A method and system for automatically interconnecting IPv4 networks across an IPv6 network are disclosed. The method includes receiving an IPv4 packet at an ingress router in the IPv6 network and finding the longest match IPv4 routing entry for IPv4 addresses in the received packet to identify an egress router in the IPv6 network. The IPv4 packet is encapsulated to create an IPv6 packet, wherein destination and source addresses of the encapsulated packet identify a subnet router anycast corresponding to the ingress router and the egress router in the IPv6 network. The encapsulated packet is forwarded to the egress router.