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 can be considered a final IPv6 network architecture.
B . Overlay tunnels should only be considered as a transition technique toward a permanent solution.
C . Overlay tunnels can 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.

Answer: B

Explanation:

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/configuration/xe-3s/ir-xe-3s-book/ip6-ip4-gre-tunls-xe.pdf

"The use of overlay tunnels should be considered as a transition technique toward a network that supports both the IPv4 and IPv6 protocol stacks or just the IPv6 protocol stack."