Patent ID: 7660324

Claim:
A virtual private network (VPN) construction system for a public data communication network comprising: first relaying apparatuses, with one or more virtual routers each of which is associated with a VPN-ID and a multicast address in a table, generating and multicasting control packets each of which contains a source address of each virtual router and is transmitted for the multicast address as a destination address corresponding to the VPN-ID of each virtual router, and second relaying apparatuses, with one or more virtual routers each of which is associated with a VPN-ID and a multicast address in a table, accepting only the control packets of the multicast address corresponding to the VPN-ID of each virtual router of the second relaying apparatuses, establishing virtual links using the source address in the control packets with the first relaying apparatuses and returning reply packets to the first relaying apparatuses through the virtual links, whereby the virtual private network is constructed between the virtual routers that are specific to a same multicast address in the first and the second relaying apparatuses, with the virtual links established between all pairs of the virtual routers and with virtual interfaces receiving packets from outside the public data communication network.