Both the tunnel source and the tunnel destination are required to configure these type of tunnels.
Configured tunnels support encapsu- lated multicast packets.
The atun module is used to configure automatic tunnels. It supports IPv6 packets encapsulated within IPv4 packets. An IPv4 address is required for the tunnel source of these interfaces and the IPv4 compatible IPv6 source address must match this address. IPv6 packets using this interface must have IPv4 compatible source and destination addresses. If the des- tination of an automatic tunnel is a router, the packets will not be forwarded.