US Patent 7305010 Multicast communication system

In order to make the client host capable of learning an accounting information or an authentication failure information, the accounting information or the authentication failure reason is notified from the routing device 2 to the client host 3, by adding an information regarding the accounting or an information regarding a reason for the authentication failure of the client host 3, to a packet of a protocol based on IGMP or MLD which is a multicast control packet between the client host 3 and the router device 2.