ietf-nat

This module is a YANG module for NAT implementations. NAT44, Network Address and Protocol Translation from IPv6 Clients to IPv4 ...

  • Version: 2019-01-10

    ietf-nat@2019-01-10


    
      module ietf-nat {
    
        yang-version 1.1;
    
        namespace
          "urn:ietf:params:xml:ns:yang:ietf-nat";
    
        prefix nat;
    
        import ietf-inet-types {
          prefix inet;
          reference
            "Section 4 of RFC 6991";
    
    
        }
        import ietf-yang-types {
          prefix yang;
          reference
            "Section 3 of RFC 6991";
    
    
        }
        import ietf-interfaces {
          prefix if;
          reference
            "RFC 8343: A YANG Data Model for Interface Management";
    
    
        }
    
        organization
          "IETF OPSAWG (Operations and Management Area Working Group)";
    
        contact
          "WG Web:   <https://datatracker.ietf.org/wg/opsawg/>
    WG List:  <mailto:opsawg@ietf.org>
    
    Editor:  Mohamed Boucadair
    	 <mailto:mohamed.boucadair@orange.com>
    
    Author:  Senthil Sivakumar
    	 <mailto:ssenthil@cisco.com>
    
    Author:  Christian Jacquenet
    	 <mailto:christian.jacquenet@orange.com>
    
    Author:  Suresh Vinapamula
    	 <mailto:sureshk@juniper.net>
    
    Author:  Qin Wu
    	 <mailto:bill.wu@huawei.com>";
    
        description
          "This module is a YANG module for NAT implementations.
    NAT44, Network Address and Protocol Translation from IPv6
    Clients to IPv4 Servers (NAT64), customer-side translator
    (CLAT), Stateless IP/ICMP Translation (SIIT), Explicit
    Address Mappings (EAM) for SIIT, IPv6 Network Prefix
    Translation (NPTv6), and Destination NAT are covered.
    
    Copyright (c) 2018 IETF Trust and the persons identified as
    authors of the code.  All rights reserved.
    
    Redistribution and use in source and binary forms, with or
    without modification, is permitted pursuant to, and subject
    to the license terms contained in, the Simplified BSD License
    set forth in Section 4.c of the IETF Trust's Legal Provisions
    Relating to IETF Documents
    (http://trustee.ietf.org/license-info).
    
    This version of this YANG module is part of RFC 8512; see
    the RFC itself for full legal notices.";
    
        revision "2019-01-10" {
          description "Initial revision.";
          reference
            "RFC 8512: A YANG Module for Network Address Translation
            	  (NAT) and Network Prefix Translation (NPT)";
    
        }
    
    
        typedef percent {
          type uint8 {
            range "0 .. 100";
          }
          description "Percentage";
        }
    
        feature basic-nat44 {
          description
            "Basic NAT44 translation is limited to IP addresses alone.";
          reference
            "RFC 3022: Traditional IP Network Address Translator
            	  (Traditional NAT)";
    
        }
    
        feature napt44 {
          description
            "Network Address Port Translator (NAPT): translation is
    extended to include IP addresses and transport identifiers
    (such as a TCP/UDP port or ICMP query ID).
    
    If the internal IP address is not sufficient to uniquely
    disambiguate NAPT44 mappings, an additional attribute is
    required.  For example, that additional attribute may
    be an IPv6 address (a.k.a., DS-Lite) or
    a Layer 2 identifier (a.k.a., Per-Interface NAT)";
          reference
            "RFC 3022: Traditional IP Network Address Translator
            	  (Traditional NAT)";
    
        }
    
        feature dst-nat {
          description
            "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.";
        }
    
        feature nat64 {
          description
            "NAT64 translation allows IPv6-only clients to contact IPv4
    servers using, e.g., UDP, TCP, or ICMP.  One or more
    public IPv4 addresses assigned to a NAT64 translator are
    shared among several IPv6-only clients.";
          reference
            "RFC 6146: Stateful NAT64: Network Address and Protocol
            	  Translation from IPv6 Clients to IPv4 Servers";
    
        }
    
        feature siit {
          description
            "The Stateless IP/ICMP Translation Algorithm (SIIT), which
    translates between IPv4 and IPv6 packet headers (including
    ICMP headers).
    
    In the stateless mode, an IP/ICMP translator converts IPv4
    addresses to IPv6, and vice versa, solely based on the
    configuration of the stateless IP/ICMP translator and
    information contained within the packet being translated.
    The translator must support the stateless address mapping
    algorithm defined in RFC 6052, which is the default behavior.";
          reference
            "RFC 7915: IP/ICMP Translation Algorithm";
    
        }
    
        feature clat {
          description
            "CLAT is customer-side translator that algorithmically
    translates 1:1 private IPv4 addresses to global IPv6
    addresses, and vice versa.
    
    When a dedicated /64 prefix is not available for translation
    from DHCPv6-PD, the CLAT may perform 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 via
    the Neighbor Discovery Protocol (NDP) and defended with
    Duplicate Address Detection.";
          reference
            "RFC 6877: 464XLAT: Combination of Stateful and
            	  Stateless Translation";
    
        }
    
        feature eam {
          description
            "Explicit Address Mapping (EAM) is a bidirectional coupling
    between an IPv4 prefix and an IPv6 prefix.";
          reference
            "RFC 7757: Explicit Address Mappings for Stateless IP/ICMP
            	  Translation";
    
        }
    
        feature nptv6 {
          description
            "NPTv6 is a stateless transport-agnostic IPv6-to-IPv6
    prefix translation.";
          reference
            "RFC 6296: IPv6-to-IPv6 Network Prefix Translation";
    
        }
    
        identity nat-type {
          description
            "Base identity for nat type.";
        }
    
        identity basic-nat44 {
          base nat:nat-type;
          description
            "Identity for Basic NAT support.";
          reference
            "RFC 3022: Traditional IP Network Address Translator
            	  (Traditional NAT)";
    
        }
    
        identity napt44 {
          base nat:nat-type;
          description
            "Identity for NAPT support.";
          reference
            "RFC 3022: Traditional IP Network Address Translator
            	  (Traditional NAT)";
    
        }
    
        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: Stateful NAT64: Network Address and Protocol
            	  Translation from IPv6 Clients to IPv4 Servers";
    
