The present invention relates to a multicast communication method. The invention also relates to a multicast communication method which is applied to, for example, a method of making an IPv4 network-compatible multicast application operative on an IPv6 network, a packet generation method, an IP-network-dedicated translator, an NAT (Network Address Translator), a memory medium having a packet generation program recorded thereon, and the like.
In the field of information communication, generally, there is a method called multicast distribution as a method of simultaneously distributing same data from one host to a plurality of hosts. In the multicast distribution, one group is formed by a plurality of hosts and the same data is distributed from one of the hosts in the group to all of the other hosts by using one multicast packet.
The standard protocol in the Internet is a TCP/IP (Transmission Control Protocol/Internet Protocol) and the IP of version 4 (hereinafter, referred to as an IPv4) is widespread at the present time. Although the IP is at present being rapidly widespread for various communication services in cooperation with the spread of the Internet or the like, there is a serious problem such as a lack of IP addresses. As means for solving such a problem, the IP of version 6 (hereinafter, referred to as an IPv6) has been proposed at present. Also in the TCP/IPv4 and TCP/IPv6, there is a technique called an IP multicast using multicast distribution.
In the IP multicast, a specific IP address called an IP multicast address is specified every group and data is distributed to each host by using an IP multicast packet in which the IP multicast address is used as a destination IP address. As one of the protocols for the IPv4 multicast, for example, there is the IGMP (Internet Group Management Protocol) disclosed in RFC (Request For Comment) 1112 and RFC2236 as documents issued from the IETF (Internet Engineering Task Force). The IGMP is a protocol for allowing an IPv4 host to request an adjacent router to perform multicast distribution. Thus, the IPv4 host can receive the IPv4 multicast packet.
As one of protocols for the IPv6 multicast, there is the MLD (Multicast Listener Discovery) disclosed in RFC2710. The MLD is a protocol for allowing an IPv6 host to request an adjacent router to perform multicast distribution in a manner similar to the IGMP. Thus, the host can receive an IPv6 multicast packet.
At present, a large scale LAN is being formed in a form such that an LAN according to the IPv6 and an LAN according to the IPv4 mixedly exist. There is an RFC1933 as a document of standardization regarding the mutual adjacency of the LAN according to the IPv6 and the LAN according to the IPv4. According to the RFC1933 (Transition Mechanism for IPv6 Hosts and Routers: R. Gilligam, 1996. 4, IETF), in a communication control apparatus having IPv6 software, mutual adjacency of an IPv6 network is enabled by mapping an IPv4 address to an IPv6 address. A technique in which an IPv4-to-IPv6 protocol translation control module in the communication control apparatus enables an IPv4 application and an IPv6 host to communicate in unicast communication has been disclosed in JP-A-11-252172 (Japanese Patent Application No. 10-46739).