-specific parameters: Internal
   Verification Tag (Int-VTag) and External Verification Tag (Ext-VTag).

2.5.  IP Addresses Used for Translation

   The NAT YANG module assumes that blocks of IP external addresses
   (external-ip-address-pool) can be provisioned to the NAT function.
   These blocks may be contiguous or not.

   This behavior is aligned with [RFC6888] which specifies that a NAT
   function should not have any limitations on the size or the



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   contiguity of the external address pool.  In particular, the NAT
   function must be configurable with contiguous or non-contiguous
   external IPv4 address ranges.

   Likewise, one or multiple IP address pools may be configured for
   Destination NAT (dst-ip-address-pool).

2.6.  Port Set Assignment

   Port numbers can be assigned by a NAT individually (that is, a single
   port is a assigned on a per session basis).  Nevertheless, this port
   allocation scheme may not be optimal for logging purposes.
   Therefore, a NAT function should be able to assign port sets (e.g.,
   [RFC7753]) to optimize the volume of the logging data (REQ-14 of
   [RFC6888]).  Both features are supported in the NAT YANG module.

   When port set assignment is activated (i.e., port-allocation-
   type==port-range-allocation), the NAT can be provided with the size
   of the port set to be assigned (port-set-size).

2.7.  Port-Restricted IP Addresses

   Some NATs require to restrict the port numbers (e.g., Lightweight
   4over6 [RFC7596], MAP-E [RFC7597]).  Two schemes of port set
   assignments (port-set-restrict) are supported in this document:

   o  Simple port range: is defined by two port values, the start and
      the end of the port range [RFC8045].

   o  Algorithmic: an algorithm is defined in [RFC7597] to characterize
      the set of ports that can be used.

2.8.  NAT Mapping Entries

   A TCP/UDP mapping entry maintains an association between the
   following information:

      (internal-src-address, internal-src-port) (internal-dst-address,
      internal-dst-port) <=> (external-src-address, external-src-port)
      (external-dst-address, external-dst-port)

   An ICMP mapping entry maintains an association between the following
   information:

      (internal-src-address, internal-dst-address, internal ICMP/ICMPv6
      identifier) <=> (external-src-address, external-dst-address,
      external ICMP/ICMPv6 identifier)




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   To cover TCP, UDP, and ICMP, the NAT YANG module assumes the
   following structure of a mapping entry:

   type:   Indicates how the mapping was instantiated.  For example, it
      may indicate whether a mapping is dynamically instantiated by a
      packet or statically configured.

   transport-protocol:  Indicates the transport protocol (e.g., UDP,
      TCP, ICMP) of a given mapping.

   internal-src-address:  Indicates the source IP address as used by an
      internal host.

   internal-src-port:  Indicates the source port number (or ICMP
      identifier) as used by an internal host.

   external-src-address:   Indicates the source IP address as assigned
      by the NAT.

   external-src-port:   Indicates the source port number (or ICMP
      identifier) as assigned by the NAT.

   internal-dst-address:  Indicates the destination IP address as used
      by an internal host when sending a packet to a remote host.

   internal-dst-port:   Indicates the destination IP address as used by
      an internal host when sending a packet to a remote host.

   external-dst-address:  Indicates the destination IP address used by a
      NAT when processing a packet issued by an internal host towards a
      remote host.

   external-dst-port:   Indicates the destination port number used by a
      NAT when processing a packet issued by an internal host towards a
      remote host.

   In order to cover both NAT64 and NAT44 flavors in particular, the NAT
   mapping structure allows to include an IPv4 or an IPv6 address as an
   internal IP address.  Remaining fields are common to both NAT
   schemes.

   For example, the mapping that will be created by a NAT64 upon receipt
   of a TCP SYN from source address 2001:db8:aaaa::1 and source port
   number 25636 to destination IP address 2001:db8:1234::198.51.100.1
   and destination port number 8080 is characterized as follows:

   o  type: dynamic implicit mapping.
   o  transport-protocol: TCP (6)



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   o  internal-src-address: 2001:db8:aaaa::1
   o  internal-src-port: 25636
   o  external-src-address: T (an IPv4 address configured on the NAT64)
   o  external-src-port: t (a port number that is chosen by the NAT64)
   o  internal-dst-address: 2001:db8:1234::198.51.100.1
   o  internal-dst-port: 8080
   o  external-dst-address: 198.51.100.1
   o  external-dst-port: 8080

   The mapping that will be created by a NAT44 upon receipt of an ICMP
   request from source address 198.51.100.1 and ICMP identifier (ID1) to
   destination IP address 198.51.100.11 is characterized as follows:

   o  type: dynamic implicit mapping.
   o  transport-protocol: ICMP (1)
   o  internal-src-address: 198.51.100.1
   o  internal-src-port: ID1
   o  external-src-address: T (an IPv4 address configured on the NAT44)
   o  external-src-port: ID2 (an ICMP identifier that is chosen by the
      NAT44)
   o  internal-dst-address: 198.51.100.11

   The mapping that will be created by a NAT64 upon receipt of an ICMP
   request from source address 2001:db8:aaaa::1 and ICMP identifier
   (ID1) to destination IP address 2001:db8:1234::198.51.100.1 is
   characterized as follows:

   o  type: dynamic implicit mapping.
   o  transport-protocol: ICMPv6 (58)
   o  internal-src-address: 2001:db8:aaaa::1
   o  internal-src-port: ID1
   o  external-src-address: T (an IPv4 address configured on the NAT64)
   o  external-src-port: ID2 (an ICMP identifier that is chosen by the
      NAT64)
   o  internal-dst-address: 2001:db8:1234::198.51.100.1
   o  external-dst-address: 198.51.100.1

   Note that a mapping table is maintained only for stateful NAT
   functions.  Particularly:

   o  No mapping table is maintained for NPTv6 given that it is
      stateless and transport-agnostic.

   o  The double translations are stateless in CLAT if a dedicated IPv6
      prefix is provided for CLAT.  If not, a stateful NAT44 will be
      required.

   o  No per-flow mapping is maintained for EAM [RFC7757].



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   o  No mapping table is maintained for stateless NAT64.  As a
      reminder, in such deployments internal IPv6 nodes are addressed
      using IPv4-translatable IPv6 addresses, which enable them to be
      accessed by IPv4 nodes [RFC6052].

2.9.  Resource Limits

   In order to comply with CGN deployments in particular, the NAT YANG
   module allows limiting the number of external ports per subscriber
   (port-quota) and the amount of state memory allocated per mapping and
   per subscriber (mapping-limit and connection-limit).  According to
   [RFC6888], the model allows for the following:

   o  Per-subscriber limits are configurable by the NAT administrator.

   o  Per-subscriber limits are configurable independently per transport
      protocol.

   o  Administrator-adjustable thresholds to prevent a single subscriber
      from consuming excessive CPU resources from the NAT (e.g., rate-
      limit the subscriber's creation of new mappings) can be
      configured.

2.10.  Binding the NAT Function to an External Interface or VRF

   The model allows to specify the interface or Virtual Routing and
   Forwarding (VRF) instance on which the NAT function must be applied
   (external-realm).  Distinct interfaces/VRFs can be provided as a
   function of the NAT policy (see for example, Section 4 of [RFC7289]).

   If no external interface/VRF is provided, this assumes that the
   system is able to determine the external interface/VRF instance on
   which the NAT will be applied.  Typically, the WAN and LAN interfaces
   of a CPE is determined by the CPE.

2.11.  Tree Structure

   The tree structure of the NAT YANG module is provided below:

module: ietf-nat
    +--rw nat-module
       +--rw nat-instances
          +--rw nat-instance* [id]
             +--rw id                  uint32
             +--rw name?               string
             +--rw enable?             boolean
             +--rw nat-capabilities
             |  +--rw nat-flavor*                                   identityref



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             |  +--rw nat44-flavor*                                 identityref
             |  +--rw restricted-port-support?                      boolean
             |  +--rw static-mapping-support?                       boolean
             |  +--rw port-randomization-support?                   boolean
             |  +--rw port-range-allocation-support?                boolean
             |  +--rw port-preservation-suport?                     boolean
             |  +--rw port-parity-preservation-support?             boolean
             |  +--rw address-roundrobin-support?                   boolean
             |  +--rw paired-address-pooling-support?               boolean
             |  +--rw endpoint-independent-mapping-support?         boolean
             |  +--rw address-dependent-mapping-support?            boolean
             |  +--rw address-and-port-dependent-mapping-support?   boolean
             |  +--rw endpoint-independent-filtering-support?       boolean
             |  +--rw address-dependent-filtering?                  boolean
             |  +--rw address-and-port-dependent-filtering?         boolean
             +--rw nat-pass-through* [nat-pass-through-id]
             |  +--rw nat-pass-through-id      uint32
             |  +--rw nat-pass-through-pref?   inet:ip-prefix
             |  +--rw nat-pass-through-port?   inet:port-number
             +--rw nat-policy* [policy-id]
             |  +--rw policy-id                        uint32
             |  +--rw clat-parameters
             |  |  +--rw clat-ipv6-prefixes* [clat-ipv6-prefix]
             |  |  |  +--rw clat-ipv6-prefix    inet:ipv6-prefix
             |  |  +--rw clat-ipv4-prefixes* [clat-ipv4-prefix]
             |  |     +--rw clat-ipv4-prefix    inet:ipv4-prefix
             |  +--rw nptv6-prefixes* [translation-id]
             |  |  +--rw translation-id          uint32
             |  |  +--rw internal-ipv6-prefix?   inet:ipv6-prefix
             |  |  +--rw external-ipv6-prefix?   inet:ipv6-prefix
             |  +--rw eam* [eam-ipv4-prefix]
             |  |  +--rw eam-ipv4-prefix    inet:ipv4-prefix
             |  |  +--rw eam-ipv6-prefix?   inet:ipv6-prefix
             |  +--rw nat64-prefixes* [nat64-prefix]
             |  |  +--rw nat64-prefix               inet:ipv6-prefix
             |  |  +--rw destination-ipv4-prefix* [ipv4-prefix]
             |  |  |  +--rw ipv4-prefix    inet:ipv4-prefix
             |  |  +--rw stateless-enable?          boolean
             |  +--rw external-ip-address-pool* [pool-id]
             |  |  +--rw pool-id             uint32
             |  |  +--rw external-ip-pool?   inet:ipv4-prefix
             |  +--rw port-set-restrict
             |  |  +--rw (port-type)?
             |  |     +--:(port-range)
             |  |     |  +--rw start-port-number?   inet:port-number
             |  |     |  +--rw end-port-number?     inet:port-number
             |  |     +--:(port-set-algo)
             |  |        +--rw psid-offset?         uint8