        }
    
        identity siit {
          base nat:nat-type;
          description
            "Identity for SIIT support.";
          reference
            "RFC 7915: IP/ICMP Translation Algorithm";
    
        }
    
        identity clat {
          base nat:nat-type;
          description
            "Identity for CLAT support.";
          reference
            "RFC 6877: 464XLAT: Combination of Stateful and Stateless
            	  Translation";
    
        }
    
        identity eam {
          base nat:nat-type;
          description
            "Identity for EAM support.";
          reference
            "RFC 7757: Explicit Address Mappings for Stateless IP/ICMP
            	  Translation";
    
        }
    
        identity nptv6 {
          base nat:nat-type;
          description
            "Identity for NPTv6 support.";
          reference
            "RFC 6296: IPv6-to-IPv6 Network Prefix Translation";
    
        }
    
        grouping port-number {
          description
            "An individual port number or a range of ports.
    When only start-port-number is present,
    it represents a single port number.";
          leaf start-port-number {
            type inet:port-number;
            description
              "Beginning 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";
    
          }
        }  // grouping port-number
    
        grouping port-set {
          description
            "Indicates a set of port numbers.
    
    It may be a simple port range, or use the Port Set
    Identifier (PSID) algorithm to represent a range of
    transport-layer port numbers that will be used by a
    NAPT.";
          choice port-type {
            default "port-range";
            description
              "Port type: port-range or port-set-algo.";
            reference
              "RFC 7597: Mapping of Address and Port with
              	  Encapsulation (MAP-E)";
    
            case port-range {
              uses port-number;
            }  // case port-range
    
            case port-set-algo {
              leaf psid-offset {
                type uint8 {
                  range "0..15";
                }
                description
                  "The number of offset bits (a.k.a., 'a' bits).
    Specifies the numeric value for the excluded port
    range/offset bits.
    
    Allowed values are between 0 and 15.";
                reference
                  "Section 5.1 of RFC 7597";
    
              }
    
              leaf psid-len {
                type uint8 {
                  range "0..15";
                }
                mandatory true;
                description
                  "The length of PSID, representing the sharing
    ratio for an IPv4 address.
    
    (also known as 'k').
    
    The address-sharing ratio would be 2^k.";
                reference
                  "Section 5.1 of RFC 7597";
    
              }
    
              leaf psid {
                type uint16;
                mandatory true;
                description
                  "PSID value, which identifies a set
    of ports algorithmically.";
                reference
                  "Section 5.1 of RFC 7597";
    
              }
            }  // case port-set-algo
          }  // choice port-type
        }  // grouping port-set
    
        grouping mapping-entry {
          description
            "NAT mapping entry.
    
    If an attribute is not stored in the mapping/session table,
    it means the corresponding field of a packet that
    matches this entry is not rewritten by the NAT or this
    information is not required for NAT filtering purposes.";
          leaf index {
            type uint32;
            description
              "A unique identifier of a mapping entry.  This identifier
    can be automatically assigned by the NAT instance or be
    explicitly configured.";
          }
    
          leaf type {
            type enumeration {
              enum "static" {
                value 0;
                description
                  "The mapping entry is explicitly configured
    (e.g., via a command-line interface).";
              }
              enum "dynamic-implicit" {
                value 1;
                description
                  "This mapping is created implicitly as a side effect
    of processing a packet that requires a new mapping.";
              }
              enum "dynamic-explicit" {
                value 2;
                description
                  "This mapping is created as a result of an explicit
    request, e.g., a PCP message.";
              }
            }
            description
              "Indicates the type of a mapping entry.  For example,
    a mapping can be: static, implicit dynamic,
    or explicit dynamic.";
          }
    
          leaf transport-protocol {
            type uint8;
            description
              "The upper-layer protocol associated with this mapping.
    Values are taken from the IANA Protocol Numbers registry:
    <https://www.iana.org/assignments/protocol-numbers/>.
    
    For example, this field contains 6 for TCP,
    17 for UDP, 33 for DCCP, or 132 for SCTP.
    
    If this leaf is not instantiated, then the mapping
    applies to 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 also used to indicate the internal source ICMP
    identifier.
    
    As a reminder, all the ICMP Query messages contain
    an 'Identifier' field, which is referred to in this
    document as the 'ICMP Identifier'.";
            uses port-number;
          }  // container internal-src-port
    
          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
    interface of the NAT.
    
    It is also used to indicate the external source ICMP
    identifier.";
            uses port-number;
          }  // container external-src-port
    
          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 port numbers, 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 also used to include the internal
    destination ICMP identifier.";
            uses port-number;
          }  // container internal-dst-port
    
          leaf external-dst-address {
            type inet:ip-prefix;
            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 also used to include the external
    destination ICMP identifier.";
            uses port-number;
          }  // container external-dst-port
    
          leaf lifetime {
            type uint32;
            units "seconds";
            description
              "When specified, it is used to track the connection that is
    fully formed (e.g., once the three-way handshake
    TCP is completed) or the duration for maintaining
    an explicit mapping alive.  The mapping entry will be
    removed by the NAT instance once this lifetime is expired.
    
    When reported in a get operation, the lifetime indicates
    the remaining validity lifetime.
    
    Static mappings may not be associated with a
    lifetime.  If no lifetime is associated with a
    static mapping, an explicit action is required to
    remove that mapping.";
          }
        }  // grouping mapping-entry
    
        container nat {
          description "NAT module";
          container instances {
            description "NAT instances";
            list instance {
              key "id";
              description
                "A NAT instance.  This identifier can be automatically
    assigned or explicitly configured.";
              leaf id {
                type uint32;
                must ". >= 1";
                description
                  "NAT instance identifier.
    
