code: def interface(enode, portlbl, addr=None, up=None, shell=None):
      
      assert portlbl
      port = enode.ports[portlbl]
  
      if addr is not None:
          assert ip_interface(addr)
          cmd = 'ip addr add {addr} dev {port}'.format(addr=addr, port=port)
          response = enode(cmd, shell=shell)
          assert not response
  
      if up is not None:
          cmd = 'ip link set dev {port} {state}'.format(
              port=port, state='up' if up else 'down'
          )
          response = enode(cmd, shell=shell)
          assert not response
docs: Configure a interface.
  
      All parameters left as ``None`` are ignored and thus no configuration
      action is taken for that parameter (left "as-is").
  
      :param enode: Engine node to communicate with.
      :type enode: topology.platforms.base.BaseNode
      :param str portlbl: Port label to configure. Port label will be mapped to
       real port automatically.
      :param str addr: IPv4 or IPv6 address to add to the interface:
       - IPv4 address and netmask to assign to the interface in the form
       ``'192.168.20.20/24'``.
       - IPv6 address and subnets to assign to the interface in the form
       ``'2001::1/120'``.
      :param bool up: Bring up or down the interface.
      :param str shell: Shell name to execute commands.
       If ``None``, use the Engine Node default shell.