Which design consideration must be made when using IPv6 overlay tunnels?

Which design consideration must be made when using IPv6 overlay tunnels?

A. Overlay tunnels that connect isolated IPv6 networks are considered a final IPv6 network architecture. B. Overlay tunnels should only be considered as a transition technique toward a permanent solution. C. Overlay tunnels should be configured only between border devices and require only the IPv6 protocol stack. D. Overlay tunneling encapsulates IPv4 packets in IPv6 packets for delivery across an IPv6 infrastructure.