    The identifier must be greater than zero.";
                reference
                  "RFC 7659: Definitions of Managed Objects for Network
                  	  Address Translators (NATs)";
    
              }
    
              leaf name {
                type string;
                description
                  "A name associated with the NAT instance.";
                reference
                  "RFC 7659: Definitions of Managed Objects for Network
                  	  Address Translators (NATs)";
    
              }
    
              leaf enable {
                type boolean;
                description
                  "Status of the NAT instance.";
              }
    
              container capabilities {
                config false;
                description "NAT capabilities.";
                leaf-list nat-flavor {
                  type identityref {
                    base nat-type;
                  }
                  description
                    "Supported translation type(s).";
                }
    
                leaf-list per-interface-binding {
                  type enumeration {
                    enum "unsupported" {
                      value 0;
                      description
                        "No capability to associate a NAT binding with
    an extra identifier.";
                    }
                    enum "layer-2" {
                      value 1;
                      description
                        "The NAT instance is able to associate a mapping with
    a Layer 2 identifier.";
                    }
                    enum "dslite" {
                      value 2;
                      description
                        "The NAT instance is able to associate a mapping with
    an IPv6 address (a.k.a., DS-Lite).";
                    }
                  }
                  description
                    "Indicates the capability of a NAT to associate a
    particular NAT session not only with the five
    tuples used for the transport connection on both
    sides of the NAT but also with the internal
    interface on which the user device is
    connected to the NAT.";
                  reference
                    "Section 4 of RFC 6619";
    
                }
    
                list transport-protocols {
                  key "protocol-id";
                  description
                    "List of supported protocols.";
                  leaf protocol-id {
                    type uint8;
                    mandatory true;
                    description
                      "The upper-layer protocol associated with a mapping.
    
    Values are taken from the IANA Protocol Numbers
    registry.
    
    For example, this field contains 6 for TCP,
    17 for UDP, 33 for DCCP, or 132 for SCTP.";
                  }
    
                  leaf protocol-name {
                    type string;
                    description
                      "The name of the upper-layer protocol associated
    with this mapping.
    
    For example, TCP, UDP, DCCP, and SCTP.";
                  }
                }  // list transport-protocols
    
                leaf restricted-port-support {
                  type boolean;
                  description
                    "Indicates source port NAT restriction support.";
                  reference
                    "RFC 7596: Lightweight 4over6: An Extension to
                    	  the Dual-Stack Lite Architecture";
    
                }
    
                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.";
                  reference
                    "Section 4.2.1 of RFC 4787";
    
                }
    
                leaf port-range-allocation-support {
                  type boolean;
                  description
                    "Indicates whether port range allocation is supported.";
                  reference
                    "Section 1.1 of RFC 7753";
    
                }
    
                leaf port-preservation-suport {
                  type boolean;
                  description
                    "Indicates whether port preservation is supported.";
                  reference
                    "Section 4.2.1 of RFC 4787";
    
                }
    
                leaf port-parity-preservation-support {
                  type boolean;
                  description
                    "Indicates whether port parity preservation is
    supported.";
                  reference
                    "Section 8 of RFC 7857";
    
                }
    
                leaf address-roundrobin-support {
                  type boolean;
                  description
                    "Indicates whether address allocation round robin is
    supported.";
                }
    
                leaf paired-address-pooling-support {
                  type boolean;
                  description
                    "Indicates whether paired-address-pooling is
    supported";
                  reference
                    "REQ-2 of RFC 4787";
    
                }
    
                leaf endpoint-independent-mapping-support {
                  type boolean;
                  description
                    "Indicates whether endpoint-independent-
    mapping is supported.";
                  reference
                    "Section 4 of RFC 4787";
    
                }
    
                leaf address-dependent-mapping-support {
                  type boolean;
                  description
                    "Indicates whether address-dependent-mapping is
    supported.";
                  reference
                    "Section 4 of RFC 4787";
    
                }
    
                leaf address-and-port-dependent-mapping-support {
                  type boolean;
                  description
                    "Indicates whether address-and-port-dependent-mapping is
    supported.";
                  reference
                    "Section 4 of RFC 4787";
    
                }
    
                leaf endpoint-independent-filtering-support {
                  type boolean;
                  description
                    "Indicates whether endpoint-independent-filtering is
    supported.";
                  reference
                    "Section 5 of RFC 4787";
    
                }
    
                leaf address-dependent-filtering {
                  type boolean;
                  description
                    "Indicates whether address-dependent-filtering is
    supported.";
                  reference
                    "Section 5 of RFC 4787";
    
                }
    
                leaf address-and-port-dependent-filtering {
                  type boolean;
                  description
                    "Indicates whether address-and-port-dependent is
    supported.";
                  reference
                    "Section 5 of RFC 4787";
    
                }
    
                leaf fragment-behavior {
                  type enumeration {
                    enum "unsupported" {
                      value 0;
                      description
                        "No capability to translate incoming fragments.
    All received fragments are dropped.";
                    }
                    enum "in-order" {
                      value 1;
                      description
                        "The NAT instance is able to translate fragments
    only if they are received in order.  That is, in
    particular the header is in the first packet.
    Fragments received out of order are dropped. ";
                    }
                    enum "out-of-order" {
                      value 2;
                      description
                        "The NAT instance is able to translate a fragment even
    if it is received out of order.
    
    This behavior is recommended.";
                      reference
                        "REQ-14 of RFC 4787";
    
                    }
                  }
                  description
                    "The fragment behavior is the NAT instance's capability to
    translate fragments received on the external interface of
    the NAT.";
                }
              }  // container capabilities
    
              leaf type {
                type identityref {
                  base nat-type;
                }
                description
                  "Specify the translation type.  Particularly useful when
    multiple translation flavors are supported.
    
    If one type is supported by a NAT, this parameter is by
    default set to that type.";
              }
    
              leaf per-interface-binding {
                type enumeration {
                  enum "disabled" {
                    value 0;
                    description
                      "Disable the capability to associate an extra identifier
    with NAT mappings.";
                  }
                  enum "layer-2" {
                    value 1;
                    description
                      "The NAT instance is able to associate a mapping with
    a Layer 2 identifier.";
                  }
                  enum "dslite" {
                    value 2;
                    description
                      "The NAT instance is able to associate a mapping with
    an IPv6 address (a.k.a., DS-Lite).";
                  }
                }
                description
                  "A NAT that associates a particular NAT session not
    only with the five tuples used for the transport
    connection on both sides of the NAT but also with
    the internal interface on which the user device is
    connected to the NAT.
    
    If supported, this mode of operation should be
    configurable, and it should be disabled by default in
    general-purpose NAT devices.
    If one single per-interface binding behavior is
    supported by a NAT, this parameter is by default set to
    that behavior.";
                reference
                  "Section 4 of RFC 6619";
    
              }
    
              list nat-pass-through {
                if-feature basic-nat44 or napt44 or dst-nat;
                key "id";
                description
                  "IP prefix NAT pass-through.";
                leaf id {
                  type uint32;
                  description
                    "An identifier of the IP prefix pass-through.";
                }
    
                leaf prefix {
                  type inet:ip-prefix;
                  mandatory true;
                  description
                    "The IP addresses that match should not be translated.
    
