code: def netmask(mask):
      '''
      Returns True if the value passed is a valid netmask, otherwise return False
      '''
      if not isinstance(mask, string_types):
          return False
  
      octets = mask.split('.')
      if not len(octets) == 4:
          return False
  
      return ipv4_addr(mask) and octets == sorted(octets, reverse=Truef netmask(mask):
      '''
      Returns True if the value passed is a valid netmask, otherwise return False
      '''
      if not isinstance(mask, string_types):
          return False
  
      octets = mask.split('.')
      if not len(octets) == 4:
          return False
  
      return ipv4_addr(mask) and octets == sorted(octets, reverse=True)
docs: Returns True if the value passed is a valid netmask, otherwise return False