The automatic tunnels have a more limited use during early experimental deployment. Automatic tunnels require IPv4–compatible addresses and can be used to connect IPv6 nodes when IPv6 routers are not available. These tunnels can originate either on a dual host or on a dual router by configuring an automatic tunneling network interface. The tunnels always terminate on the dual host. These tunnels work by dynamically determining the destination IPv4 address (the endpoint of the tunnel) by extracting the address from the IPv4–compatible destination address.