    It must be possible to administratively turn
    off translation for specific destination addresses
    and/or ports.";
                  reference
                    "REQ-6 of RFC 6888";
    
                }
    
                leaf port {
                  type inet:port-number;
                  description
                    "It must be possible to administratively turn off
    translation for specific destination addresses
    and/or ports.
    
    If no prefix is defined, the NAT pass-through bound
    to a given port applies for any destination address.";
                  reference
                    "REQ-6 of RFC 6888";
    
                }
              }  // list nat-pass-through
    
              list policy {
                key "id";
                description
                  "NAT parameters for a given instance";
                leaf id {
                  type uint32;
                  description
                    "An identifier of the NAT policy.  It must be unique
    within the NAT instance.";
                }
    
                container clat-parameters {
                  if-feature clat;
                  description "CLAT parameters.";
                  list clat-ipv6-prefixes {
                    key "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 translation since it requires
    NAT44 from the LAN to a single IPv4 address and then
    stateless translation to a single IPv6 address.";
                    reference
                      "RFC 6877: 464XLAT: Combination of Stateful and
                      	  Stateless Translation";
    
                    leaf ipv6-prefix {
                      type inet:ipv6-prefix;
                      description
                        "An IPv6 prefix used for CLAT.";
                    }
                  }  // list clat-ipv6-prefixes
    
                  list ipv4-prefixes {
                    key "ipv4-prefix";
                    description
                      "Pool of IPv4 addresses used for CLAT.
    192.0.0.0/29 is the IPv4 service continuity prefix.";
                    reference
                      "RFC 7335: IPv4 Service Continuity Prefix";
    
                    leaf 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
    translation 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: 464XLAT: Combination of Stateful and
                        	  Stateless Translation";
    
                    }
                  }  // list ipv4-prefixes
                }  // container clat-parameters
    
                list nptv6-prefixes {
                  if-feature nptv6;
                  key "internal-ipv6-prefix";
                  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 is an 'internal' network
    link attached to a leaf network within a single
    administrative domain, and the other is an
    'external' network with connectivity to the
    global Internet.";
                  reference
                    "RFC 6296: IPv6-to-IPv6 Network Prefix Translation";
    
                  leaf internal-ipv6-prefix {
                    type inet:ipv6-prefix;
                    mandatory true;
                    description
                      "An IPv6 prefix used by an internal interface of
    NPTv6.";
                    reference
                      "RFC 6296: IPv6-to-IPv6 Network Prefix Translation";
    
                  }
    
                  leaf external-ipv6-prefix {
                    type inet:ipv6-prefix;
                    mandatory true;
                    description
                      "An IPv6 prefix used by the external interface of
    NPTv6.";
                    reference
                      "RFC 6296: IPv6-to-IPv6 Network Prefix Translation";
    
                  }
                }  // list nptv6-prefixes
    
                list eam {
                  if-feature eam;
                  key "ipv4-prefix";
                  description
                    "The Explicit Address Mapping Table is 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 ipv4-prefix {
                    type inet:ipv4-prefix;
                    mandatory true;
                    description
                      "The IPv4 prefix of an EAM.";
                    reference
                      "Section 3.2 of RFC 7757";
    
                  }
    
                  leaf ipv6-prefix {
                    type inet:ipv6-prefix;
                    mandatory true;
                    description
                      "The IPv6 prefix of an EAM.";
                    reference
                      "Section 3.2 of RFC 7757";
    
                  }
                }  // list eam
    
                list nat64-prefixes {
                  if-feature siit or nat64 or clat;
                  key "nat64-prefix";
                  description
                    "Provides one or a list of NAT64 prefixes
    with or without a list of destination IPv4 prefixes.
    It allows mapping IPv4 address ranges to IPv6 prefixes.
    For example:
    192.0.2.0/24 is mapped to 2001:db8:122:300::/56.
    198.51.100.0/24 is mapped to 2001:db8:122::/48.";
                  reference
                    "Section 5.1 of RFC 7050";
    
                  leaf nat64-prefix {
                    type inet:ipv6-prefix;
                    mandatory true;
                    description
                      "A NAT64 prefix.  Can be a Network-Specific Prefix (NSP)
    or a Well-Known Prefix (WKP).
    
    Organizations deploying stateless IPv4/IPv6 translation
    should assign an NSP to their IPv4/IPv6 translation
    service.
    For stateless NAT64, IPv4-translatable IPv6 addresses
    must use the selected NSP.
    
    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.";
                    }
                  }  // list destination-ipv4-prefix
    
                  leaf stateless-enable {
                    type boolean;
                    default "false";
                    description
                      "Enable explicitly stateless NAT64.";
                  }
                }  // list nat64-prefixes
    
                list external-ip-address-pool {
                  if-feature basic-nat44 or napt44 or nat64;
                  key "pool-id";
                  description
                    "Pool of external IP addresses used to service internal
    hosts.
    
    A pool is a set of IP prefixes.";
                  leaf pool-id {
                    type uint32;
                    must ". >= 1";
                    description
                      "An identifier that uniquely identifies the address pool
    within a NAT instance.
    
    The identifier must be greater than zero.";
                    reference
                      "RFC 7659: Definitions of Managed Objects for
                      	  Network Address Translators (NATs)";
    
                  }
    
                  leaf external-ip-pool {
                    type inet:ipv4-prefix;
                    mandatory true;
                    description
                      "An IPv4 prefix used for NAT purposes.";
                  }
                }  // list external-ip-address-pool
    
                container port-set-restrict {
                  if-feature napt44 or nat64;
                  description
                    "Configures contiguous and non-contiguous port ranges.
    
    The port set is used to restrict the external source
    port numbers used by the translator.";
                  uses port-set;
                }  // container port-set-restrict
    
                leaf dst-nat-enable {
                  if-feature basic-nat44 or napt44;
                  type boolean;
                  default "false";
                  description
                    "Enable/disable Destination NAT.
    
