module ietf-dslite {

    yang-version 1.1;

    namespace
      "urn:ietf:params:xml:ns:yang:ietf-dslite";

    prefix dslite;

    import ietf-inet-types {
      prefix inet;
      reference
        "Section 4 of RFC 6991";


    }
    import ietf-interfaces {
      prefix if;
      reference
        "RFC 8343: A YANG Data Model for Interface Management";


    }
    import iana-if-type {
      prefix ianaift;
      reference
        "RFC 7224: IANA Interface Type YANG Module";


    }
    import ietf-nat {
      prefix nat;
      reference
        "RFC 8512: A YANG Module for Network Address Translation (NAT)
        	  and Network Prefix Translation (NPT)";


    }
    import ietf-yang-types {
      prefix yang;
      reference
        "Section 3 of RFC 6991";


    }

    organization
      "IETF Softwire Working Group";

    contact
      "WG Web:   <https://datatracker.ietf.org/wg/softwire/>
    WG List:  <mailto:softwires@ietf.org>

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

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

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

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

    Copyright (c) 2018 IETF Trust and the persons identified as
    authors of the code.  All rights reserved.

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

    This version of this YANG module is part of RFC 8513; see
    the RFC itself for full legal notices.";

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

    }


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

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

    }

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

    }

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

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

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

      }

      leaf ipv4-address {
        type inet:ipv4-address;
        description
          "IPv4 address of the local DS-Lite AFTR or B4.

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

        This address can be used to report ICMP problems and will
        appear in traceroute outputs.";
        reference
          "RFC 6333: Dual-Stack Lite Broadband Deployments Following
          	  IPv4 Exhaustion";

      }

      leaf aftr-ipv6-addr {
        if-feature b4;
        type inet:ipv6-address;
        description
          "Indicates the AFTR's IPv6 address to be used by a B4
        element.";
        reference
          "RFC 6333: Dual-Stack Lite Broadband Deployments Following
          	  IPv4 Exhaustion";

      }

      leaf tunnel-mtu {
        type uint16;
        description
          "Configures a tunnel MTU.

        RFC 6908 specifies that since fragmentation and reassembly
        are not optimal, the operator should do everything possible
        to eliminate the need for them.  If the operator uses simple
        IPv4-in-IPv6 softwire, it is recommended that the MTU size
        of the IPv6 network between the B4 and the AFTR account
        for the additional overhead (40 bytes).";
        reference
          "RFC 6908: Deployment Considerations for Dual-Stack Lite";

      }

      leaf v6-v4-dscp-preservation {
        type boolean;
        description
          "Copies the DSCP value from the IPv6 header, and vice versa.

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

      }
    }

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

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

        This policy aims to prevent a misbehaving subscriber from
        mounting several DS-Lite softwires that would consume
        additional AFTR resources (e.g., get more external ports
        if the quota was enforced on a per-softwire basis and
        consume extra processing due to a large number of active
        softwires).";
        reference
          "Section 4 of RFC 7785";

      }

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

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

        The AFTR uses the subscriber-mask-v6 to determine whether two
        IPv6 addresses belong to the same CPE (e.g., if the
        subscriber-mask-v6 is set to 56, the AFTR concludes that
        2001:db8:100:100::1 and 2001:db8:100:100::2 belong to the same
        CPE assigned with 2001:db8:100:100::/56).";
        reference
          "RFC 7785: Recommendations for Prefix Binding in the Context
          	  of Softwire Dual-Stack Lite";

      }

      leaf b4-address-change-limit {
        type uint32;
        units "seconds";
        default "1800";
        description
          "Minimum number of seconds between a successive B4's IPv6
        address change from the same prefix.

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

        It is recommended that this rate limit be set to 30 minutes;
        other values can be set on a per-deployment basis.";
        reference
          "RFC 7785: Recommendations for Prefix Binding in the Context
          	  of Softwire Dual-Stack Lite";

      }

      container mss-clamping {
        description
          "MSS rewriting configuration to avoid IPv6 fragmentation.";
        leaf enable {
          type boolean;
          description
            "Enable/disable MSS rewriting feature.";
        }

        leaf mss-value {
          type uint16;
          units "octets";
          description
            "Sets the MSS value to be used for MSS rewriting.";
        }
      }  // container mss-clamping
    }

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

        }

        leaf last-address-change {
          type yang:date-and-time;
          description
            "Records the last time that the address changed.";
        }
      }  // container b4-ipv6-address

      leaf v6-dscp {
        when
          "/if:interfaces/if:interface"
            + "/dslite:v6-v4-dscp-preservation = 'true'";
        type inet:dscp;
        description
          "DSCP value used at the softwire level (i.e., IPv6 header).";
      }

      leaf internal-v4-dscp {
        when
          "/if:interfaces/if:interface"
            + "/dslite:v6-v4-dscp-preservation = 'true'";
        type inet:dscp;
        description
          "DSCP value of the encapsulated IPv4 packet.";
      }

      leaf external-v4-dscp {
        when
          "/if:interfaces/if:interface"
            + "/dslite:v6-v4-dscp-preservation = 'true'";
        type inet:dscp;
        description
          "DSCP value of the translated IPv4 packet as marked by
        the AFTR.";
      }
    }

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

    notification b4-address-change-limit-policy-violation {
      if-feature aftr;
      description
        "Generates notifications when a B4 unsuccessfully attempts
      to change the IPv6 address in a time shorter than the value
      of b4-address-change-limit.
      Notifications are rate-limited (notify-interval).";
      leaf id {
        type leafref {
          path "/nat:nat/nat:instances/nat:instance/nat:id";
        }
        mandatory true;
        description
          "NAT instance identifier.";
      }

      leaf policy-id {
        type leafref {
          path "/nat:nat/nat:instances/nat:instance/nat:policy/nat:id";
        }
        mandatory true;
        description "Policy identifier.";
      }

      leaf address {
        type inet:ipv6-address;
        mandatory true;
        description "B4's IPv6 address.";
      }
    }  // notification b4-address-change-limit-policy-violation
  }  // module ietf-dslite