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             |  |        +--rw psid-len             uint8
             |  |        +--rw psid                 uint16
             |  +--rw dst-nat-enable?                  boolean
             |  +--rw dst-ip-address-pool* [pool-id]
             |  |  +--rw pool-id            uint32
             |  |  +--rw dst-in-ip-pool?    inet:ip-prefix
             |  |  +--rw dst-out-ip-pool?   inet:ip-prefix
             |  +--rw supported-transport-protocols* [transport-protocol-id]
             |  |  +--rw transport-protocol-id      uint8
             |  |  +--rw transport-protocol-name?   string
             |  +--rw subscriber-mask-v6?              uint8
             |  +--rw subscriber-match* [sub-match-id]
             |  |  +--rw sub-match-id    uint32
             |  |  +--rw sub-mask        inet:ip-prefix
             |  +--rw paired-address-pooling?          boolean
             |  +--rw nat-mapping-type?                enumeration
             |  +--rw nat-filtering-type?              enumeration
             |  +--rw port-quota* [quota-type]
             |  |  +--rw port-limit?   uint16
             |  |  +--rw quota-type    enumeration
             |  +--rw port-allocation-type?            enumeration
             |  +--rw address-roundrobin-enable?       boolean
             |  +--rw port-set
             |  |  +--rw port-set-size?      uint16
             |  |  +--rw port-set-timeout?   uint32
             |  +--rw timers
             |  |  +--rw udp-timeout?               uint32
             |  |  +--rw tcp-idle-timeout?          uint32
             |  |  +--rw tcp-trans-open-timeout?    uint32
             |  |  +--rw tcp-trans-close-timeout?   uint32
             |  |  +--rw tcp-in-syn-timeout?        uint32
             |  |  +--rw fragment-min-timeout?      uint32
             |  |  +--rw icmp-timeout?              uint32
             |  |  +--rw per-port-timeout* [port-number]
             |  |  |  +--rw port-number     inet:port-number
             |  |  |  +--rw port-timeout    inet:port-number
             |  |  +--rw hold-down-timeout?         uint32
             |  |  +--rw hold-down-max?             uint32
             |  +--rw algs* [alg-name]
             |  |  +--rw alg-name                  string
             |  |  +--rw alg-transport-protocol?   uint32
             |  |  +--rw alg-transport-port?       inet:port-number
             |  |  +--rw alg-status?               boolean
             |  +--rw all-algs-enable?                 boolean
             |  +--rw notify-pool-usage
             |  |  +--rw pool-id?                     uint32
             |  |  +--rw notify-pool-hi-threshold     percent
             |  |  +--rw notify-pool-low-threshold?   percent



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             |  +--rw external-realm
             |     +--rw (realm-type)?
             |        +--:(interface)
             |        |  +--rw external-interface?      if:interface-ref
             |        +--:(vrf)
             |           +--rw external-vrf-instance?   identityref
             +--rw mapping-limit
             |  +--rw limit-per-subscriber?   uint32
             |  +--rw limit-per-vrf?          uint32
             |  +--rw limit-per-subnet?       inet:ip-prefix
             |  +--rw limit-per-instance      uint32
             |  +--rw limit-per-udp           uint32
             |  +--rw limit-per-tcp           uint32
             |  +--rw limit-per-icmp          uint32
             +--rw connection-limit
             |  +--rw limit-per-subscriber?   uint32
             |  +--rw limit-per-vrf?          uint32
             |  +--rw limit-per-subnet?       inet:ip-prefix
             |  +--rw limit-per-instance      uint32
             |  +--rw limit-per-udp           uint32
             |  +--rw limit-per-tcp           uint32
             |  +--rw limit-per-icmp          uint32
             +--rw logging-info
             |  +--rw logging-enable?        boolean
             |  +--rw destination-address    inet:ip-prefix
             |  +--rw destination-port       inet:port-number
             |  +--rw (protocol)?
             |     +--:(syslog)
             |     |  +--rw syslog?                boolean
             |     +--:(ipfix)
             |     |  +--rw ipfix?                 boolean
             |     +--:(ftp)
             |        +--rw ftp?                   boolean
             +--rw mapping-table
             |  +--rw mapping-entry* [index]
             |     +--rw index                   uint32
             |     +--rw type?                   enumeration
             |     +--rw transport-protocol?     uint8
             |     +--rw internal-src-address?   inet:ip-prefix
             |     +--rw internal-src-port
             |     |  +--rw start-port-number?   inet:port-number
             |     |  +--rw end-port-number?     inet:port-number
             |     +--rw external-src-address?   inet:ip-prefix
             |     +--rw external-src-port
             |     |  +--rw start-port-number?   inet:port-number
             |     |  +--rw end-port-number?     inet:port-number
             |     +--rw internal-dst-address?   inet:ip-prefix
             |     +--rw internal-dst-port



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             |     |  +--rw start-port-number?   inet:port-number
             |     |  +--rw end-port-number?     inet:port-number
             |     +--rw external-dst-address?   inet:ip-prefix
             |     +--rw external-dst-port
             |     |  +--rw start-port-number?   inet:port-number
             |     |  +--rw end-port-number?     inet:port-number
             |     +--rw lifetime?               uint32
             +--ro statistics
                +--ro traffic-statistics
                |  +--ro sent-packet?      yang:zero-based-counter64
                |  +--ro sent-byte?        yang:zero-based-counter64
                |  +--ro rcvd-packet?      yang:zero-based-counter64
                |  +--ro rcvd-byte?        yang:zero-based-counter64
                |  +--ro dropped-packet?   yang:zero-based-counter64
                |  +--ro dropped-byte?     yang:zero-based-counter64
                +--ro mapping-statistics
                |  +--ro total-mappings?        uint32
                |  +--ro total-tcp-mappings?    uint32
                |  +--ro total-udp-mappings?    uint32
                |  +--ro total-icmp-mappings?   uint32
                +--ro pool-stats
                   +--ro pool-id?             uint32
                   +--ro address-allocated?   uint32
                   +--ro address-free?        uint32
                   +--ro port-stats
                      +--ro ports-allocated?   uint32
                      +--ro ports-free?        uint32

  notifications:
    +---n nat-event
       +--ro id?                      -> /nat-module/nat-instances/nat-instance/id
       +--ro policy-id?               -> /nat-module/nat-instances/nat-instance/nat-policy/policy-id
       +--ro pool-id?                 -> /nat-module/nat-instances/nat-instance/nat-policy/external-ip-address-pool/pool-id
       +--ro notify-pool-threshold    percent


3.  NAT YANG Module

<CODE BEGINS> file "ietf-nat@2017-10-12.yang"

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

  //namespace to be assigned by IANA
  prefix "nat";

  import ietf-inet-types { prefix inet; }



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  import ietf-yang-types { prefix yang; }
  import ietf-interfaces { prefix if; }

  organization "IETF OPSAWG Working Group";

  contact
    "Mohamed Boucadair <mohamed.boucadair@orange.com>
     Senthil Sivakumar <ssenthil@cisco.com>
     Chritsian Jacquenet <christian.jacquenet@orange.com>
     Suresh Vinapamula <sureshk@juniper.net>
     Qin Wu <bill.wu@huawei.com>";

  description
    "This module is a YANG module for NAT implementations
     (including NAT44 and NAT64 flavors).

     Copyright (c) 2017 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

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

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

  revision 2017-10-12 {
    description "Comments from Mahesh Jethanandani.";
    reference "-ietf-05";
  }

  revision 2017-10-02 {
    description "Comments from Rajiv Asati to call out
                 explicitly stateless NAT64.";
    reference "-ietf-04";
  }

  revision 2017-09-27 {
    description "Comments from Kris Poscic about NAT44, mainly:
         - Allow for multiple NAT policies within the same instance.
         - Associate an external interface/vrf per NAT policy.";
    reference "-ietf-04";
  }

  revision 2017-09-18 {



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    description "Comments from Tore Anderson about EAM-SIIT.";
    reference "-ietf-03";
  }

  revision 2017-08-23 {
    description "Comments from F. Baker about NPTv6.";
    reference "-ietf-02";
  }

  revision 2017-08-21 {
    description " Includes CLAT (Lee/Jordi).";
    reference "-ietf-01";
  }

  revision 2017-08-03 {
    description "Integrates comments from OPSAWG CFA.";
    reference "-ietf-00";
  }

  revision 2017-07-03 {
    description "Integrates comments from D. Wing and T. Zhou.";
    reference "-07";
  }

  revision 2015-09-08 {
    description "Fixes few YANG errors.";

    reference "-02";
  }

  revision 2015-09-07 {
    description "Completes the NAT64 model.";
    reference "01";
  }

  revision 2015-08-29 {
    description "Initial version.";
    reference "00";
  }

  /*
   * Definitions
   */

  typedef percent {
    type uint8 {
      range "0 .. 100";
    }



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    description
      "Percentage";
  }

  /*
   * Identities
   */

  identity nat-type {
    description
      "Base identity for nat type.";
  }

  identity nat44 {
    base nat:nat-type;

    description
      "Identity for traditional NAT support.";

    reference
      "RFC 3022.";
  }

  identity basic-nat {
    base nat:nat44;

    description
      "Identity for Basic NAT support.";

    reference
      "RFC 3022.";
  }

  identity napt {
    base nat:nat44;

    description
      "Identity for NAPT support.";

    reference
      "RFC 3022.";
  }

  identity restricted-nat {
    base nat:nat44;

    description
      "Identity for Port-Restricted NAT support.";