    A NAT44 may be configured to enable Destination
    NAT, too.";
                }
    
                list dst-ip-address-pool {
                  if-feature dst-nat;
                  key "pool-id";
                  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
                      "Is used to identify an internal destination
    IP prefix/address to be translated.";
                  }
    
                  leaf dst-out-ip-pool {
                    type inet:ip-prefix;
                    mandatory true;
                    description
                      "IP address/prefix used for Destination NAT.";
                  }
                }  // list dst-ip-address-pool
    
                list transport-protocols {
                  if-feature napt44 or nat64 or dst-nat;
                  key "protocol-id";
                  description
                    "Configure the transport protocols to be handled by
    the translator.
    
    TCP and UDP are supported by default.";
                  leaf protocol-id {
                    type uint8;
                    mandatory true;
                    description
                      "The upper-layer protocol associated with this
    mapping.
    
    Values are taken from the IANA Protocol Numbers
    registry.
    
    For example, this field contains 6 for TCP,
    17 for UDP, 33 for DCCP, or 132 for SCTP.";
                  }
    
                  leaf protocol-name {
                    type string;
                    description
                      "The name of the upper-layer protocol associated
    with this mapping.
    
    For example, TCP, UDP, DCCP, and SCTP.";
                  }
                }  // list transport-protocols
    
                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 IPv6 address (internal side) to
    unambiguously identify a user device (e.g., 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-v6 (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 {
                  if-feature basic-nat44 or napt44 or dst-nat;
                  key "match-id";
                  description
                    "IP prefix match.
    A subscriber is identified by a subnet.";
                  leaf match-id {
                    type uint32;
                    description
                      "An identifier of the subscriber match.";
                  }
    
                  leaf subnet {
                    type inet:ip-prefix;
                    mandatory true;
                    description
                      "The IP address subnets that match
    should be translated.  For example, all addresses
    that belong to the 192.0.2.0/24 prefix must
    be processed by the NAT.";
                  }
                }  // list subscriber-match
    
                leaf address-allocation-type {
                  type enumeration {
                    enum "arbitrary" {
                      value 0;
                      description
                        "Arbitrary pooling behavior means that the NAT
    instance may create the new port mapping using any
    address in the pool that has a free port for the
    protocol concerned.";
                    }
                    enum "roundrobin" {
                      value 1;
                      description
                        "Round-robin allocation.";
                    }
                    enum "paired" {
                      value 2;
                      description
                        "Paired address pooling informs the NAT
    that all the flows from an internal IP
    address must be assigned the same external
    address.  This is the recommended behavior
    for NAPT/NAT64.";
                      reference
                        "RFC 4787: Network Address Translation (NAT)
                        	  Behavioral Requirements for Unicast UDP";
    
                    }
                  }
                  description
                    "Specifies how external IP addresses are allocated.";
                }
    
                leaf port-allocation-type {
                  if-feature napt44 or nat64;
                  type enumeration {
                    enum "random" {
                      value 0;
                      description
                        "Port randomization is enabled.  A NAT port allocation
    scheme should make it hard for attackers to guess
    port numbers";
                      reference
                        "REQ-15 of RFC 6888";
    
                    }
                    enum "port-preservation" {
                      value 1;
                      description
                        "Indicates whether the NAT should preserve the
    internal port number.";
                    }
                    enum
                      "port-parity-preservation" {
                      value 2;
                      description
                        "Indicates whether the NAT should preserve the port
    parity of the internal port number.";
                    }
                    enum "port-range-allocation" {
                      value 3;
                      description
                        "Indicates whether the NAT assigns a range of ports
    for an internal host.  This scheme allows the
    minimizing of the log volume.";
                      reference
                        "REQ-14 of RFC 6888";
    
                    }
                  }
                  description
                    "Indicates the type of port allocation.";
                }
    
                leaf mapping-type {
                  if-feature napt44 or nat64;
                  type enumeration {
                    enum "eim" {
                      value 0;
                      description
                        "endpoint-independent-mapping.";
                      reference
                        "Section 4 of RFC 4787";
    
                    }
                    enum "adm" {
                      value 1;
                      description
                        "address-dependent-mapping.";
                      reference
                        "Section 4 of RFC 4787";
    
                    }
                    enum "edm" {
                      value 2;
                      description
                        "address-and-port-dependent-mapping.";
                      reference
                        "Section 4 of RFC 4787";
    
                    }
                  }
                  description
                    "Indicates the type of NAT mapping.";
                }
    
                leaf filtering-type {
                  if-feature napt44 or nat64;
                  type enumeration {
                    enum "eif" {
                      value 0;
                      description
                        "endpoint-independent-filtering.";
                      reference
                        "Section 5 of RFC 4787";
    
                    }
                    enum "adf" {
                      value 1;
                      description
                        "address-dependent-filtering.";
                      reference
                        "Section 5 of RFC 4787";
    
                    }
                    enum "edf" {
                      value 2;
                      description
                        "address-and-port-dependent-filtering";
                      reference
                        "Section 5 of RFC 4787";
    
                    }
                  }
                  description
                    "Indicates the type of NAT filtering.";
                }
    
                leaf fragment-behavior {
                  if-feature napt44 or nat64;
                  type enumeration {
                    enum "drop-all" {
                      value 0;
                      description
                        "All received fragments are dropped.";
                    }
                    enum "in-order" {
                      value 1;
                      description
                        "Translate fragments only if they are received
    in order.";
                    }
                    enum "out-of-order" {
                      value 2;
                      description
                        "Translate a fragment even if it is received out
    of order.
    
    This behavior is recommended.";
                      reference
                        "REQ-14 of RFC 4787";
    
                    }
                  }
                  description
                    "The fragment behavior instructs the NAT about the
    behavior to follow to translate fragments received
    on the external interface of the NAT.";
                }
    
                list port-quota {
                  if-feature napt44 or nat64;
                  key "quota-type";
                  description
                    "Configures a port quota to be assigned per subscriber.
    It corresponds to the maximum 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 uint8;
                    description
                      "Indicates whether the port quota applies to
    all protocols (0) or to a specific protocol.";
                  }
                }  // list port-quota
    
                container port-set {
                  when
                    "../port-allocation-type = 'port-range-allocation'";
                  if-feature napt44 or nat64;
                  description
                    "Manages port-set assignments.";
                  leaf port-set-size {
                    type uint16;
                    mandatory true;
                    description
                      "Indicates the size of assigned port sets.";
                  }
    
                  leaf port-set-timeout {
                    type uint32;
                    units "seconds";
                    description
                      "inactivity timeout for port sets.";
                  }
                }  // container port-set
    
                container timers {
                  if-feature napt44 or nat64;
                  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: Network Address Translation (NAT)
                      	  Behavioral Requirements for Unicast UDP";
    
                  }
    
                  leaf tcp-idle-timeout {
                    type uint32;
                    units "seconds";
                    default "7440";
                    description
                      "TCP idle timeout should be 2 hours and 4 minutes.";
                    reference
                      "RFC 5382: NAT Behavioral Requirements for TCP";
    
                  }
    
                  leaf tcp-trans-open-timeout {
                    type uint32;
                    units "seconds";
                    default "240";
                    description
                      "The value of the transitory open connection
    idle-timeout.
    
