If you have a Tunnel PIC installed in your router, you can configure IPv6-over-IPv4 tunnels. To do this, you configure a unicast tunnel across an existing IPv4 network infrastructure. IPv6 packets are encapsulated in IPv4 headers and sent across the IPv4 infrastructure through the configured tunnel. You manually configure configured tunnels on each end point.
IPv6-over-IPv4 tunnels are defined in RFC 2893, Transition Mechanisms for IPv6 Hosts and Routers. For information about configuring a unicast tunnel, see Configuring Unicast Tunnels. For an IPv6-over-IPv4 tunnel configuration example, see Example: Configuring an IPv6-over-IPv4 Tunnel.