module ietf-isis-reverse-metric {

    yang-version 1.1;

    namespace
      "urn:ietf:params:xml:ns:yang:ietf-isis-reverse-metric";

    prefix isis-rmetric;

    import ietf-routing {
      prefix rt;
      reference
        "RFC 8349: A YANG Data Model for Routing Management
        	  (NMDA Version)";


    }
    import ietf-isis {
      prefix isis;
      reference
        "RFC 9130: YANG Data Model for the IS-IS Protocol";


    }

    organization
      "IETF LSR Working Group (LSR)";

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

     Author:  Christian Hopps
              <mailto:chopps@chopps.org>";

    description
      "This module defines the configuration and operational state
     for managing the IS-IS reverse metric functionality
     (RFC 8500).

     Copyright (c) 2022 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 Revised BSD License set
     forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC 9194; see the
     RFC itself for full legal notices.";

    reference
      "RFC 8500: IS-IS Routing with Reverse Metric";


    revision "2022-10-19" {
      description "Initial revision.";
      reference
        "RFC 9194: A YANG Module for IS-IS Reverse Metric";

    }


    grouping reverse-metric-data {
      description
        "IS-IS reverse metric data.";
      leaf metric {
        type isis:wide-metric;
        description
          "The reverse metric value.";
        reference
          "RFC 8500: IS-IS Routing with Reverse Metric, Section 2";

      }

      container flags {
        description
          "The reverse metric flag values.";
        leaf whole-lan {
          type boolean;
          description
            "The 'Whole LAN' bit (W bit) (RFC 8500).  If true, then
           a Designated Intermediate System (DIS) processing this
           reverse metric will add the metric value to all the
           nodes it advertises in the pseudonode Link State
           Protocol Data Unit (LSP) for this interface.
           Otherwise, it will only increment the metric for the
           advertising node in the pseudonode LSP for this
           interface.";
          reference
            "RFC 8500: IS-IS Routing with Reverse Metric,
            	  Section 2";

        }

        leaf allow-unreachable {
          type boolean;
          description
            "The 'Unreachable' bit (U bit) (RFC 8500).  If true, it
           allows the neighbor to increment the overall metric up
           to 2^24-1 rather than the lesser maximum of 2^24-2.
           If the metric is then set by the neighbor to 2^24-1,
           it will cause traffic to stop using, rather than avoid
           using, the interface.";
          reference
            "RFC 8500: IS-IS Routing with Reverse Metric,
            	  Section 2";

        }
      }  // container flags
    }  // grouping reverse-metric-data

    grouping reverse-metric-if-config-data {
      description
        "IS-IS reverse metric config data.";
      uses reverse-metric-data;

      leaf exclude-te-metric {
        type boolean;
        default "false";
        description
          "If true and there is a TE metric defined for this
         interface, then do not send the Traffic Engineering
         Metric sub-TLV in the Reverse Metric TLV.";
        reference
          "RFC 8500: IS-IS Routing with Reverse Metric, Section 2";

      }
    }  // grouping reverse-metric-if-config-data

    grouping tlv16-reverse-metric {
      description
        "IS-IS Reverse Metric TLV data.";
      uses reverse-metric-data;

      leaf te-metric {
        type uint32;
        description
          "The TE metric value from the sub-TLV, if present.";
        reference
          "RFC 8500: IS-IS Routing with Reverse Metric, Section 2";

      }
    }  // grouping tlv16-reverse-metric

    augment /rt:routing/rt:control-plane-protocols/rt:control-plane-protocol/isis:isis {
      when
        "derived-from-or-self(../rt:type, 'isis:isis')" {
        description
          "This augment is only valid when the routing protocol
         instance type is 'isis'.";
      }
      description
        "The reverse metric configuration for an IS-IS instance.";
      container reverse-metric {
        description
          "Global reverse metric configuration.";
        leaf enable-receive {
          type boolean;
          default "false";
          description
            "Enables handling of reverse metric announcements from
           neighbors.  By default, reverse metric handling is
           disabled and must be explicitly enabled through this
           configuration.";
        }
      }  // container reverse-metric
    }

    augment /rt:routing/rt:control-plane-protocols/rt:control-plane-protocol/isis:isis/isis:interfaces/isis:interface {
      when
        "derived-from-or-self(../../../rt:type, 'isis:isis')" {
        description
          "This augment is only valid when the routing protocol
         instance type is 'isis'.";
      }
      description
        "The reverse metric configuration for an interface.";
      container reverse-metric {
        description
          "Announces a reverse metric to neighbors.  The
         configuration is hierarchical and follows the same
         behavior as that defined for per-level values in the
         augmented base module.

         Reverse metric operation is enabled by the configuration
         of a 'reverse-metric' metric value either at the top
         level or under a level-specific container node.  If a
         'reverse-metric' metric value is only specified under a
         level-specific container node, then operation is only
         enabled at the specified level.

         As the reverse metric is advertised in IS-IS Hello
         Protocol Data Units (IIH PDUs), level-specific
         configuration is only available for broadcast interface
         types.";
        uses reverse-metric-if-config-data {
          refine flags/whole-lan {
            default "false";
          }

          refine flags/allow-unreachable {
            default "false";
          }
        }

        container level-1 {
          when
            '../../isis:interface-type = "broadcast"';
          description
            "Announces a reverse metric to level-1 neighbors.";
          uses reverse-metric-if-config-data;
        }  // container level-1

        container level-2 {
          when
            '../../isis:interface-type = "broadcast"';
          description
            "Announces a reverse metric to level-2 neighbors.";
          uses reverse-metric-if-config-data;
        }  // container level-2
      }  // container reverse-metric
    }

    augment /rt:routing/rt:control-plane-protocols/rt:control-plane-protocol/isis:isis/isis:interfaces/isis:interface/isis:adjacencies/isis:adjacency {
      when
        "derived-from-or-self(../../../../../rt:type,
                               'isis:isis')" {
        description
          "This augment is only valid when the routing protocol
         instance type is 'isis'.";
      }
      description
        "The reverse metric state advertised by an adjacency.";
      container reverse-metric {
        description
          "IS-IS Reverse Metric TLV data.";
        uses tlv16-reverse-metric;
      }  // container reverse-metric
    }
  }  // module ietf-isis-reverse-metric