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    reference
      "RFC 7596.";
  }

  identity dst-nat {
    base nat:nat-type;

    description
      "Identity for Destination NAT support.";
  }

  identity nat64 {
    base nat:nat-type;

    description
      "Identity for NAT64 support.";

    reference
      "RFC 6146.";
  }

  identity clat {
    base nat:nat-type;

    description
      "Identity for CLAT support.";

    reference
      "RFC 6877.";
  }

  identity eam {
    base nat:nat-type;

    description
      "Identity for EAM support.";

    reference
     "RFC 7757.";
  }

  identity nptv6 {
    base nat:nat-type;

    description
      "Identity for NPTv6 support.";

    reference



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      "RFC 6296.";
  }

  identity vrf-routing-instance {
    description
      "This identity represents a VRF routing instance.";

    reference
      "Section 8.9 of RFC 4026.";
  }

 /*
  * Grouping
  */

  // port numbers: single or port-range

  grouping port-number {
    description
      "Individual port or a range of ports.
       When only start-port-numbert is present,
       it represents a single port.";

    leaf start-port-number {
      type inet:port-number;

      description
        "Begining of the port range.";

      reference
        "Section 3.2.9 of RFC 8045.";
    }

    leaf end-port-number {
      type inet:port-number;

      must ". >= ../start-port-number"
        {
          error-message
            "The end-port-number must be greater than or
             equal to start-port-number.";
        }
      description
        "End of the port range.";

      reference
        "Section 3.2.10 of RFC 8045.";
    }



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  }

  // Set of ports

  grouping port-set {
    description
      "Indicates a set of ports.
       It may be a simple port range, or use the PSID algorithm
       to represent a range of transport layer
       ports which will be used by a NAPT.";

    choice port-type {
      default port-range;

      description
        "Port type: port-range or port-set-algo.";

      case port-range {
        /*leaf start-port-number {
          type inet:port-number;
          description
            "Begining of the port range.";

          reference
            "Section 3.2.9 of RFC 8045.";
         }

         leaf end-port-number {
           type inet:port-number;

           description
             "End of the port range.";

           reference
             "Section 3.2.10 of RFC 8045.";
         }*/
         uses port-number;
       }

      case port-set-algo {
        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



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             port range. In MAP-E/T, the default value is 6,
             which excludes system ports by default and assigns
             port ranges distributed across the entire port
             space.";
        }

        leaf psid-len {
          type uint8 {
             range 0..15;
          }
          mandatory true;

         description
           "The length of PSID, representing the sharing
            ratio for an IPv4 address.";
        }

        leaf psid {
          type uint16;
          mandatory true;

          description
            "Port Set Identifier (PSID) value, which
             identifies a set of ports algorithmically.";
        }
      }
    }
  }

  // Mapping Entry

  grouping mapping-entry {
    description
      "NAT mapping entry.";

    leaf index {
      type uint32;

      description
        "A unique identifier of a mapping entry.";
    }

    leaf type {
      type enumeration {
        enum "static"  {
          description
            "The mapping entry is manually
             configured.";



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        }

        enum "dynamic-explicit" {
          description
            "This mapping is created by an
             outgoing packet.";
        }

        enum "dynamic-implicit" {
          description
            "This mapping is created by an
             explicit  dynamic message.";
        }
      }
        description
          "Indicates the type of a mapping entry. E.g.,
           a mapping can be: static, implicit dynamic
           or explicit dynamic.";
    }

    leaf transport-protocol {
      type uint8;

      description
        "Upper-layer protocol associated with this mapping.
         Values are taken from the IANA protocol registry.
         For example, this field contains 6 (TCP) for a TCP
         mapping or 17 (UDP) for a UDP mapping. No transport
         protocol is indicated if a mapping applies for any
         protocol.";
    }

    leaf internal-src-address {
      type inet:ip-prefix;

      description
        "Corresponds to the source IPv4/IPv6 address/prefix
         of the packet received on an internal
         interface.";
    }

    container internal-src-port {
      description
        "Corresponds to the source port of the
         packet received on an internal interface.

         It is used also to carry the internal
         source ICMP identifier.";



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       uses port-number;
    }

    leaf external-src-address {
      type inet:ip-prefix;

      description
        "Source IP address/prefix of the packet sent
         on an external interface of the NAT.";
    }

    container external-src-port {
      description
        "Source port of the packet sent
         on an external interafce of the NAT.

         It is used also to carry the external
         source ICMP identifier.";
      uses port-number;
    }

    leaf internal-dst-address {
      type inet:ip-prefix;

      description
        "Corresponds to the destination IP address/prefix
         of the packet received on an internal interface
         of the NAT.

         For example, some NAT implementations support
         the translation of both source and destination
         addresses and ports, sometimes referred to
         as 'Twice NAT'.";
      }

    container internal-dst-port {
      description
        "Corresponds to the destination port of the
         IP packet received on the internal interface.

         It is used also to carry the internal
         destination ICMP identifier.";

      uses port-number;
    }

    leaf external-dst-address {
      type inet:ip-prefix;



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      description
        "Corresponds to the destination IP address/prefix
         of the packet sent on an external interface
         of the NAT.";
    }

    container external-dst-port {
      description
        "Corresponds to the destination port number of
         the packet sent on the external interface
         of the NAT.

         It is used also to carry the external
         destination ICMP identifier.";

      uses port-number;
    }

    leaf lifetime {
      type uint32;

      description
        "When specified, it tracks the connection that is
         fully-formed (e.g., once the 3WHS TCP is completed)
         or the duration for maintaining an explicit mapping
         alive. Static mappings may not be associated with a
         lifetime. If no lifetime is associated with a
         static mapping, an explicit action is requried to
         remove that mapping.";
    }
  }

 /*
  * NAT Module
  */

  container nat-module {
    description
      "NAT module";

    container nat-instances {
      description
        "NAT instances";

    list nat-instance {
      key "id";

      description



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        "A NAT instance.";

      leaf id {
        type uint32;

        description
          "NAT instance identifier.";

        reference
          "RFC 7659.";
      }

      leaf name {
        type string;

        description
         "A name associated with the NAT instance.";
      }

      leaf enable {
        type boolean;

        description
         "Status of the the NAT instance.";
      }

      container nat-capabilities {
        description
          "NAT capabilities";

        leaf-list nat-flavor {
          type identityref {
            base nat-type;
          }
          description
            "Type of NAT.";
        }

        leaf-list nat44-flavor {
          when "../nat-flavor = 'nat44'";

          type identityref {
            base nat44;
          }
          description
            "Type of NAT44: Basic NAT or NAPT.";
        }




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        leaf restricted-port-support {
          type boolean;

          description
            "Indicates source port NAT restriction
             support.";
        }

        leaf static-mapping-support {
          type boolean;

          description
            "Indicates whether static mappings are supported.";
        }

        leaf port-randomization-support {
          type boolean;

          description
            "Indicates whether port randomization is supported.";
        }

        leaf port-range-allocation-support {
          type boolean;

          description
            "Indicates whether port range allocation is supported.";
        }

        leaf port-preservation-suport {
          type boolean;

          description
            "Indicates whether port preservation is supported.";
        }

        leaf port-parity-preservation-support {
          type boolean;

          description
            "Indicates whether port parity preservation is supported.";
        }

        leaf address-roundrobin-support {
          type boolean;

          description
           "Indicates whether address allocation round robin is supported.";



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        }

        leaf paired-address-pooling-support {
          type boolean;

          description
            "Indicates whether paired-address-pooling is supported";
        }

        leaf endpoint-independent-mapping-support {
          type boolean;

          description
            "Indicates whether endpoint-independent-
             mapping in Section 4 of RFC 4787 is
             supported.";
        }

        leaf address-dependent-mapping-support {
          type boolean;

          description
            "Indicates whether address-dependent-mapping is supported.";
        }

        leaf address-and-port-dependent-mapping-support {
          type boolean;

          description
            "Indicates whether address-and-port-dependent-mapping is supported.";
        }

        leaf endpoint-independent-filtering-support {
          type boolean;

          description
            "Indicates whether endpoint-independent-filtering is supported.";
        }

        leaf address-dependent-filtering {
          type boolean;

        description
          "Indicates whether address-dependent-filtering is supported.";
        }

        leaf address-and-port-dependent-filtering {
          type boolean;



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          description
            "Indicates whether address-and-port-dependent is supported.";
        }
      }

      // Parameters for NAT pass through

      list nat-pass-through {
        key nat-pass-through-id;

        description
         "IP prefix NAT pass through.";

        leaf nat-pass-through-id {
          type uint32;

          description
            "An identifier of the IP prefix pass
             through.";
        }

        leaf nat-pass-through-pref {
          type inet:ip-prefix;

          description
            "The IP address subnets that match
             should not be translated. According to
             REQ#6 of RFC6888, it must be possible
             to administratively turn off translation
             for specific destination addresses
             and/or ports.";

          reference
            "REQ#6 of RFC6888.";
        }

        leaf nat-pass-through-port {
          type inet:port-number;

          description
            "The IP address subnets that match
             should not be translated. According to
             REQ#6 of RFC6888, it must be possible to
             administratively turn off translation
             for specific destination addresses
             and/or ports.";

          reference



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            "REQ#6 of RFC6888.";
        }
      }

      // NAT Policies: Multiple policies per NAT instance

     list nat-policy {
       key policy-id;

       description
         "NAT parameters for a given instance";

       leaf policy-id {
         type uint32;

         description
           "An identifier of the NAT policy.";
       }

       // CLAT Parameters
       container clat-parameters {
         description
           "CLAT parameters.";

         list clat-ipv6-prefixes {
           when "../../../nat-capabilities/nat-flavor = 'clat' ";

           key clat-ipv6-prefix;

           description
             "464XLAT double translation treatment is
              stateless when a dedicated /64 is available
              for translation on the CLAT. Otherwise, the
              CLAT will have both stateful and stateless
              since it requires NAT44 from the LAN to
              a single IPv4 address and then stateless
              translation to a single IPv6 address.";

            reference
              "RFC 6877.";

            leaf clat-ipv6-prefix {
              type inet:ipv6-prefix;

              description
                "An IPv6 prefix used for CLAT.";
            }
          }



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          list clat-ipv4-prefixes {
            when "../../../nat-capabilities/nat-flavor = 'clat'";

            key clat-ipv4-prefix;

            description
              "Pool of IPv4 addresses used for CLAT.
               192.0.0.0/29 is the IPv4 service continuity
               prefix.";

            reference
              "RFC 7335.";

            leaf clat-ipv4-prefix {
              type inet:ipv4-prefix;

              description
                "464XLAT double translation treatment is
                 stateless when a dedicated /64 is available
                 for translation on the CLAT.  Otherwise, the
                 CLAT will have both stateful and stateless
                 since it requires NAT44 from the LAN to
                 a single IPv4 address and then stateless
                 translation to a single IPv6 address.
                 The CLAT performs NAT44 for all IPv4 LAN
                 packets so that all the LAN-originated IPv4
                 packets appear from a single IPv4 address
                 and are then statelessly translated to one
                 interface IPv6 address that is claimed by
                 the CLAT.

