module ietf-network {
     yang-version 1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-network";
     prefix nd;

     organization
       "IETF I2RS (Interface to the Routing System) Working Group";     
    grouping node-ref {
       description
         "Contains the information necessary to reference a node.";
       container node-from-grouping {
             leaf node-ref {
                type leafref {
                 path "/networks/network/node/node-id";
                   require-instance false;
                  }
              }
         }
     }
     container networks {
       description
         "Serves as top-level container for a list of networks.";
       list network {
         key "network-id";
         description
           "Describes a network.
            A network typically contains an inventory of nodes,
            topological information (augmented through
            network-topology model), as well as layering
            information.";
         container network-types {
           description
             "Serves as an augmentation target.
              The network type is indicated through corresponding
              presence containers augmented into this container.";
         }
         leaf network-id {
           type string;
           description
             "Identifies a network.";
         }
         list supporting-network {
           key "network-ref";
           description
             "An underlay network, used to represent layered network
              topologies.";
           leaf network-ref {
             type leafref {
               path "/networks/network/network-id";
             require-instance false;
             }
             description
               "References the underlay network.";
           }
         }
         list node {
           key "node-id";
           description
             "The inventory of nodes of this network.";
           leaf node-id {
             type uint8;
             description
               "Identifies a node uniquely within the containing
                network.";
           }
           list supporting-node {
             key "network-ref node-ref";
             description
               "Represents another node, in an underlay network, that
                this node is supported by.  Used to represent layering
                structure.";
             leaf network-ref {
               type leafref {
                 path "../../../supporting-network/network-ref";
               require-instance false;
               }
               description
                 "References the underlay network that the
                  underlay node is part of.";
             }
             leaf node-ref {
               type leafref {
                 path "/networks/network/node/node-id";
               require-instance false;
               }
               description
                 "References the underlay node itself.";
             }
           }
         }
       }
       uses node-ref;
     }

}