code: def add_cluster_virtual_interface(self, interface_id, cluster_virtual=None,
                      network_value=None, nodes=None, zone_ref=None, comment=None):
          
          interfaces = [{'cluster_virtual': cluster_virtual, 'network_value': network_value,
                         'nodes': nodes if nodes else []}]
          interface = {'interface_id': interface_id, 'interfaces': interfaces,
              'zone_ref': zone_ref, 'comment': comment}
          
          tunnel_interface = TunnelInterface(**interface)
          self._engine.add_interface(tunnel_interface)
docs: Add a tunnel interface on a clustered engine. For tunnel interfaces
          on a cluster, you can specify a CVI only, NDI interfaces, or both.
          This interface type is only supported on layer 3 firewall engines.
          ::
  
              Add a tunnel CVI and NDI:
  
              engine.tunnel_interface.add_cluster_virtual_interface(
                  interface_id_id=3000,
                  cluster_virtual='4.4.4.1',
                  network_value='4.4.4.0/24',
                  nodes=nodes)
  
              Add tunnel NDI's only:
  
              engine.tunnel_interface.add_cluster_virtual_interface(
                  interface_id=3000,
                  nodes=nodes)
  
              Add tunnel CVI only:
  
              engine.tunnel_interface.add_cluster_virtual_interface(
                  interface_id=3000,
                  cluster_virtual='31.31.31.31',
                  network_value='31.31.31.0/24',
                  zone_ref='myzone')
  
          :param str,int interface_id: tunnel identifier (akin to interface_id)
          :param str cluster_virtual: CVI ipaddress (optional)
          :param str network_value: CVI network; required if ``cluster_virtual`` set
          :param list nodes: nodes for clustered engine with address,network_value,nodeid
          :param str zone_ref: zone reference, can be name, href or Zone
          :param str comment: optional comment