def _is_via_hub(node):
  """Check if a node is a Via Labs hub.
  The topology of this device is a 4-port hub,
  with another 4-port hub connected on port 4.
  """
  if '2109:2812' not in node.desc and '2109:0812' not in node.desc:
    return False
  if not node.HasPort(4):
    return False
  return ('2109:2812' in node.PortToDevice(4).desc
          or '2109:0812' in node.PortToDevice(4).desc)