                 An IPv4 address from this pool is also
                 provided to an application that makes
                 use of literals.";

             reference
               "RFC 6877.";
           }
         }
       }

       // NPTv6 Parameters

       list nptv6-prefixes {
         when "../../nat-capabilities/nat-flavor = 'nptv6' ";

         key translation-id;




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         description
           "Provides one or a list of (internal IPv6 prefix,
            external IPv6 prefix) required for NPTv6.

            In its simplest form, NPTv6 interconnects two network
            links, one of which is an 'internal' network link
            attachedto a leaf network within a single
            administrative domain and the other of which is an
            'external' network with connectivity to the global
            Internet.";

          reference
            "RFC 6296.";

          leaf translation-id {
            type uint32;

            description
            "An identifier of the NPTv6 prefixs.";
          }

          leaf internal-ipv6-prefix {
            type inet:ipv6-prefix;

            description
              "An IPv6 prefix used by an internal interface
               of NPTv6.";

            reference
              "RFC 6296.";
         }

         leaf external-ipv6-prefix {
           type inet:ipv6-prefix;

           description
             "An IPv6 prefix used by the external interface
              of NPTv6.";

           reference
             "RFC 6296.";
         }
       }

       // EAM SIIT Parameters

       list eam {
         when "../../nat-capabilities/nat-flavor = 'eam' ";



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         key eam-ipv4-prefix;

         description
           "The Explicit Address Mapping Table, a conceptual
            table in which each row represents an EAM.

            Each EAM describes a mapping between IPv4 and IPv6
            prefixes/addresses.";

         reference
           "Section 3.1 of RFC 7757.";

         leaf eam-ipv4-prefix {
           type inet:ipv4-prefix;

           description
             "The IPv4 prefix of an EAM.";

           reference
             "Section 3.2 of RFC 7757.";
         }

         leaf eam-ipv6-prefix {
           type inet:ipv6-prefix;

           description
             "The IPv6 prefix of an EAM.";

           reference
             "Section 3.2 of RFC 7757.";
         }
       }

       //NAT64 IPv6 Prefixes

       list nat64-prefixes {
         when "../../nat-capabilities/nat-flavor = 'nat64' " +
              " or ../../nat-capabilities/nat-flavor = 'clat'";

         key nat64-prefix;

         description
           "Provides one or a list of NAT64 prefixes
            with or without a list of destination IPv4 prefixes.

            Destination-based Pref64::/n is discussed in
            Section 5.1 of [RFC7050]). For example:
            192.0.2.0/24 is mapped to 2001:db8:122:300::/56.



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            198.51.100.0/24 is mapped to 2001:db8:122::/48.";

         reference
           "Section 5.1 of RFC7050.";

         leaf nat64-prefix {
           type inet:ipv6-prefix;
           //default "64:ff9b::/96";

           description
             "A NAT64 prefix. Can be NSP or a Well-Known
              Prefix (WKP).

              Organizations deploying stateless IPv4/IPv6
              translation should assign a Network-Specific
              Prefix to their IPv4/IPv6 translation service.

              For stateless NAT64, IPv4-translatable IPv6
              addresses must use the selected Network-Specific
              Prefix.  Both IPv4-translatable IPv6 addresses
              and IPv4-converted IPv6 addresses should use
              the same prefix.";

           reference
             "Sections 3.3 and 3.4 of RFC 6052.";
         }

         list destination-ipv4-prefix {
           key ipv4-prefix;

           description
             "An IPv4 prefix/address.";

           leaf ipv4-prefix {
             type inet:ipv4-prefix;
             description
               "An IPv4 address/prefix.";
            }
          }

          leaf stateless-enable {
            type boolean;

            description
              "Enable explicitly statless NAT64.";
         }
       }




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       list external-ip-address-pool {
         key pool-id;

         description
           "Pool of external IP addresses used to
            service internal hosts.

            Both contiguous and non-contiguous pools
            can be configured for NAT purposes.";

         leaf pool-id {
           type uint32;

           description
             "An identifier of the address pool.";
         }

         leaf external-ip-pool {
           type inet:ipv4-prefix;

           description
             "An IPv4 prefix used for NAT purposes.";
         }
       }

       container port-set-restrict {
         when "../../nat-capabilities/restricted-port-support = 'true'";

         description
           "Configures contiguous and non-contiguous port ranges.";

         uses port-set;
       }

       leaf dst-nat-enable {
         type boolean;
         default false;

         description
           "Enable/Disable destination NAT.
            A NAT44 may be configured to enable
            Destination NAT, too.";
        }

        list dst-ip-address-pool {
          when "../../nat-capabilities/nat-flavor = 'dst-nat' ";

          key pool-id;



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          description
            "Pool of IP addresses used for destination NAT.";

          leaf pool-id {
            type uint32;

            description
              "An identifier of the address pool.";
          }

          leaf dst-in-ip-pool {
            type inet:ip-prefix;

            description
              "Internal IP prefix/address";
          }

          leaf dst-out-ip-pool {
            type inet:ip-prefix;

            description
              "IP address/prefix used for destination NAT.";
          }
        }

        list supported-transport-protocols {
          key transport-protocol-id;

          description
            "Supported transport protocols.
             TCP and UDP are supported by default.";

          leaf transport-protocol-id {
            type uint8;
            mandatory true;

            description
              "Upper-layer protocol associated with this mapping.
               Values are taken from the IANA protocol registry.
               For example, this field contains 6 (TCP) for a TCP
               mapping or 17 (UDP) for a UDP mapping.";
          }

          leaf transport-protocol-name {
                 type string;
                 description
                  "For example, TCP, UDP, DCCP, and SCTP.";
          }



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        }

        leaf subscriber-mask-v6 {
          type uint8 {
            range "0 .. 128";
          }

          description
            "The subscriber-mask is an integer that indicates
             the length of significant bits to be applied on
             the source IP address (internal side) to
             unambiguously identify a CPE.

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

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

             Example: suppose the 2001:db8:100:100::/56 prefix
             is assigned to a NAT64 serviced CPE. Suppose also
             that 2001:db8:100:100::1 is the IPv6 address used
             by the client that resides in that CPE. When the
             NAT64 receives a packet from this client,
             it applies the subscriber-mask (e.g., 56) on
             the source IPv6 address to compute the associated
             prefix for this client (2001:db8:100:100::/56).
             Then, the NAT64 enforces policies based on that
             prefix (2001:db8:100:100::/56), not on the exact
             source IPv6 address.";
        }

        list subscriber-match {
          key sub-match-id;

          description
            "IP prefix match.";

          leaf sub-match-id {
            type uint32;

            description
              "An identifier of the subscriber masck.";
          }

          leaf sub-mask {



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            type inet:ip-prefix;
            mandatory true;

            description
              "The IP address subnets that match
               should be translated. E.g., all addresses
               that belong to the 192.0.2.0/24 prefix must
               be processed by the NAT.";
          }
        }

        leaf paired-address-pooling {
          type boolean;
          default true;

          description
            "Paired address pooling informs the NAT
             that all the flows from an internal IP
             address must be assigned the same external
             address.";

          reference
            "RFC 4007.";
        }

        leaf nat-mapping-type {
          type enumeration {
            enum "eim"  {
              description
                "endpoint-independent-mapping.";

              reference
                "Section 4 of RFC 4787.";
            }

            enum "adm"  {
              description
                "address-dependent-mapping.";

              reference
                "Section 4 of RFC 4787.";
            }

            enum "edm"  {
              description
                "address-and-port-dependent-mapping.";

              reference



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                "Section 4 of RFC 4787.";
            }
          }
          description
            "Indicates the type of a NAT mapping.";
        }

        leaf nat-filtering-type {
          type enumeration {
            enum "eif"  {
              description
                "endpoint-independent- filtering.";

              reference
                "Section 5 of RFC 4787.";
            }

            enum "adf"  {
              description
                "address-dependent-filtering.";

              reference
                "Section 5 of RFC 4787.";
            }

            enum "edf"  {
              description
                "address-and-port-dependent-filtering";

              reference
                "Section 5 of RFC 4787.";
            }
          }
            description
              "Indicates the type of a NAT filtering.";
        }

        list port-quota {
          when "../../nat-capabilities/nat44-flavor = "+
               "'napt' or "+
               "../../nat-capabilities/nat-flavor = "+
               "'nat64'";

          key quota-type;

          description
            "Configures a port quota to be assigned per
             subscriber. It corresponds to the maximum



