def network(prefix, default_length=24):
    """
    Given a prefix, this function returns the corresponding network
    address.

    :type  prefix: string
    :param prefix: An IP prefix.
    :type  default_length: long
    :param default_length: The default ip prefix length.
    :rtype:  string
    :return: The IP network address.
    """
    address, pfxlen = parse_prefix(prefix, default_length)
    ip = ip2int(address)
    return int2ip(ip & pfxlen2mask_int(pfxlen))