'Return netmask as an integer.
>>> "%X" % IP(\'195.185.0.0/16\').netmask().int()
\'FFFF0000\''

def netmask(self):

    bits = _ipVersionToLen(self._ipversion)
    locallen = (bits - self._prefixlen)
    return (((2 ** self._prefixlen) - 1) << locallen)