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             number of ports to be used by a subscriber.";

          leaf port-limit {
            type uint16;

            description
              "Configures a port quota to be assigned per
               subscriber. It corresponds to the maximum
               number of ports to be used by a subscriber.";

            reference
              "REQ-4 of RFC 6888.";
          }

          leaf quota-type {
            type enumeration {
              enum "all"  {
                description
                  "The limit applies to all protocols.";

                reference
                  "REQ-4 of RFC 6888.";
              }

              enum "tcp"  {
                description
                  "TCP quota.";

                reference
                  "REQ-4 of RFC 6888.";
              }

              enum "udp"  {
                description
                  "UDP quota.";

                reference
                  "REQ-4 of RFC 6888.";
              }

              enum "icmp"  {
                description
                  "ICMP quota.";

                reference
                  "REQ-4 of RFC 6888.";
              }
            }



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              description
                "Indicates whether the port quota applies to
                 all protocols or to a specific transport.";
            }
          }

          leaf port-allocation-type {
            type enumeration {
              enum "random"  {
                description
                  "Port randomization is enabled.";
              }

              enum "port-preservation"  {
                description
                  "Indicates whether the NAT should
                   preserve the internal port number.";
              }

              enum "port-parity-preservation"  {
                description
                  "Indicates whether the NAT should
                   preserve the port parity of the
                   internal port number.";
              }

              enum "port-range-allocation"  {
                description
                  "Indicates whether the NAT assigns a
                   range of ports for an internal host.";
              }
            }
              description
                "Indicates the type of a port allocation.";
          }

          leaf address-roundrobin-enable {
            type boolean;

            description
              "Enable/disable address allocation
               round robin.";
          }

          container port-set {
            when "../port-allocation-type='port-range-allocation'";

            description



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              "Manages port-set assignments.";

            leaf port-set-size {
              type uint16;
              description
                "Indicates the size of assigned port
                 sets.";
            }

            leaf port-set-timeout {
              type uint32;
              description
                "Inactivty timeout for port sets.";
            }
          }

          container timers {
            description
              "Configure values of various timeouts.";

            leaf udp-timeout {
              type uint32;
              units "seconds";
              default 300;

              description
                "UDP inactivity timeout. That is the time a mapping
                 will stay active without packets traversing the NAT.";

              reference
                "RFC 4787.";
            }

            leaf tcp-idle-timeout {
              type uint32;
              units "seconds";
              default 7440;

              description
                "TCP Idle timeout should be
                 2 hours and 4 minutes.";

              reference
                "RFC 5382.";
            }

            leaf tcp-trans-open-timeout {
              type uint32;



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              units "seconds";
              default 240;

              description
                "The value of the transitory open connection
                 idle-timeout.

                 Section 2.1 of [RFC7857] clarifies that a NAT
                 should provide different configurable

                 parameters for configuring the open and
                 closing idle timeouts.

                 To accommodate deployments that consider
                 a partially open timeout of 4 minutes as being
                 excessive from a security standpoint, a NAT may
                 allow the configured timeout to be less than
                 4 minutes.

                 However, a minimum default transitory connection
                 idle-timeout of 4 minutes is recommended.";

              reference
                "Section 2.1 of RFC 7857.";
            }

            leaf tcp-trans-close-timeout {
              type uint32;
              units "seconds";
              default 240;

              description
                "The value of the transitory close connection
                idle-timeout.

                Section 2.1 of [RFC7857] clarifies that a NAT
                should provide different configurable
                parameters for configuring the open and
                closing idle timeouts.";

              reference
                "Section 2.1 of RFC 7857.";
            }

            leaf tcp-in-syn-timeout {
              type uint32;
              units "seconds";
              default 6;



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              description
                "A NAT must not respond to an unsolicited
                inbound SYN packet for at least 6 seconds
                after the packet is received.  If during
                this interval the NAT receives and translates
                an outbound SYN for the connection the NAT
                must silently drop the original unsolicited
                inbound SYN packet.";

             reference
                "RFC 5382.";
            }

            leaf fragment-min-timeout {
              type uint32;
              units "seconds";
              default 2;

              description
                "As long as the NAT has available resources,
                the NAT allows the fragments to arrive
                over fragment-min-timeout interval.
                The default value is inspired from RFC6146.";
            }

            leaf icmp-timeout {
              type uint32;
              units "seconds";
              default 60;

              description
                "An ICMP Query session timer must not expire
                 in less than 60 seconds. It is recommended
                 that the ICMP Query session timer be made
                 configurable";

              reference
                "RFC 5508.";
            }

            list per-port-timeout {
              key port-number;

              description
                "Some NATs are configurable with short timeouts
                 for some ports, e.g., as 10 seconds on
                 port 53 (DNS) and NTP (123) and longer timeouts
                 on other ports.";



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              leaf port-number {
                type inet:port-number;

                description
                  "A port number.";
              }

              leaf port-timeout {
                type inet:port-number;
                mandatory true;

                description
                  "Timeout for this port";
              }
            }

            leaf hold-down-timeout {
              type uint32;
              units "seconds";
              default 120;

              description
                "Hold down timer.

                 Ports in the hold down pool are not reassigned
                 until hold-down-timeout expires.

                 The length of time and the maximum
                 number of ports in this state must be
                 configurable by the administrator.
                 This is necessary in order
                 to prevent collisions between old
                 and new mappings and sessions. It ensures
                 that all established sessions are broken
                 instead of redirected to a different peer.";


              reference
                "REQ#8 of RFC 6888.";
            }

            leaf hold-down-max {
              type uint32;

              description
                "Maximum ports in the Hold down timer pool.

                 Ports in the hold down pool are not reassigned



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                 until hold-down-timeout expires.

                 The length of time and the maximum
                 number of ports in this state must be
                 configurable by the administrator.
                 This is necessary in order
                 to prevent collisions between old
                 and new mappings and sessions. It ensures
                 that all established sessions are broken
                 instead of redirected to a different peer.";

              reference
                "REQ#8 of RFC 6888.";
            }
          }

          list algs {

            key alg-name;

            description
              "ALG-related features.";

            leaf alg-name {
              type string;

              description
                "The name of the ALG";
            }

            leaf alg-transport-protocol {
              type uint32;

              description
                "The transport protocol used by the ALG.";
            }

            leaf alg-transport-port {
              type inet:port-number;

              description
                "The port number used by the ALG.";
            }

            leaf alg-status {
              type boolean;

              description



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                "Enable/disable the ALG.";
            }
          }

          leaf all-algs-enable {
            type boolean;

            description
             "Enable/disable all ALGs.";
          }

          container notify-pool-usage {
            description
              "Notification of pool usage when certain criteria
               are met.";

            leaf pool-id {
              type uint32;

              description
                "Pool-ID for which the notification
                 criteria is defined";
            }

            leaf notify-pool-hi-threshold {
              type percent;
              mandatory true;

              description
                "Notification must be generated when the
                 defined high threshold is reached.

                 For example, if a notification is
                 required when the pool utilization reaches
                 90%, this configuration parameter must
                 be set to 90%.";
            }

            leaf notify-pool-low-threshold {
              type percent;

              description
                "Notification must be generated when the defined
                 low threshold is reached.

                 For example, if a notification is required when
                 the pool utilization reaches below 10%,
                 this configuration parameter must be set to



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                 10%.";
            }
          }

          container external-realm {
            description
              "Identifies the external realm of the NAT.";


            choice realm-type {
              description
                "Interface or VRF.";

              case interface {
                description
                  "External interface.";

                leaf external-interface {
                  type if:interface-ref;

                  description
                    "Name of an external interface.";
                }
              }

              case vrf {
                description
                  "External VRF instance.";

                leaf external-vrf-instance {
                  type identityref {
                  base vrf-routing-instance;
                }
                  description
                    "A VRF instance.";
                }
              }
            }
          }
        } //nat-policy

        container mapping-limit {
          description
            "Information about the configuration parameters that
             limits the mappings based upon various criteria.";

          leaf limit-per-subscriber {
            type uint32;



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            description
              "Maximum number of NAT mappings per subscriber.";
          }

          leaf limit-per-vrf {
            type uint32;

            description
              "Maximum number of NAT mappings per VLAN/VRF.";
          }

          leaf limit-per-subnet {
            type inet:ip-prefix;

            description
              "Maximum number of NAT mappings per subnet.";
          }

          leaf limit-per-instance {
            type uint32;
            mandatory true;

            description
              "Maximum number of NAT mappings per instance.";
          }

          leaf limit-per-udp {
            type uint32;
            mandatory true;

            description
              "Maximum number of UDP NAT mappings per subscriber.";
          }

          leaf limit-per-tcp {
            type uint32;
            mandatory true;

            description
              "Maximum number of TCP NAT mappings per subscriber.";
          }

          leaf limit-per-icmp {
            type uint32;
            mandatory true;

            description
              "Maximum number of ICMP NAT mappings per subscriber.";



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          }
        }

        container connection-limit {
          description
            "Information about the configuration parameters that
             rate limit the translation based upon various
             criteria.";

          leaf limit-per-subscriber {
            type uint32;

            description
              "Rate-limit the number of new mappings
               and sessions per subscriber.";
          }

          leaf limit-per-vrf {
            type uint32;

            description
              "Rate-limit the number of new mappings
               and sessions per VLAN/VRF.";
          }

          leaf limit-per-subnet {
            type inet:ip-prefix;

            description
              "Rate-limit the number of new mappings
               and sessions per subnet.";
          }

          leaf limit-per-instance {
            type uint32;
            mandatory true;

            description
              "Rate-limit the number of new mappings
               and sessions per instance.";
          }

          leaf limit-per-udp {
            type uint32;
            mandatory true;

            description
              "Rate-limit the number of new UDP mappings



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               and sessions per subscriber.";
          }

          leaf limit-per-tcp {
            type uint32;
            mandatory true;

            description
              "Rate-limit the number of new TCP mappings
               and sessions per subscriber.";
          }

          leaf limit-per-icmp {
            type uint32;
            mandatory true;

            description
              "Rate-limit the number of new ICMP mappings
               and sessions per subscriber.";
          }
        }

        container logging-info {
          description
            "Information about logging NAT events";

          leaf logging-enable {
            type boolean;

            description
              "Enable logging features.";

            reference
              "Section 2.3 of RFC 6908.";
          }

          leaf destination-address {
            type inet:ip-prefix;
            mandatory true;

            description
              "Address of the collector that receives
               the logs";
          }

          leaf destination-port {
            type inet:port-number;
            mandatory true;