    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.
    
    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";
                    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 NAT Behavioral Requirements for TCP";
    
                  }
    
                  leaf fragment-min-timeout {
                    when
                      "../../fragment-behavior='out-of-order'";
                    type uint32;
                    units "seconds";
                    default "2";
                    description
                      "As long as the NAT has available resources,
    the NAT allows the fragments to arrive
    over the fragment-min-timeout interval.
    The default value is inspired from RFC 6146.";
                  }
    
                  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: NAT Behavioral Requirements for ICMP";
    
                  }
    
                  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 123 (NTP), and longer timeouts
    on other ports.";
                    leaf port-number {
                      type inet:port-number;
                      description
                        "A port number.";
                    }
    
                    leaf protocol {
                      type uint8;
                      description
                        "The upper-layer protocol associated with this port.
    
    Values are taken from the IANA Protocol Numbers
    registry.
    
    If no protocol is indicated, it means 'any
    protocol'.";
                    }
    
                    leaf timeout {
                      type uint32;
                      units "seconds";
                      mandatory true;
                      description
                        "Timeout for this port number";
                    }
                  }  // list per-port-timeout
    
                  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 port pool.";
                    reference
                      "REQ-8 of RFC 6888";
    
                  }
                }  // container timers
    
                leaf fragments-limit {
                  when
                    "../fragment-behavior='out-of-order'";
                  type uint32;
                  description
                    "Limits the number of out-of-order fragments that can
    be handled.";
                  reference
                    "Section 11 of RFC 4787";
    
                }
    
                list algs {
                  key "name";
                  description
                    "Features related to the Application Layer
    Gateway (ALG).";
                  leaf name {
                    type string;
                    description
                      "The name of the ALG.";
                  }
    
                  leaf transport-protocol {
                    type uint32;
                    description
                      "The transport protocol used by the ALG
    (e.g., TCP and UDP).";
                  }
    
                  container dst-transport-port {
                    description
                      "The destination port number(s) used by the ALG.
    For example,
      - 21 for the FTP ALG
      - 53 for the DNS ALG.";
                    uses port-number;
                  }  // container dst-transport-port
    
                  container src-transport-port {
                    description
                      "The source port number(s) used by the ALG.";
                    uses port-number;
                  }  // container src-transport-port
    
                  leaf status {
                    type boolean;
                    description
                      "Enable/disable the ALG.";
                  }
                }  // list algs
    
                leaf all-algs-enable {
                  type boolean;
                  description
                    "Disable/enable all ALGs.
    
    When specified, this parameter overrides the one
    that may be indicated, eventually, by the 'status'
    of an individual ALG.";
                }
    
                container notify-pool-usage {
                  if-feature basic-nat44 or napt44 or nat64;
                  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 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 10.
    
    0% indicates that low-threshold notification is
    disabled.";
                  }
    
                  leaf high-threshold {
                    type percent;
                    must ". >= ../low-threshold" {
                      error-message
                        "The high threshold must be greater than or equal
    to the low threshold.";
                    }
                    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.
    
    Setting the same value as low-threshold is equivalent
    to disabling high-threshold notification.";
                  }
    
                  leaf notify-interval {
                    type uint32 {
                      range "1 .. 3600";
                    }
                    units "seconds";
                    default "20";
                    description
                      "Minimum number of seconds between successive
    notifications for this pool.";
                    reference
                      "RFC 7659: Definitions of Managed Objects for
                      	  Network Address Translators (NATs)";
    
                  }
                }  // container notify-pool-usage
    
                container external-realm {
                  description
                    "Identifies the external realm of the NAT instance.";
                  choice realm-type {
                    description
                      "Can be an interface, VRF instance, etc.";
                    case interface {
                      description
                        "External interface.";
                      leaf external-interface {
                        type if:interface-ref;
                        description
                          "Name of the external interface.";
                      }
                    }  // case interface
                  }  // choice realm-type
                }  // container external-realm
              }  // list policy
    
              container mapping-limits {
                if-feature napt44 or nat64;
                description
                  "Information about the configuration parameters that
    limits the mappings based upon various criteria.";
                leaf limit-subscribers {
                  type uint32;
                  description
                    "Maximum number of subscribers that can be serviced
    by a NAT instance.
    
    A subscriber is identified by a given prefix.";
                  reference
                    "RFC 7659: Definitions of Managed Objects for
                    	  Network Address Translators (NATs)";
    
                }
    
                leaf limit-address-mappings {
                  type uint32;
                  description
                    "Maximum number of address mappings that can be
    handled by a NAT instance.
    
    When this limit is reached, packets that would
    normally trigger translation will be dropped.";
                  reference
                    "RFC 7659: Definitions of Managed Objects for
                    	  Network Address Translators (NATs)";
    
                }
    
                leaf limit-port-mappings {
                  type uint32;
                  description
                    "Maximum number of port mappings that can be handled
    by a NAT instance.
    
    When this limit is reached, packets that would
    normally trigger translation will be dropped.";
                  reference
                    "RFC 7659: Definitions of Managed Objects for
                    	  Network Address Translators (NATs)";
    
                }
    
                list limit-per-protocol {
                  if-feature napt44 or nat64 or dst-nat;
                  key "protocol-id";
                  description
                    "Configure limits per transport protocol";
                  leaf protocol-id {
                    type uint8;
                    mandatory true;
                    description
                      "The upper-layer protocol.
    
    Values are taken from the IANA Protocol Numbers
    registry.
    
