Questions tagged [ietf-netmod-yang]

YANG is the data modeling language for the Network Configuration Protocol (NETCONF). The name is an acronym for Yet Another Next Generation. The YANG data modeling language was developed by the NETMOD working group (NETMOD WG) in the Internet Engineering Task Force (IETF) and was published as RFC 6020 in October 2010. A new maintenance release of the core YANG specification has been published by the NETMOD WG in August 2016 (YANG 1.1, RFC 7950).

YANG is a language originally designed to model data for the NETCONF protocol. A YANG module defines a hierarchy of data that can be used for NETCONF-based operations, including configuration, state data, Remote Procedure Calls (RPCs), and notifications. This allows a complete description of all data sent between a NETCONF client and server. Although out of scope for YANG specification, YANG can also be used with protocols other than NETCONF.

YANG models the hierarchical organization of data as a tree in which each node has a name, and either a value or a set of child nodes. It provides clear and concise descriptions of the nodes, as well as the interaction between those nodes.

An example YANG module:

module example-forest {

  namespace "http://example.org/example-forest";
  prefix et;
  revision 2015-11-26;

  import ietf-yang-types {
    prefix yang;
  }

  typedef tree-species {
    type string;
    description "Defines the species of a tree.";
  }

  typedef a-tree {
    type leafref {
      path "/et:forest/et:trees/et:tree/et:id";
    }
    description "Represents a known tree.";
  }

  /*
   * Our forest.
   */
  container forest {
    description "A forest full of trees and potentially other stuff.";

    container trees {
      description "The trees of a forest.";

      list tree {
        description "Describes one tree in a forest.";        
        key id;

        leaf id {
          type string;
          description "A unique identifier of a tree.";
        }
        leaf species {
          type et:tree-species;
          description "The tree species.";
          mandatory true;
        }        
        leaf description {
          type string;
          description "A short description of the tree.";
        }
        leaf location {
          type string;
          mandatory true;
          description "The location of the tree";
        }
        leaf height {
          type uint8;
          units "meters";
          description "The height of the tree.";
        }

      }
    }
  }

  /**
   * Cutting schedules.
   */
  container cutting-schedules {
    description "Our cutting schedules.";

    list cutting-schedule {
      description "A cutting schedule.";    
      key "name date";

      leaf name {
        type string;
        description "A name for the schedule.";
      }
      leaf date {
        type yang:date-and-time;
        description "When to start cutting down trees.";
      }
      leaf-list tree {
        type a-tree;
        min-elements 1;
        description "Which trees to cut down.";
      }
    }
  }
}

Sample data in XML encoding:

<?xml version="1.0" encoding="utf-8"?>
<data xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">

  <forest xmlns="http://example.org/example-forest">
    <trees>
      <tree>
        <id>Lisa</id>
        <species>pine</species>
        <location>Right in the centre of the forest.</location>
        <height>15</height>
      </tree>
      <tree>
        <id>Bob</id>
        <species>oak</species>
        <location>At the first Y split of the path through forest.</location>
        <height>20</height>
      </tree>
      <tree>
        <id>John</id>
        <species>birch</species>
        <description>Struck by lightning a few years ago.</description>
        <location>Next to the burnt down tree-house debris.</location>
        <height>10</height>
      </tree>
    </trees>
  </forest>

  <cutting-schedules xmlns="http://example.org/example-forest">
    <cutting-schedule>
      <name>High priority cleanup</name>
      <date>2015-11-30T16:00:00Z</date>
      <tree>Bob</tree>
      <tree>John</tree>
    </cutting-schedule>
  </cutting-schedules>

</data>

Learn more about YANG here:

• wikipedia page,
• YANG by Example video tutorial,
• the specification, version 1 (RFC 6020),
• the specification, version 1.1 (RFC 7950).