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            description
              "Destination port of the collector.";
          }

          choice protocol {

            description
              "Enable the protocol to be used for
               the retrieval of logging entries.";

            case syslog {
              leaf syslog {
                type boolean;

                description
                  "If SYSLOG is in use.";
              }
            }

            case ipfix {
              leaf ipfix {
                type boolean;

                description
                  "If IPFIX is in use.";
              }
            }

            case ftp {
              leaf ftp {
                type boolean;

                description
                  "If FTP is in use.";
              }
            }
          }
        }

        container mapping-table {
          when "../nat-capabilities/nat-flavor = "+
               "'nat44' or "+
               "../nat-capabilities/nat-flavor = "+
               "'nat64'or "+
               "../nat-capabilities/nat-flavor = "+
               "'clat'or "+
               "../nat-capabilities/nat-flavor = 'dst-nat'";




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          description
            "NAT mapping table. Applicable for functions
             which maintains static and/or dynamic mappings,
             such as NAT44, Destination NAT, NAT64, or CLAT.";

          list mapping-entry {
            key "index";

            description
              "NAT mapping entry.";

            uses mapping-entry;
          }
        }

        container statistics {

          config false;

          description
            "Statistics related to the NAT instance.";

          container traffic-statistics {
            description
              "Generic traffic statistics.";

            leaf sent-packet {
              type yang:zero-based-counter64;

              description
                "Number of packets sent.";
            }

            leaf sent-byte {
              type yang:zero-based-counter64;

              description
                "Counter for sent traffic in bytes.";
            }

            leaf rcvd-packet {
              type yang:zero-based-counter64;

              description
                "Number of received packets.";
            }

            leaf rcvd-byte {



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              type yang:zero-based-counter64;

              description
                "Counter for received traffic
                 in bytes.";
            }

            leaf dropped-packet {
              type yang:zero-based-counter64;

              description
                "Number of dropped packets.";
            }

            leaf dropped-byte {
              type yang:zero-based-counter64;

              description
                "Counter for dropped traffic in
                bytes.";
            }
          }

          container mapping-statistics {
            when "../../nat-capabilities/nat-flavor = "+
                 "'nat44' or "+
                 "../../nat-capabilities/nat-flavor = "+
                 "'nat64'or "+
                 "../../nat-capabilities/nat-flavor = 'dst-nat'";

           description
             "Mapping statistics.";

            leaf total-mappings {
              type uint32;

              description
                "Total number of NAT mappings present
                 at a given time. This variable includes
                 all the static and dynamic mappings.";
            }

            leaf total-tcp-mappings {
              type uint32;

              description
                "Total number of TCP mappings present
                at a given time.";



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            }

            leaf total-udp-mappings {
              type uint32;

              description
                "Total number of UDP mappings present
                 at a given time.";
            }

           leaf total-icmp-mappings {
             type uint32;

              description
                "Total number of ICMP mappings present
                at a given time.";
            }
          }

          container pool-stats {

            when "../../nat-capabilities/nat-flavor = "+
                 "'nat44' or "+
                 "../../nat-capabilities/nat-flavor = "+
                 "'nat64'";

            description
              "Statistics related to address/prefix
               pool usage";

            leaf pool-id {
              type uint32;

              description
                "Unique Identifier that represents
                 a pool of addresses/prefixes.";
            }

            leaf address-allocated {
              type uint32;

              description
                "Number of allocated addresses in
                 the pool";
            }

            leaf address-free {
              type uint32;



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              description
                "Number of unallocated addresses in
                 the pool at a given time.The sum of
                 unallocated and allocated
                 addresses is the total number of
                 addresses of the pool.";
            }

            container port-stats {

              description
                "Statistics related to port
                 usage.";

              leaf ports-allocated {
                type uint32;

                description
                  "Number of allocated ports
                   in the pool.";
              }

              leaf ports-free {
                type uint32;

                description
                  "Number of unallocated addresses
                   in the pool.";
              }
            }
          }
        }//statistics
      }
    }
  }

  /*
   * Notifications
   */

  notification nat-event {
    description
      "Notifications must be generated when the defined
       high/low threshold is reached. Related
       configuration parameters must be provided to
       trigger the notifications.";

    leaf id {



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      type leafref {
        path
             "/nat-module/nat-instances/"
              + "nat-instance/id";
                }
      description
        "NAT instance ID.";
    }

    leaf policy-id {
      type leafref {
        path
             "/nat-module/nat-instances/"
             + "nat-instance/nat-policy/policy-id";
      }

      description
        "Policy ID.";
    }

    leaf pool-id {
      type leafref {
        path
             "/nat-module/nat-instances/"
             + "nat-instance/nat-policy/"
             + "external-ip-address-pool/pool-id";
      }
      description
        "Pool ID.";
    }

    leaf notify-pool-threshold {
      type percent;
      mandatory true;

      description
        "A treshhold has been fired.";
    }
  }
}
<CODE ENDS>

4.  Security Considerations

   The YANG module defined in this memo is designed to be accessed via
   the NETCONF protocol [RFC6241].  The lowest NETCONF layer is the
   secure transport layer and the support of SSH is mandatory to
   implement secure transport [RFC6242].  The NETCONF access control



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   model [RFC6536] provides means to restrict access by some users to a
   pre-configured subset of all available NETCONF protocol operations
   and data.

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

5.  IANA Considerations

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

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


   This document requests IANA to register the following YANG module in
   the "YANG Module Names" registry [RFC7950].

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

6.  Acknowledgements

   Many thanks to Dan Wing and Tianran Zhou for the review.

   Thanks to Juergen Schoenwaelder for the comments on the YANG
   structure and the suggestion to use NMDA.

   Thanks to Lee Howard and Jordi Palet for the CLAT comments, Fred
   Baker for the NPTv6 comments, Tore Anderson for EAM SIIT review, and
   Kristian Poscic for the CGN review.

   Special thanks to Maros Marsalek and Marek Gradzki for sharing their
   comments based on the FD.io implementation of an earlier version of
   this module.

   Rajiv Asati suggested to clarify how the module applies for both
   stateless and stateful NAT64.






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7.  References

7.1.  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>.

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

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

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

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
              April 2011, <https://www.rfc-editor.org/info/rfc6146>.

   [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>.

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

   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation",
              RFC 6877, DOI 10.17487/RFC6877, April 2013,
              <https://www.rfc-editor.org/info/rfc6877>.





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

   [RFC7757]  Anderson, T. and A. Leiva Popper, "Explicit Address
              Mappings for Stateless IP/ICMP Translation", RFC 7757,
              DOI 10.17487/RFC7757, February 2016,
              <https://www.rfc-editor.org/info/rfc7757>.

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

   [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>.

7.2.  Informative References

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

   [I-D.ietf-behave-ipfix-nat-logging]
              Sivakumar, S. and R. Penno, "IPFIX Information Elements
              for logging NAT Events", draft-ietf-behave-ipfix-nat-
              logging-13 (work in progress), January 2017.

   [I-D.ietf-softwire-dslite-yang]
              Boucadair, M., Jacquenet, C., and S. Sivakumar, "YANG Data
              Modules for the DS-Lite", draft-ietf-softwire-dslite-
              yang-07 (work in progress), October 2017.

   [I-D.ietf-tsvwg-natsupp]
              Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control
              Transmission Protocol (SCTP) Network Address Translation
              Support", draft-ietf-tsvwg-natsupp-11 (work in progress),
              July 2017.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, DOI 10.17487/RFC2663, August 1999,
              <https://www.rfc-editor.org/info/rfc2663>.



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

   [RFC5597]  Denis-Courmont, R., "Network Address Translation (NAT)
              Behavioral Requirements for the Datagram Congestion
              Control Protocol", BCP 150, RFC 5597,
              DOI 10.17487/RFC5597, September 2009,
              <https://www.rfc-editor.org/info/rfc5597>.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              DOI 10.17487/RFC6052, October 2010,
              <https://www.rfc-editor.org/info/rfc6052>.

   [RFC6296]  Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
              Translation", RFC 6296, DOI 10.17487/RFC6296, June 2011,
              <https://www.rfc-editor.org/info/rfc6296>.

   [RFC6302]  Durand, A., Gashinsky, I., Lee, D., and S. Sheppard,
              "Logging Recommendations for Internet-Facing Servers",
              BCP 162, RFC 6302, DOI 10.17487/RFC6302, June 2011,
              <https://www.rfc-editor.org/info/rfc6302>.

   [RFC6736]  Brockners, F., Bhandari, S., Singh, V., and V. Fajardo,
              "Diameter Network Address and Port Translation Control
              Application", RFC 6736, DOI 10.17487/RFC6736, October
              2012, <https://www.rfc-editor.org/info/rfc6736>.

   [RFC6887]  Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
              P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              DOI 10.17487/RFC6887, April 2013,
              <https://www.rfc-editor.org/info/rfc6887>.

   [RFC7289]  Kuarsingh, V., Ed. and J. Cianfarani, "Carrier-Grade NAT
              (CGN) Deployment with BGP/MPLS IP VPNs", RFC 7289,
              DOI 10.17487/RFC7289, June 2014,
              <https://www.rfc-editor.org/info/rfc7289>.

   [RFC7335]  Byrne, C., "IPv4 Service Continuity Prefix", RFC 7335,
              DOI 10.17487/RFC7335, August 2014,
              <https://www.rfc-editor.org/info/rfc7335>.

   [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>.



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   [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>.

   [RFC7659]  Perreault, S., Tsou, T., Sivakumar, S., and T. Taylor,
              "Definitions of Managed Objects for Network Address
              Translators (NATs)", RFC 7659, DOI 10.17487/RFC7659,
              October 2015, <https://www.rfc-editor.org/info/rfc7659>.

   [RFC7753]  Sun, Q., Boucadair, M., Sivakumar, S., Zhou, C., Tsou, T.,
              and S. Perreault, "Port Control Protocol (PCP) Extension
              for Port-Set Allocation", RFC 7753, DOI 10.17487/RFC7753,
              February 2016, <https://www.rfc-editor.org/info/rfc7753>.