    For example, this field contains 6 for TCP,
    17 for UDP, 33 for DCCP, or 132 for SCTP.";
                  }
    
                  leaf limit {
                    type uint32;
                    description
                      "Maximum number of protocol-specific NAT mappings
    per instance.";
                  }
                }  // list limit-per-protocol
              }  // container mapping-limits
    
              container connection-limits {
                if-feature basic-nat44 or napt44 or nat64;
                description
                  "Information about the configuration parameters that
    rate-limit the translation based upon various criteria.";
                leaf limit-per-subscriber {
                  type uint32;
                  units "bits/second";
                  description
                    "Rate-limit the number of new mappings and sessions
    per subscriber.";
                }
    
                leaf limit-per-instance {
                  type uint32;
                  units "bits/second";
                  description
                    "Rate-limit the number of new mappings and sessions
    per instance.";
                }
    
                list limit-per-protocol {
                  if-feature napt44 or nat64;
                  key "protocol-id";
                  description
                    "Configure limits per transport protocol";
                  leaf protocol-id {
                    type uint8;
                    mandatory true;
                    description
                      "The upper-layer protocol.
    
    Values are taken from the IANA Protocol Numbers
    registry.
    
    For example, this field contains 6 for TCP,
    17 for UDP, 33 for DCCP, or 132 for SCTP.";
                  }
    
                  leaf limit {
                    type uint32;
                    description
                      "Limit the number of protocol-specific mappings
    and sessions per instance.";
                  }
                }  // list limit-per-protocol
              }  // container connection-limits
    
              container notification-limits {
                description
                  "Sets notification limits.";
                leaf notify-interval {
                  if-feature basic-nat44 or napt44 or nat64;
                  type uint32 {
                    range "1 .. 3600";
                  }
                  units "seconds";
                  default "10";
                  description
                    "Minimum number of seconds between successive
    notifications for this NAT instance.";
                  reference
                    "RFC 7659: Definitions of Managed Objects for
                    	  Network Address Translators (NATs)";
    
                }
    
                leaf notify-addresses-usage {
                  if-feature basic-nat44 or napt44 or nat64;
                  type percent;
                  description
                    "Notification of address mappings usage over
    the whole NAT instance.
    
    Notification must be generated when the defined
    threshold is reached.
    
    For example, if a notification is required when
    the address mappings utilization reaches 90%,
    this configuration parameter must be set
    to 90.";
                }
    
                leaf notify-ports-usage {
                  if-feature napt44 or nat64;
                  type percent;
                  description
                    "Notification of port mappings usage over the
    whole NAT instance.
    
    Notification must be generated when the defined
    threshold is reached.
    
    For example, if a notification is required when
    the port mappings utilization reaches 90%, this
    configuration parameter must be set to 90.";
                }
    
                leaf notify-subscribers-limit {
                  if-feature basic-nat44 or napt44 or nat64;
                  type uint32;
                  description
                    "Notification of active subscribers per NAT
    instance.
    
    Notification must be generated when the defined
    threshold is reached.";
                }
              }  // container notification-limits
    
              container mapping-table {
                if-feature basic-nat44 or napt44 or nat64 or clat or dst-nat;
                description
                  "NAT mapping table.  Applicable for functions that maintain
    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;
                }  // list mapping-entry
              }  // container mapping-table
    
              container statistics {
                config false;
                description
                  "Statistics related to the NAT instance.";
                leaf discontinuity-time {
                  type yang:date-and-time;
                  mandatory true;
                  description
                    "The time on the most recent occasion at which the NAT
    instance suffered a discontinuity.  This must be
    initialized when the NAT instance is configured
    or rebooted.";
                }
    
                container traffic-statistics {
                  description
                    "Generic traffic statistics.";
                  leaf sent-packets {
                    type yang:zero-based-counter64;
                    description
                      "Number of packets sent.";
                  }
    
                  leaf sent-bytes {
                    type yang:zero-based-counter64;
                    units "bytes";
                    description
                      "Counter for sent traffic in bytes.";
                  }
    
                  leaf rcvd-packets {
                    type yang:zero-based-counter64;
                    description
                      "Number of received packets.";
                  }
    
                  leaf rcvd-bytes {
                    type yang:zero-based-counter64;
                    units "bytes";
                    description
                      "Counter for received traffic in bytes.";
                  }
    
                  leaf dropped-packets {
                    type yang:zero-based-counter64;
                    description
                      "Number of dropped packets.";
                  }
    
                  leaf dropped-bytes {
                    type yang:zero-based-counter64;
                    units "bytes";
                    description
                      "Counter for dropped traffic in bytes.";
                  }
    
                  leaf dropped-fragments {
                    if-feature napt44 or nat64;
                    type yang:zero-based-counter64;
                    description
                      "Number of dropped fragments on the external realm.";
                  }
    
                  leaf dropped-address-limit-packets {
                    if-feature basic-nat44 or napt44 or nat64;
                    type yang:zero-based-counter64;
                    description
                      "Number of dropped packets because an address limit
     is reached.";
                  }
    
                  leaf dropped-address-limit-bytes {
                    if-feature basic-nat44 or napt44 or nat64;
                    type yang:zero-based-counter64;
                    units "bytes";
                    description
                      "Counter of dropped packets because an address limit
     is reached, in bytes.";
                  }
    
                  leaf dropped-address-packets {
                    if-feature basic-nat44 or napt44 or nat64;
                    type yang:zero-based-counter64;
                    description
                      "Number of dropped packets because no address is
    available for allocation.";
                  }
    
                  leaf dropped-address-bytes {
                    if-feature basic-nat44 or napt44 or nat64;
                    type yang:zero-based-counter64;
                    units "bytes";
                    description
                      "Counter of dropped packets because no address is
    available for allocation, in bytes.";
                  }
    
                  leaf dropped-port-limit-packets {
                    if-feature napt44 or nat64;
                    type yang:zero-based-counter64;
                    description
                      "Number of dropped packets because a port limit
    is reached.";
                  }
    
                  leaf dropped-port-limit-bytes {
                    if-feature napt44 or nat64;
                    type yang:zero-based-counter64;
                    units "bytes";
                    description
                      "Counter of dropped packets because a port limit
    is reached, in bytes.";
                  }
    
                  leaf dropped-port-packets {
                    if-feature napt44 or nat64;
                    type yang:zero-based-counter64;
                    description
                      "Number of dropped packets because no port is
    available for allocation.";
                  }
    
                  leaf dropped-port-bytes {
                    if-feature napt44 or nat64;
                    type yang:zero-based-counter64;
                    units "bytes";
                    description
                      "Counter of dropped packets because no port is
    available for allocation, in bytes.";
                  }
    
                  leaf dropped-subscriber-limit-packets {
                    if-feature basic-nat44 or napt44 or nat64;
                    type yang:zero-based-counter64;
                    description
                      "Number of dropped packets because the subscriber
    limit per instance is reached.";
                  }
    
                  leaf dropped-subscriber-limit-bytes {
                    if-feature basic-nat44 or napt44 or nat64;
                    type yang:zero-based-counter64;
                    units "bytes";
                    description
                      "Counter of dropped packets because the subscriber
     limit per instance is reached, in bytes.";
                  }
                }  // container traffic-statistics
    
                container mappings-statistics {
                  description
                    "Mappings statistics.";
                  leaf total-active-subscribers {
                    if-feature basic-nat44 or napt44 or nat64;
                    type yang:gauge32;
                    description
                      "Total number of active subscribers (that is,
    subscribers for which the NAT maintains active
    mappings).
    
