docs: def str_to_ipmask(ipmask):
      '''
      Converts a string with the notation ip/mask (e.g. 192.168.1.1/24 or 192.168.1.1/255.255.255.0) to an hex mask
      '''
      v = ipmask.split("/")
      if len(v) > 2: raise Exception("bad mask format")
      mask_ip = ip2hex(v[0])
      if mask_ip is None: raise Exception("bad mask format")
      mask = v[1] if len(v) == 2 else 32
      try:
          mask = (0xffffffff00000000 >> int(mask)) & 0xffffffff
      except:
          mask = ip2hex(v[1])
      
      if mask is None: raise Exception("bad mask format")
      return mask_ip, mask