   [RFC8045]  Cheng, D., Korhonen, J., Boucadair, M., and S. Sivakumar,
              "RADIUS Extensions for IP Port Configuration and
              Reporting", RFC 8045, DOI 10.17487/RFC8045, January 2017,
              <https://www.rfc-editor.org/info/rfc8045>.

Appendix A.  Sample Examples

   This section provides a non-exhaustive set of examples to illustrate
   the use of the NAT YANG module.

A.1.  Traditional NAT44

   Traditional NAT44 is a Basic NAT44 or NAPT that is used to share the
   same IPv4 address among hosts that are owned by the same subscriber.
   This is typically the NAT that is embedded in CPE devices.

   This NAT is usually provided with one single external IPv4 address;
   disambiguating connections is achieved by rewriting the source port
   number.  The XML snippet to configure the external IPv4 address in
   such case together with a mapping entry is depicted below:















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   <nat-instances>
        <nat-instance>
          <id>1</id>
          <name>NAT_Subscriber_A</name>
           ....
          <external-ip-address-pool>
              <pool-id>1</pool-id>
              <external-ip-pool>
                 192.0.2.1
              </external-ip-pool>
          </external-ip-address-pool>
           ....
          <mapping-table>
              ....
              <external-src-address>
                 192.0.2.1
              </external-src-address>
              ....
          <mapping-table>
        </nat-instance>
   </nat-instances>


   The following shows the XML excerpt depicting a dynamic UDP mapping
   entry maintained by a traditional NAT44.  In reference to this
   example, the UDP packet received with a source IPv4 address
   (192.0.2.1) and source port number (1568) is translated into a UDP
   packet having a source IPv4 address (198.51.100.1) and source port
   (15000).  The lifetime of this mapping is 300 seconds.






















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   <mapping-entry>
     <index>15</index>
     <type>
        dynamic-explicit
     </type>
     <transport-protocol>
        17
     </transport-protocol>
     <internal-src-address>
        192.0.2.1
     </internal-dst-address>
     <internal-src-port>
        <start-port-number>
           1568
        </start-port-number>
     </internal-dst-port>
     <external-dst-address>
        198.51.100.1
     </external-dst-address>
     <external-dst-port>
        <start-port-number>
           15000
        </start-port-number>
     </external-dst-port>
     <lifetime>
        300
     </lifetime>
   </mapping-entry>

A.2.  CGN

   The following XML snippet shows the example of the capabilities
   supported by a CGN as retrieved using NETCONF.


















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   <nat-capabilities
     <nat-flavor>
      nat44
     </nat44-flavor>
     <restricted-port-support>
      false
     </restricted-port-support>
     <static-mapping-support>
       true
     </static-mapping-support>
     <port-randomization-support>
       true
     </port-randomization-support>
     <port-range-allocation-support>
       true
     </port-range-allocation-support>
     <port-preservation-suport>
       true
     </port-preservation-suport>
     <port-parity-preservation-support>
       false
     </port-parity-preservation-support>
     <address-roundrobin-support>
       true
     </address-roundrobin-support>
     <paired-address-pooling-support>
       true
     </paired-address-pooling-support>
     <endpoint-independent-mapping-support>
       true
     </endpoint-independent-mapping-support>
     <address-dependent-mapping-support>
       false
     </address-dependent-mapping-support>
     <address-and-port-dependent-mapping-support>
       false
     </address-and-port-dependent-mapping-support>
     <endpoint-independent-filtering-support>
       true
     </endpoint-independent-filtering-support>
     <address-dependent-filtering>
       false
     </address-dependent-filtering>
     <address-and-port-dependent-filtering>
       false
     </address-and-port-dependent-filtering>
   </nat-capabilities>




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   The following XML snippet shows the example of a CGN that is
   provisioned with one contiguous pool of external IPv4 addresses
   (192.0.2.0/24).  Further, the CGN is instructed to limit the number
   of allocated ports per subscriber to 1024.  Ports can be allocated by
   the CGN by assigning ranges of 256 ports (that is, a subscriber can
   be allocated up to four port ranges of 256 ports each).

   <nat-instances>
        <nat-instance>
          <id>1</id>
          <name>myCGN</name>
           ....
          <external-ip-address-pool>
              <pool-id>1</pool-id>
              <external-ip-pool>
                  192.0.2.0/24
              </external-ip-pool>
          </external-ip-address-pool>
          <port-quota>
            <port-limit>
              1024
            </port-limit>
            <quota-type >
              all
            </quota-type >
          </port-quota>
          <port-allocation-type>
              port-range-allocation
          </port-allocation-type>
          <port-set>
             <port-set-size>
                256
             </port-set-size>
          </port-set>
           ....
        </nat-instance>
   </nat-instances>

   An administrator may decide to allocate one single port range per
   subscriber (port range of 1024 ports) as shown below:











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   <nat-instances>
        <nat-instance>
          <id>1</id>
          <name>myotherCGN</name>
           ....
          <external-ip-address-pool>
              <pool-id>1</pool-id>
              <external-ip-pool>
                  192.0.2.0/24
              </external-ip-pool>
          </external-ip-address-pool>
          <port-quota>
            <port-limit>
              1024
            </port-limit>
            <quota-type >
              all
            </quota-type >
          </port-quota>
          <port-allocation-type>
              port-range-allocation
          </port-allocation-type>
          <port-set>
             <port-set-size>
                  1024
             </port-set-size>
             ....
          </port-set>
           ....
        </nat-instance>
   </nat-instances>


A.3.  CGN Pass-Through

   Figure 1 illustrates an example of the CGN pass-through feature.

                     X1:x1            X1':x1'            X2:x2
                     +---+from X1:x1  +---+from X1:x1    +---+
                     | C |  to X2:x2  |   |  to X2:x2    | S |
                     | l |>>>>>>>>>>>>| C |>>>>>>>>>>>>>>| e |
                     | i |            | G |              | r |
                     | e |<<<<<<<<<<<<| N |<<<<<<<<<<<<<<| v |
                     | n |from X2:x2  |   |from X2:x2    | e |
                     | t |  to X1:x1  |   |  to X1:x1    | r |
                     +---+            +---+              +---+

                        Figure 1: CGN Pass-Through



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   For example, in order to disable NAT for communications issued by the
   client (192.0.2.25), the following configuration parameter must be
   set:

   <nat-pass-through>
        ...
        <nat-pass-through-pref>192.0.2.25</nat-pass-through-pref>
        ...
   </nat-pass-through>

A.4.  NAT64

   Let's consider the example of a NAT64 that should use
   2001:db8:122:300::/56 to perform IPv6 address synthesis [RFC6052].
   The XML snippet to configure the NAT64 prefix in such case is
   depicted below:

   <nat64-prefixes>
      <nat64-prefix>
        2001:db8:122:300::/56
      </nat64-prefix>
   </nat64-prefixes>

   A NAT64 can be instructed to behave in the stateless mode by
   providing the following configuration.  The same NAT64 prefix is used
   for constructing both IPv4- translatable IPv6 addresses and
   IPv4-converted IPv6 addresses (Section 3.3 of [RFC6052]).

   <nat64-prefixes>
      <nat64-prefix>
        2001:db8:122:300::/56
      </nat64-prefix>
      <stateless-enable>
       true
      </stateless-enable>
   </nat64-prefixes>

   Let's now consider the example of a NAT64 that should use
   2001:db8:122::/48 to perform IPv6 address synthesis [RFC6052] only if
   the destination address matches 198.51.100.0/24.  The XML snippet to
   configure the NAT64 prefix in such case is shown below:










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   <nat64-prefixes>
      <nat64-prefix>
         2001:db8:122::/48
      </nat64-prefix>
      <destination-ipv4-prefix>
         <ipv4-prefix>
             198.51.100.0/24
         </ipv4-prefix>
      </destination-ipv4-prefix>
   </nat64-prefixes>

A.5.  Explicit Address Mappings for Stateless IP/ICMP Translation

   As specified in [RFC7757], an EAM consists of an IPv4 prefix and an
   IPv6 prefix.  Let's consider the set of EAM examples in Figure 2.

                  +---+----------------+----------------------+
                  | # |  IPv4 Prefix   |     IPv6 Prefix      |
                  +---+----------------+----------------------+
                  | 1 | 192.0.2.1      | 2001:db8:aaaa::      |
                  | 2 | 192.0.2.2/32   | 2001:db8:bbbb::b/128 |
                  | 3 | 192.0.2.16/28  | 2001:db8:cccc::/124  |
                  | 4 | 192.0.2.128/26 | 2001:db8:dddd::/64   |
                  | 5 | 192.0.2.192/29 | 2001:db8:eeee:8::/62 |
                  | 6 | 192.0.2.224/31 | 64:ff9b::/127        |
                  +---+----------------+----------------------+

                     Figure 2: EAM Examples (RFC7757)

   The following XML excerpt illustrates how these EAMs can be
   configured using the YANG NAT module:




















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   <eam>
     <eam-ipv4-prefix>
        192.0.2.1
     </eam-ipv4-prefix>
     <eam-ipv6-prefix>
        2001:db8:aaaa::
     </eam-ipv6-prefix>
   </eam>
   <eam>
     <eam-ipv4-prefix>
        192.0.2.2/32
     </eam-ipv4-prefix>
     <eam-ipv6-prefix>
        2001:db8:bbbb::b/128
     </eam-ipv6-prefix>
   </eam>
   <eam>
     <eam-ipv4-prefix>
        192.0.2.16/28
     </eam-ipv4-prefix>
     <eam-ipv6-prefix>
        2001:db8:cccc::/124
     </eam-ipv6-prefix>
   </eam>
   <eam>
     <eam-ipv4-prefix>
        192.0.2.128/26
     </eam-ipv4-prefix>
     <eam-ipv6-prefix>
        2001:db8:dddd::/64
     </eam-ipv6-prefix>
   </eam>
   <eam>
     <eam-ipv4-prefix>
        192.0.2.192/29
     </eam-ipv4-prefix>
     <eam-ipv6-prefix>
        2001:db8:eeee:8::/62
     </eam-ipv6-prefix>
   </eam>
   <eam>
     <eam-ipv4-prefix>
        192.0.2.224/31
     </eam-ipv4-prefix>
     <eam-ipv6-prefix>
        64:ff9b::/127
     </eam-ipv6-prefix>
   </eam>



