@abc.abstractmethod<EOL><INDENT>def enable_internal_network_NAT(self, router_info, port, ext_gw_port):<DEDENT>
pass<EOL>
Enable NAT on an internal network.

        :param router_info: RouterInfo object for this router
        :param port: port dictionary for the port where the internal
            network is connected
        :param ext_gw_port: port dictionary for the port where the external
            gateway network is connected
        :returns: None