@classmethod
def create_conntrack_helper(cls, router_id, helper, protocol, port, client=None
    ):
    """Create a conntrack helper

        Create a conntrack helper and schedule it for later deletion. If a
        client is passed, then it is used for deleteing the CTH too.

        :param router_id: The ID of the Neutron router associated to the
        conntrack helper.

        :param helper: The conntrack helper module alias

        :param protocol: The conntrack helper IP protocol used in the conntrack
        helper.

        :param port: The conntrack helper IP protocol port number for the
        conntrack helper.

        :param client: network client to be used for creating and cleaning up
        the conntrack helper.
        """
    client = client or cls.client
    cth = client.create_conntrack_helper(router_id, helper, protocol, port)[
        'conntrack_helper']
    cth['router_id'] = router_id
    cth['client'] = client
    cls.conntrack_helpers.append(cth)
    return cth