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   EAMs may be enabled jointly with statefull NAT64.  This example shows
   a NAT64 fucntion that supports static mappings:

   <nat-capabilities
     <nat-flavor>
      nat64
     </nat44-flavor>
     <static-mapping-support>
       true
     </static-mapping-support>
     <port-randomization-support>
       true
     </port-randomization-support>
     <port-range-allocation-support>
       true
     </port-range-allocation-support>
     <port-preservation-suport>
       true
     </port-preservation-suport>
     <port-parity-preservation-support>
       false
     </port-parity-preservation-support>
     <address-roundrobin-support>
       true
     </address-roundrobin-support>
     <paired-address-pooling-support>
       true
     </paired-address-pooling-support>
     <endpoint-independent-mapping-support>
       true
     </endpoint-independent-mapping-support>
     <address-dependent-mapping-support>
       false
     </address-dependent-mapping-support>
     <address-and-port-dependent-mapping-support>
       false
     </address-and-port-dependent-mapping-support>
     <endpoint-independent-filtering-support>
       true
     </endpoint-independent-filtering-support>
     <address-dependent-filtering>
       false
     </address-dependent-filtering>
     <address-and-port-dependent-filtering>
       false
     </address-and-port-dependent-filtering>
   </nat-capabilities>




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A.6.  Static Mappings with Port Ranges

   The following example shows a static mapping that instructs a NAT to
   translate packets issued from 192.0.2.1 and with source ports in the
   100-500 range to 198.51.100.1:1100-1500.

   <mapping-entry>
     <index>1</index>
     <type>static</type>
     <transport-protocol>6</transport-protocol>
     <internal-src-address>
        192.0.2.1
     </internal-dst-address>
     <internal-dst-port>
       <start-port-number>
          100
       </start-port-number>
       <end-port-number>
         500
       </end-port-number>
     </internal-dst-port>
     <external-src-address>
        198.51.100.1
     </external-dst-address>
     <external-src-port>
        <start-port-number>
          1100
        </start-port-number>
        <end-port-number>
          1500
        </end-port-number>
     </external-dst-port>
     ...
   </mapping-entry>

A.7.  Static Mappings with IP Prefixes

   The following example shows a static mapping that instructs a NAT to
   translate packets issued from 192.0.2.1/24 to 198.51.100.1/24.












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   <mapping-entry>
     <index>1</index>
     <type>static</type>
     <transport-protocol>6</transport-protocol>
     <internal-src-address>
        192.0.2.1/24
     </internal-dst-address>
     <external-src-address>
        198.51.100.1/24
     </external-dst-address>
     ...
   </mapping-entry>

A.8.  Destination NAT

   The following XML snippet shows an example a destination NAT that is
   instructed to translate packets having 192.0.2.1 as a destination IP
   address to 198.51.100.1.

   <dst-ip-address-pool>
      <pool-id>1</pool-id>
      <dst-in-ip-pool>
        192.0.2.1
      </dst-in-ip-pool>
      <dst-out-ip-pool>
        198.51.100.1
      </dst-out-ip-pool>
   </dst-ip-address-pool>

   In order to instruct a NAT to translate TCP packets destined to
   192.0.2.1:80 to 198.51.100.1:8080, the following XML snippet shows
   the static mapping to be configured on the NAT:



















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   <mapping-entry>
     <index>1</index>
     <type>static</type>
     <transport-protocol>6</transport-protocol>
     <internal-dst-address>
        192.0.2.1
     </internal-dst-address>
     <internal-dst-port>
         <start-port-number>80</start-port-number>
     </internal-dst-port>
     <external-dst-address>
         198.51.100.1
     </external-dst-address>
     <external-dst-port>
         <start-port-number>8080</start-port-number>
     </external-dst-port>
   </mapping-entry>

   In order to instruct a NAT to translate TCP packets destined to
   192.0.2.1:80 (http traffic) to 198.51.100.1 and 192.0.2.1:22 (ssh
   traffic) to 198.51.100.2, the following XML snippet shows the static
   mappings to be configured on the NAT:





























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   <mapping-entry>
     <index>1</index>
     <type>static</type>
     <transport-protocol>6</transport-protocol>
     <internal-dst-address>
       192.0.2.1
     </internal-dst-address>
     <internal-dst-port>
       <start-port-number>
         80
       </start-port-number>
     </internal-dst-port>
     <external-dst-address>
       198.51.100.1
     </external-dst-address>
     ...
   </mapping-entry>
   <mapping-entry>
     <index>2</index>
     <type>static</type>
     <transport-protocol>
        6
     </transport-protocol>
     <internal-dst-address>
       192.0.2.1
     </internal-dst-address>
     <internal-dst-port>
       <start-port-number>
         22
       </start-port-number>
     </internal-dst-port>
     <external-dst-address>
       198.51.100.2
     </external-dst-address>
     ...
   </mapping-entry>


   The NAT may also be instructed to proceed with both source and
   destination NAT.  To do so, in addition to the above sample to
   configure destination NAT, the NAT may be provided, for example with
   a pool of external IP addresses (198.51.100.0/24) to use for source
   address translation.  An example of the corresponding XML snippet is
   provided hereafter:







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   <external-ip-address-pool>
     <pool-id>1</pool-id>
     <external-ip-pool>
        198.51.100.0/24
     </external-ip-pool>
   </external-ip-address-pool>

   Instead of providing an external IP address to share, the NAT may be
   configured with static mapping entries that modifies the internal IP
   address and/or port number.

A.9.  CLAT

   The following XML snippet shows the example of a CLAT that is
   configured with 2001:db8:1234::/96 as PLAT-side IPv6 prefix and
   2001:db8:aaaa::/96 as CLAT-side IPv6 prefix.  The CLAT is also
   provided with 192.0.0.1/32 (which is selected from the IPv4 service
   continuity prefix defined in [RFC7335]).

   <clat-ipv6-prefixes>
      <clat-ipv6-prefix>
        2001:db8:aaaa::/96
      </clat-ipv6-prefix>
   </clat-ipv6-prefixes>
   <clat-ipv4-prefixes>
      <clat-ipv4-prefix>
        192.0.0.1/32
      </clat-ipv4-prefix>
   </clat-ipv4-prefixes>
   <nat64-prefixes>
      <nat64-prefix>
        2001:db8:1234::/96
      </nat64-prefix>
   </nat64-prefixes>


A.10.  NPTv6

   Let's consider the example of a NPTv6 translator that should rewrite
   packets with the source prefix (fd01:203:405:/48) with the external
   prefix (2001:db8:1:/48).  The internal interface is "eth0" while the
   external interface is "eth1".









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                  External Network:  Prefix = 2001:db8:1:/48
                      --------------------------------------
                                        |
                                        |eth1
                                 +-------------+
                             eth4|     NPTv6   |eth2
                         ...-----|             |------...
                                 +-------------+
                                        |eth0
                                        |
                      --------------------------------------
                  Internal Network:  Prefix = fd01:203:405:/48

                        Example of NPTv6 (RFC6296)

   The XML snippet to configure NPTv6 prefixes in such case is depicted
   below:

   <nptv6-prefixes>
     <translation-id>1</translation-id>
     <internal-ipv6-prefix>
       fd01:203:405:/48
     </internal-ipv6-prefix>
     <external-ipv6-prefix>
       2001:db8:1:/48
     </external-ipv6-prefix>
   </nptv6-prefixes>
   ...
   <external-interfaces>
    <external-interface>
      eth1
    </external-interface>
   </external-interfaces>


   Figure 3 shows an example of an NPTv6 that interconnects two internal
   networks (fd01:203:405:/48 and fd01:4444:5555:/48); each is
   translated using a dedicated prefix (2001:db8:1:/48 and
   2001:db8:6666:/48, respectively).












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                     Internal Prefix = fd01:4444:5555:/48
                     --------------------------------------
                          V            |      External Prefix
                          V            |eth1     2001:db8:1:/48
                          V        +---------+      ^
                          V        |  NPTv6  |      ^
                          V        |         |      ^
                          V        +---------+      ^
                 External Prefix       |eth0        ^
                 2001:db8:6666:/48     |            ^
                     --------------------------------------
                     Internal Prefix = fd01:203:405:/48

             Figure 3: Connecting two Peer Networks (RFC6296)

   To that aim, the following configuration is provided to the NPTv6:

   <nat-policy>
    <policy-id>1</policy-id>
    <nptv6-prefixes>
     <translation-id>1</translation-id>
     <internal-ipv6-prefix>
       fd01:203:405:/48
     </internal-ipv6-prefix>
     <external-ipv6-prefix>
       2001:db8:1:/48
     </external-ipv6-prefix>
     </nptv6-prefixes>
      <external-interface>
       eth1
      </external-interface>
   </nat-policy>
   <nat-policy>
    <policy-id>2</policy-id>
    <nptv6-prefixes>
     <translation-id>2</translation-id>
     <internal-ipv6-prefix>
         fd01:4444:5555:/48
     </internal-ipv6-prefix>
     <external-ipv6-prefix>
         2001:db8:6666:/48
     </external-ipv6-prefix>
    </nptv6-prefixes>
    <external-interface>
      eth0
    </external-interface>
   </nat-policy>




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Authors' Addresses

   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Senthil Sivakumar
   Cisco Systems
   7100-8 Kit Creek Road
   Research Triangle Park, North Carolina  27709
   USA

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


   Christian Jacquenet
   Orange
   Rennes  35000
   France

   Email: christian.jacquenet@orange.com


   Suresh Vinapamula
   Juniper Networks
   1133 Innovation Way
   Sunnyvale  94089
   USA

   Email: sureshk@juniper.net


   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: bill.wu@huawei.com







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