    A subscriber is identified by a subnet,
    subscriber-mask, etc.";
                  }
    
                  leaf total-address-mappings {
                    if-feature basic-nat44 or napt44 or nat64 or clat or dst-nat;
                    type yang:gauge32;
                    description
                      "Total number of address mappings present at a given
    time.  It includes both static and dynamic mappings.";
                    reference
                      "Section 3.3.8 of RFC 7659";
    
                  }
    
                  leaf total-port-mappings {
                    if-feature napt44 or nat64;
                    type yang:gauge32;
                    description
                      "Total number of NAT port mappings present at
    a given time.  It includes both static and dynamic
    mappings.";
                    reference
                      "Section 3.3.9 of RFC 7659";
    
                  }
    
                  list total-per-protocol {
                    if-feature napt44 or nat64;
                    key "protocol-id";
                    description
                      "Total mappings for each enabled/supported protocol.";
                    leaf protocol-id {
                      type uint8;
                      mandatory true;
                      description
                        "The upper-layer protocol.
    For example, this field contains 6 for TCP,
    17 for UDP, 33 for DCCP, or 132 for SCTP.";
                    }
    
                    leaf total {
                      type yang:gauge32;
                      description
                        "Total number of a protocol-specific mappings present
    at a given time.  The protocol is identified by
    protocol-id.";
                    }
                  }  // list total-per-protocol
                }  // container mappings-statistics
    
                container pools-stats {
                  if-feature basic-nat44 or napt44 or nat64;
                  description
                    "Statistics related to address/prefix pools
    usage";
                  leaf addresses-allocated {
                    type yang:gauge32;
                    description
                      "Number of all allocated addresses.";
                  }
    
                  leaf addresses-free {
                    type yang:gauge32;
                    description
                      "Number of unallocated addresses of all pools at
    a given time.  The sum of unallocated and allocated
    addresses is the total number of addresses of
    the pools.";
                  }
    
                  container ports-stats {
                    if-feature napt44 or nat64;
                    description
                      "Statistics related to port numbers usage.";
                    leaf ports-allocated {
                      type yang:gauge32;
                      description
                        "Number of allocated ports from all pools.";
                    }
    
                    leaf ports-free {
                      type yang:gauge32;
                      description
                        "Number of unallocated addresses from all pools.";
                    }
                  }  // container ports-stats
    
                  list per-pool-stats {
                    if-feature basic-nat44 or napt44 or nat64;
                    key "pool-id";
                    description
                      "Statistics related to address/prefix pool usage";
                    leaf pool-id {
                      type uint32;
                      description
                        "Unique identifier that represents a pool of
    addresses/prefixes.";
                    }
    
                    leaf discontinuity-time {
                      type yang:date-and-time;
                      mandatory true;
                      description
                        "The time on the most recent occasion at which this
    pool counter suffered a discontinuity.  This must
    be initialized when the address pool is
    configured.";
                    }
    
                    container pool-stats {
                      description
                        "Statistics related to address/prefix pool usage";
                      leaf addresses-allocated {
                        type yang:gauge32;
                        description
                          "Number of allocated addresses from this pool.";
                      }
    
                      leaf addresses-free {
                        type yang:gauge32;
                        description
                          "Number of unallocated addresses in this pool.";
                      }
                    }  // container pool-stats
    
                    container port-stats {
                      if-feature napt44 or nat64;
                      description
                        "Statistics related to port numbers usage.";
                      leaf ports-allocated {
                        type yang:gauge32;
                        description
                          "Number of allocated ports from this pool.";
                      }
    
                      leaf ports-free {
                        type yang:gauge32;
                        description
                          "Number of unallocated addresses from this pool.";
                      }
                    }  // container port-stats
                  }  // list per-pool-stats
                }  // container pools-stats
              }  // container statistics
            }  // list instance
          }  // container instances
        }  // container nat
    
        notification nat-pool-event {
          if-feature basic-nat44 or napt44 or nat64;
          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 {
            type leafref {
              path "/nat/instances/instance/id";
            }
            mandatory true;
            description
              "NAT instance identifier.";
          }
    
          leaf policy-id {
            type leafref {
              path "/nat/instances/instance/policy/id";
            }
            description "Policy identifier.";
          }
    
          leaf pool-id {
            type leafref {
              path "/nat/instances/instance/policy/external-ip-address-pool/pool-id";
            }
            mandatory true;
            description "Pool Identifier.";
          }
    
          leaf notify-pool-threshold {
            type percent;
            mandatory true;
            description
              "A threshold (high threshold or low threshold) has
    been fired.";
          }
        }  // notification nat-pool-event
    
        notification nat-instance-event {
          if-feature basic-nat44 or napt44 or nat64;
          description
            "Notifications must be generated when notify-addresses-usage
    and/or notify-ports-usage thresholds are reached.";
          leaf id {
            type leafref {
              path "/nat/instances/instance/id";
            }
            mandatory true;
            description
              "NAT instance identifier.";
          }
    
          leaf notify-subscribers-threshold {
            type uint32;
            description
              "The notify-subscribers-limit threshold has been fired.";
          }
    
          leaf notify-addresses-threshold {
            type percent;
            description
              "The notify-addresses-usage threshold has been fired.";
          }
    
          leaf notify-ports-threshold {
            type percent;
            description
              "The notify-ports-usage threshold has been fired.";
          }
        }  // notification nat-instance-event
      }  // module ietf-nat
    

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